US20170048939A1 - Backlight module with mjt led and backlight unit incluing the same - Google Patents

Abstract

A backlight unit including a backlight module and a backlight control module. The backlight module includes a printed circuit board including blocks, and light emitting diode (LED) chips disposed on the blocks, and the backlight control module is configured to perform a dimming control of the LED chips. Each of the LED chips includes light emitting cells spaced apart from each other, each of the light emitting cells including a lower semiconductor layer, an upper semiconductor layer, and an active layer therebewteen, in which the lower semiconductor layers are partially exposed, connection structures electrically connecting the light emitting cells to each other, and an insulation layer disposed between the light emitting cells and the connection structures, the insulation layer covering a portion of the exposed lower semiconductor layers and having a width wider than the connection structures.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 14/812,437, filed on Jul. 29, 2015, which is a continuation-in-part of U.S. patent application Ser. No. 14/339,051, filed on Jul. 23, 2014, and claims priority from and the benefit of Korean Patent Application No. 10-2014-0026574, filed on Mar. 6, 2014, and Korean Patent Application No. 10-2015-0095536, filed on Jul. 3, 2015, all of which are hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND
• Field
• The present disclosure relates to a backlight module using a multi junction technology (MJT) light emitting diode (LED) and a backlight unit including the same. More particularly, the present disclosure relates to a backlight module which employs an MJT LED configured to increase an effective light emitting area of each of light emitting cells to allow operation at low current, and a backlight unit including the same.
• Description of the Background
• A liquid crystal display creates an image by controlling transmittance of a backlight light source. Although a cold cathode fluorescent lamp (CCFL) has generally been used as a backlight light source in the related art, light emitting diodes (hereinafter, LEDs) are being recently used due to various advantages such as low power consumption, long lifespan, eco-friendliness, and the like.
• Backlight units can be classified into edge type backlight units and direct type backlight units according to the locations of LEDs for backlighting a liquid crystal display. In an edge type backlight unit, with LEDs arranged as light sources on a side surface of a light guide plate, light entering the light guide plate from the light sources is used for backlighting of a liquid crystal panel. Thus, the edge type backlight unit can reduce the number of LEDs and does not require strict control of quality deviation among the LEDs, thereby enabling manufacture of low power consumption products, which is advantageous in terms of cost. However, in the edge type backlight unit it is difficult to overcome contrast between a corner area and a central area of the liquid crystal display and it is difficult to create high quality images.
• Alternatively, a direct type backlight unit is placed under a liquid crystal panel and allows light emitted from a surface light source, which has substantially the same area as that of the liquid crystal panel, to directly illuminate a front side of the liquid crystal panel. The direct type backlight unit can overcome contrast difference between a corner area and a central area of the liquid crystal display and can achieve high quality images.
• However, in the direct type backlight unit, if each of the LEDs does not illuminate a relatively wide area for backlighting, a number of LEDs must be densely arranged, thereby causing increase in power consumption. Moreover, deviation in quality between the LEDs can make it difficult to secure a uniform screen illumination due to uneven backlighting of a liquid crystal panel.
• Particularly, with the increasing size of liquid crystal panels, the size of the direct type backlight unit is also increased, thereby causing deterioration in stability or reliability of the direct type backlight unit. Specifically, since the LED backlight unit controls the operating current supplied to a plurality of LED groups, that is, LED arrays, through a plurality of LED drive circuits, the number of LED drive circuits and the number of LED corresponding arrays are significantly increased as the size of the LED backlight unit increases. As a result, a disconnection can occur between the plurality of LEDs or LED arrays arranged adjacent each other, whereby the drive circuits are damaged due to overcurrent, overvoltage, or overheating, thereby deteriorating the stability and reliability of the backlight unit.
• FIG. 1 is a configuration block diagram of a typical backlight unit using LEDs in the related art. With reference toFIG. 1, problems of the related art will be described in more detail. As shown inFIG. 1, atypical backlight unit1 includes abacklight control module2 and abacklight module5.
• Thebacklight control module2 includes anoperating power generator3, which generates/outputs DC power based on input voltage Vin input from an external power source, and anoperation controller4 controlling operation of each of a plurality of LED arrays6a-6nconstituting thebacklight module5. Theoperating power generator3 generally generates DC voltages such as 12V, 24V, 48V, and the like as operating power.
• Thebacklight module5 includes a plurality of LED arrays6a-6neach formed by connecting a plurality of LEDs in series, and an optical unit (not shown) for enhancing efficacy of light emitted from the plurality of LED arrays6a-6n. InFIG. 1, thebacklight unit5 includes n LED arrays6a-6nconnected to each other in parallel and each including five LEDs connected to each other in series. Here, since each of the LEDs used in the backlight unit generally has a forward voltage level in the range from 3V to 6.5V and is difficult to individually control/operate when connected to theoperating power generator3, plural LEDs are connected to each other in series to constitute LED arrays such that each of the LED arrays can be operated/controlled. In such atypical backlight unit1 in the related art, theoperation controller4 is configured to control brightness of all of the LED arrays6a-6nconstituting thebacklight module5 through pulse width modulation (PWM) control with respect to the operating power supplied to thebacklight module5 in response to an external dimming signal (Dim). Otherwise, in such atypical backlight unit1, theoperation controller4 adjusts the operating current flowing through a specific LED array among the n LED arrays6a-6nin response to an external dimming signal (Dim) to control brightness of the specific LED array.
• LEDs used in such atypical backlight unit1 are generally single-cell LEDs capable of being operated at low voltage and high current. For example, such a single-cell LED has an operating voltage of 3.6V and can be operated at an operating current of 250-500 mA. Thus, in order to control operation of thebacklight module5 constituted by such single-cell LEDs, peripheral circuits including theoperation controller4 in the related art must be constituted by large capacity electronic devices capable of handling large current, thereby causing increase in manufacturing costs of thebacklight unit1. In addition, the peripheral circuits including theoperation controller4 are damaged due to the high current operation characteristics of the aforementioned typical single-cell LEDs, thereby causing deterioration in stability or reliability of thebacklight unit1. In addition, the high current operation characteristics of the single-cell LEDs cause an increase in power consumption and a droop phenomenon.
SUMMARY
• The present disclosure is aimed at providing a backlight module which can be operated at low current using an MJT LED including a plurality of light emitting cells and a backlight unit including the same.
• In addition, the present disclosure is aimed at providing an MJT LED chip, which can increase an effective light emitting area of a light emitting cell, and a method of manufacturing the same.
• Further, the present invention is aimed at providing a backlight unit, which allows a backlight module to be operated at low current using the aforementioned MJT LED, thereby improving stability and reliability of drive circuits for controlling operation of the backlight module, and enabling reduction in manufacturing costs.
• Further, the present disclosure is aimed at providing a backlight unit, which allows a backlight module to be operated at low current using the aforementioned MJT LED, thereby improving power efficiency and luminous efficacy while preventing a droop phenomenon due to operation at high current.
• Further, the present disclosure is aimed at providing a backlight unit, in which a backlight module is constituted by MJT LEDs, thereby minimizing the number of LEDs while enabling individual control of the MJT LEDs.
• The above and other objects and advantageous effects of the present disclosure can be obtained by the following features of the present disclosure.
• In accordance with one aspect of the present disclosure, a backlight module includes a printed circuit board; a plurality of MJT LEDs disposed on the printed circuit board; and a plurality of optical members disposed on the MJT LEDs or the printed circuit board so as to correspond to the MJT LEDs and each including a light incident face through which light emitted from the corresponding MJT LED enters the optical member and a light exit face through which light exits the optical member at a wider beam angle than that of the corresponding MJT LED, wherein each of the MJT LEDs includes a first light emitting cell and a second light emitting cell separated from each other on a growth substrate; a first transparent electrode layer placed on the first light emitting cell and electrically connected to the first light emitting cell; a current blocking layer placed between the first light emitting cell and the first transparent electrode layer and separating a portion of the first transparent electrode layer from the first light emitting cell; an interconnection line electrically connecting the first light emitting cell to the second light emitting cell; and an insulation layer separating the interconnection line from a side surface of the first light emitting cell. Here, the second light emitting cell has a slanted side surface; and the interconnection line includes a first connection section for electrical connection to the first light emitting cell and a second connection section for electrical connection to the second light emitting cell. The first connection section contacts the first transparent electrode layer within an upper area of the current blocking layer, and the second connection section contacts the slanted side surface of the second light emitting cell.
• In one aspect, each of the MJT LEDs includes first to N-th light emitting cells (N being a natural number of 2 or more), and the N-th light emitting cell may be electrically connected to a (N-1)th light emitting cell using the same structure as a connection structure between the first light emitting cell and a second light emitting cell.
• In one aspect, the first to N-th light emitting cells are connected to each other in series and each operated by an operating voltage of 2.5V to 4 V. Here, each of the MJT LEDs may be operated at an operating voltage of at least 10 V or more.
• In one aspect, each of the MJT LEDs includes three light emitting cells each being operated at an operating voltage of 3V to 3.6V, and is operated at an operating voltage of 12V to 14V.
• In one aspect, the light exit face includes a concave section formed near a central axis of the optical member and a convex section extending from the concave section and separated from the central axis of the optical member.
• In one aspect, the light exit face includes a total reflection surface so as to form an apex under the central axis of the optical member.
• In one aspect, the light incident face includes an opening formed near the central axis of the optical member, and the height of the opening is 1.5 times or more a width thereof.
• In one aspect, each of the optical members has a light scattering pattern formed on at least a portion of a bottom surface facing the printed circuit board.
• In one aspect, each of the optical members includes a lower surface having a concave section, through which light emitted from the MJT LED enters the optical member; and an upper surface through which light entering the optical member through the concave section exits the optical member. Here, the upper surface includes a concave surface placed at the central axis of the optical member, and the concave section of the lower surface includes at least one of a perpendicular surface relative to the central axis and a downwardly convex surface, and the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface may be placed within a narrower area than an area for an entrance of the concave section.
• In one aspect, the upper surface and the concave section of the optical member form a mirror symmetry structure relative to a plane passing through the central axis of the optical member.
• In one aspect, the upper surface and the concave section of the optical member form a rotational body shape relative to the central axis of the optical member.
• In one aspect, each of the optical members has a light scattering pattern formed on the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface within the concave section of the lower surface and on a surface closer to the central axis than the at least one surface.
• In one aspect, each of the optical members has a light scattering pattern formed on the concave surface of the upper surface.
• In one aspect, each of the optical members further includes a material layer having a different index of refraction than the optical member on the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface within the concave section of the lower surface and on a surface closer to the central axis than the at least one surface.
• In one aspect, each of the optical members further includes a material layer having a different index of refraction than the optical member on the concave surface of the upper surface.
• In one aspect, the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface is defined within a narrower area than an area surrounded by an inflection curve at which the concave surface of the upper surface meets the convex surface thereof.
• In one aspect, the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface is defined within a narrower area than an area of a light exit face of the light emitting diode.
• In one aspect, each of the optical members further includes a flange connecting the upper surface and the lower surface and the at least one of the perpendicular surface relative to the central axis and the downwardly convex surface within the concave section is placed above the flange.
• In one aspect, each of the optical members has an optical axis L, a light incident section, and a light exit face, and is formed of a material, the index of refraction of which is higher than that of a material adjoining the light incident section and that of a material adjoining the light exit face.
• In one aspect, the light incident section is formed such that the shortest distance from a point (p) on the optical axis L to an apex of the light incident section is greater than the shortest distance (a) from the point (p) to a side surface of the light incident section within an angle of 50° or less from the optical axis L.
• In one aspect, an upper center of the light exit face is formed of a flat surface or a convex curve.
• In one aspect, the light incident section includes a lower entrance placed adjacent the light emitting diode and having a circular shape, and has a shape gradually converging to the apex while maintaining a circular shape.
• In one aspect, the light incident section has a height which is 1.5 times greater than a radius of the lower entrance.
• In one aspect, the material adjoining the light incident section is air.
• In one aspect, the material adjoining the light exit face is air.
• In one aspect, the optical members are formed of a resin or glass.
• In accordance with another aspect of the present disclosure, a backlight unit includes the aforementioned backlight module; and a backlight control module supplying DC operating voltage to the plurality of MJT LEDs within the backlight module and independently controlling operation of each of the plurality of MJT LEDs.
• In one aspect, the backlight control module supplies the DC operating voltage to each of the plurality of MJT LEDs within the backlight module, and performs pulse width modulation control with respect to the DC operating voltage supplied to at least one MJT LED among the plurality of MJT LEDs in response to a dimming signal to perform dimming control of the at least one MJT LED.
• In one aspect, the backlight control module allows independent detection and control of operating current of each of the plurality of MJT LEDs within the backlight module, and controls operating current of at least one MJT LED among the plurality of MJT LEDs in response to a dimming signal to perform dimming control of the at least one MJT LED.
• According to an exemplary embodiment of the present disclosure, there is provided a backlight unit including: a printed circuit board including blocks; a backlight module including multi junction technology (MJT) light emitting diodes(LEDs) respectively disposed on the blocks; and a backlight control module configured to provide an operating voltage to the MJT LEDs within the backlight module, wherein each of the blocks includes at least one of the MJT LEDs, and the backlight control module is configured to independently control an operation of each of the MJT LEDs.
• The backlight control module may include an operating power generator; and an operation controller.
• The operating power generator may be configured to independently provide the operating voltage to each of the MJT LEDs within the backlight module, and the operation controller may be configured to perform a dimming control of at least one of the MJT LEDs by performing a pulse width modulation (PWM) control in response to a dimming signal of the backlight control module.
• The operation controller may be configured to generate a dimming control signal of which a pulse width is modulated or a duty ratio is modulated.
• The operation controller may be configured to independently detect and control an operating current of at least one of the MJT LEDs within the backlight module.
• The operation controller may be configured to perform a dimming control of at least one of the MJT LEDs by controlling the operating current of at least one of the MJT LEDs in response to a dimming signal of the backlight control module.
• An anode terminal of at least one of the MJT LEDs may be connected to the operating power generator, and a cathode terminal of at least one of the MJT LEDs may be connected to the operation controller.
• The backlight unit may further include an optical member disposed on the MJT LEDs or the printed circuit board so as to correspond to the MJT LEDs.
• The optical member may include a light incident face through which light emitted from the MJT LED enters and a light exit face through which the light exits at a wider light directivity angle than a light directivity angle of the MJT LEDs.
• of the backlight unit may include optical members, and each of the optical members may be respectively disposed on one of the MJT LEDs.
• The optical member may include a molded-resin on the MJT LEDs.
• Each of the blocks may include one optical member.
• Each of the blocks may have a horizontal length of 60 mm or less.
• Each of the blocks may have a vertical length of 55 mm or less.
• The blocks may include M×N blocks, and the blocks may constitute an M×N matrix arrangement.
• At least one block of the blocks may include at least one of the MJT LEDs.
• The MJT LEDs may be configured to include first to N-th light emitting cells (N is a natural number of 2 or greater), and the N-th light emitting cell may be electrically connected to an N-1-th light emitting cell in the same structure as the first light emitting cell and a second light emitting cell are electrically connected to each other.
• The first to N-th light emitting cells may be connected to each other in series and are configured to be operated by an operating voltage of 2.5V to 4V, and the MJT LEDs may be configured to be operated by the operating voltage of at least 10V or greater.
• The plurality of MJT LEDs may include: a first light emitting cell and a second light emitting cell disposed on a growth substrate to be spaced apart from each other, each of the first light emitting cell and the second light emitting cell including a lower semiconductor layer, an upper semiconductor layer disposed on the lower semiconductor layer, and an active layer disposed between the lower semiconductor layer and the upper semiconductor layer; a first transparent electrode layer disposed on the first light emitting cell and electrically connected to the first light emitting cell; an interconnection line electrically connecting the first light emitting cell and the second light emitting cell to each other; and an insulation layer spacing apart the interconnection line from a side surface of the first light emitting cell. The interconnection line has a first connection section for an electrical connection to the first light emitting cell, and a second connection section for an electrical connection to the second light emitting cell, one surface of the lower semiconductor layer may include an exposed region exposing the lower semiconductor layer, the first connection section may contact the first transparent electrode layer, and the second connection section may be electrically connected to the lower semiconductor layer of the second light emitting cell through the exposed region.
• A portion of the first transparent electrode layer may be connected to the second light emitting cell.
• The portion of the first transparent electrode layer may be disposed on the first light emitting cell, between the first light emitting cell and the second light emitting cell, and on a side surface of the lower semiconductor layer of the second light emitting cell.
• A width of a portion of the first transparent electrode layer disposed on the side surface of the lower semiconductor layer of the second light emitting cell may be wider than a width of a portion of the interconnection line disposed on the side surface of the lower semiconductor layer of the second light emitting cell.
• A width of a portion of the first transparent electrode layer disposed between the first light emitting cell and the second light emitting cell may be wider than a width of a portion of the interconnection line disposed between the first light emitting cell and the second light emitting cell.
• The first transparent electrode layer may space apart the interconnection line from the insulation layer.
• A portion of the insulation layer may be disposed on a portion of the growth substrate disposed between the first light emitting cell and the second light emitting cell.
• The backlight unit may further include a current blocking layer disposed between the first light emitting cell and the first transparent electrode layer to space apart a portion of the first transparent electrode layer from the first light emitting cell.
• The first transparent electrode layer may be disposed between the second connection section and the lower semiconductor layer of the second light emitting cell.
• The backlight unit may further include a floodlighting plate disposed on the printed circuit board, wherein a distance between an upper surface of the printed circuit board and a lower surface of the floodlighting plate is 18 mm or more.
• The operation controller may include a switch controller that electrically connects or insulates the MJT LEDs to and from each other.
• The switch controller may connect the MJT LEDs in series and/or in parallel to each other.
• The backlight module may include a phosphor and further includes a wavelength conversion layer covering the MJT LEDs, and light emitted from the MJT LEDs to penetrate through the wavelength conversion layer may have a National Television System Committee (NTSC) color reproduction ratio of 70% or greater.
• As the number of light emitting cells within an MJT LED increases, an area of a block associated with the MJT LED may decrease.
• According to another exemplary embodiment of the present disclosure, there is provided a backlight unit including: a printed circuit board including blocks; and a backlight module including multi junction technology (MJT) light emitting diodes (LEDs) disposed on the plurality of blocks; wherein the MJT LEDs include: a first light emitting cell and a second light emitting cell disposed on a growth substrate to be spaced apart from each other and each including a lower semiconductor layer, an upper semiconductor layer disposed on the lower semiconductor layer, and an active layer disposed between the lower semiconductor layer and the upper semiconductor layer; a first transparent electrode layer disposed on the first light emitting cell and electrically connected to the first light emitting cell; an interconnection line electrically connecting the first light emitting cell and the second light emitting cell to each other; and an insulation layer spacing apart the interconnection line from a side surface of the first light emitting cell. The interconnection line has a first connection section for an electrical connection to the first light emitting cell, and a second connection section for an electrical connection to the second light emitting cell, one surface of the lower semiconductor layer includes an exposed region exposing the lower semiconductor layer, the first connection section contacts the first transparent electrode layer, the second connection section is electrically connected to the lower semiconductor layer of the second light emitting cell through the exposed region, and an operation of each of the MJT LEDs is configured to be independently controlled.
• A portion of the first transparent electrode layer may be connected to the second light emitting cell.
• The portion of the first transparent electrode layer may be disposed on the first light emitting cell, between the first light emitting cell and the second light emitting cell, and on a side surface of the lower semiconductor layer of the second light emitting cell.
• A width of a portion of the first transparent electrode layer disposed on the side surface of the lower semiconductor layer of the second light emitting cell may be wider than a width of a portion of the interconnection line disposed on the side surface of the lower semiconductor layer of the second light emitting cell.
• A width of a portion of the first transparent electrode layer disposed between the first light emitting cell and the second light emitting cell may be wider than a width of a portion of the interconnection line disposed between the first light emitting cell and the second light emitting cell.
• The first transparent electrode layer may space apart the interconnection line from the insulation layer.
• A portion of the insulation layer may be disposed on a portion of the growth substrate disposed between the first light emitting cell and the second light emitting cell.
• The backlight unit may further include a current blocking layer disposed between the first light emitting cell and the first transparent electrode layer to space apart a portion of the first transparent electrode layer from the first light emitting cell.
• The first transparent electrode layer may be disposed between the second connection section and the lower semiconductor layer of the second light emitting cell.
• According to embodiments of the present disclosure, the backlight module is fabricated using MJT LEDs having low current operation characteristics, thereby enabling low current operation of the backlight module and the backlight unit including the same.
• In addition, according to the embodiments of the present disclosure, one connection section of the interconnection line electrically contacts a slanted side surface of light emitting cell, thereby increasing an effective light emitting area of each of light emitting cells in an MJT LED chip.
• Further, according to the embodiments of the present disclosure, it is possible to enhance stability and reliability of drive circuits for controlling operation of the backlight module while reducing manufacturing costs.
• Further, according to the embodiments of the present disclosure, the backlight unit has improved power efficiency and luminous efficacy, and can prevent a droop phenomenon due to operation at high current.
• Further, according to the embodiments of the present disclosure, it is possible to minimize the number of LEDs constituting the backlight module and to allow individual operation of the MJT LEDs constituting the backlight module.
BRIEF DESCRIPTION OF THE DRAWINGS
• The above and other aspects, features, and advantages of the present disclosure will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings, in which:
• FIG. 1 is a configuration block diagram of a typical backlight unit including LEDs in the related art;
• FIG. 2 is a schematic block diagram of a backlight unit employing MJT LEDs according to one exemplary embodiment of the present disclosure;
• FIG. 3 is a schematic sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure;
• FIG. 4 is a schematic perspective view of the MJT LED according to the one exemplary embodiment of the present disclosure;
• FIG. 5 is a schematic plan view of an MJT LED chip according to one exemplary embodiment of the present disclosure;
• FIG. 6 is a schematic sectional view of the MJT LED chip taken along line B-B ofFIG. 5;
• FIG. 7 toFIG. 13 are schematic sectional views illustrating a method of fabricating an MJT LED chip according to one exemplary embodiment of the present disclosure;
• FIG. 14 is a schematic sectional view of an MJT LED chip according to another exemplary embodiment of the present disclosure;
• FIG. 15 toFIG. 18 are schematic sectional views illustrating a method of fabricating an MJT LED chip according to another exemplary embodiment of the present disclosure;
• FIG. 19A,FIG. 19B,FIG. 19C andFIG. 19D show sectional views of various modifications of an optical member according to the present disclosure;
• FIG. 20A andFIG. 20B show sectional views of an optical member, illustrating an MJT LED module according to a further exemplary embodiment of the present disclosure;
• FIG. 21 is a sectional view illustrating dimensions of an MJT LED module used for simulation;
• FIG. 22A,FIG. 22B andFIG. 22C show graphs depicting a shape of an optical member ofFIG. 21;
• FIG. 23 shows traveling directions of light beams entering the optical member ofFIG. 21;
• FIG. 24A andFIG. 24B show graphs depicting illuminance distribution. Specifically,FIG. 24A is a graph depicting illuminance distribution of an MJT LED, andFIG. 24B is a graph showing illuminance distribution of an MJT LED module using an optical member;
• FIG. 25A andFIG. 25B show graphs depicting light beam distributions. Specifically,FIG. 25A is a graph depicting a light beam distribution of an MJT LED andFIG. 25B is a graph depicting a light beam distribution of an MJT LED module using an optical member;
• FIG. 26 is a sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure;
• FIG. 27A,FIG. 27B andFIG. 27C illustrate sectional views of the MJT LED module taken along lines a-a, b-b and c-c ofFIG. 26, respectively;
• FIG. 28 is a detailed view of an optical member of the MJT LED module shown inFIG. 26;
• FIG. 29 shows a light beam angle distribution of the MJT LED module using the optical member ofFIG. 28;
• FIG. 30 is a sectional view of an optical member according to another exemplary embodiment of the present disclosure;
• FIG. 31 shows a beam angle distribution curve of an MJT LED module using the optical member ofFIG. 30;
• FIG. 32A andFIG. 32B show an optical member according to Comparative Example 1 and a beam angle distribution curve thereof;
• FIG. 33A andFIG. 33B show an optical member according to Comparative Example 2 and a light beam angle distribution thereof;
• FIG. 34 is a schematic plan view of an MJT LED chip according to one exemplary embodiment of the present disclosure;
• FIG. 35 is a schematic cross-sectional view of the MJT LED chip taken along section B-B ofFIG. 34;
• FIG. 36 throughFIG. 41 are schematic cross-sectional views illustrating a method of fabricating an MJT LED chip according to one exemplary embodiment of the present disclosure;
• FIG. 42 is a schematic cross-sectional view of an MJT LED chip according to another exemplary embodiment of the present disclosure;
• FIG. 43A andFIG. 43B are schematic views comparing a backlight unit (FIG. 43A) in the related art with a backlight unit (FIG. 43B) according to one exemplary embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
• The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are illustrated. These embodiments will be described such that the disclosure can be easily understood by a person having ordinary knowledge in the art. Here, although various embodiments are disclosed herein, it should be understood that these embodiments are not intended to be exclusive. For example, individual structures, elements or features of a particular embodiment are not limited to that particular embodiment and can be applied to other embodiments without departing from the spirit and scope of the disclosure. In addition, it should be understood that locations or arrangement of individual components in each of the embodiments may be changed without departing from the spirit and scope of the present disclosure. Therefore, the following embodiments are not to be construed as limiting the disclosure, and the present disclosure should be limited only by the claims and equivalents thereof. Like components will be denoted by like reference numerals, and lengths, areas, thicknesses and shapes of the components are not drawn to scale throughout the accompanying drawings.
• Now, exemplary embodiments of the disclosure will be described in detail with reference to the accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art.
Exemplary Embodiment of the Present Disclosure
• As used herein, the term “MJT LED chip” means a single LED chip, in which a plurality of light emitting cells is connected to each other via interconnection lines. The MJT LED chip may include N light emitting cells (N is an integer of 2 or more), in which N may be set in various ways as needed. Further, each of the light emitting cells may have a forward voltage in the range from 3V to 3.6V, but is not limited thereto. Accordingly, a forward voltage of a certain MJT LED chip (or MJT LED) is proportional to the number of light emitting cells included in the corresponding MJT LED chip. Since the number of light emitting cells included in the MJT LED chip may be set in various ways as needed, the MJT LED chip according to the present disclosure may be configured to have an operating voltage of 6V to 36V depending upon a specification of an operating power generator (for example, a DC converter) used in a backlight unit, but is not limited thereto. Further, operating current of the MJT LED chip is much smaller than a typical single-cell LED, and may range, for example, from 20 mA to 40 mA, without being limited thereto.
• In addition, the term “MJT LED” refers to a light emitting device or an LED package, on which the MJT LED chip according to the present disclosure is mounted.
• Further, the term “MJT LED module” refers to a component in which a single MJT LED and a single optical member corresponding to the MJT LED are coupled to each other. The corresponding optical member may be directly placed on the MJT LED, or may be placed on a printed circuit board on which the MJT LED is mounted. Regardless of displacement of the optical member, the case wherein a single MJT LED and a single optical member corresponding thereto are coupled to each other will be referred to as the MJT LED module.
• Further, the term “backlight module” means a lighting module, in which a plurality of MJT LEDs is disposed on a printed circuit board and optical members are provided corresponding to the respective MJT LEDs. Thus, the term “backlight module” may mean a lighting module in which plural MJT LED modules are mounted on a printed circuit board in a predetermined manner. In one aspect, a backlight module according to one exemplary embodiment of the disclosure may be a direct type backlight module. However, it should be understood that the present disclosure is not limited thereto. In other embodiments, the backlight module according to the present disclosure may be used as a light source for surface lighting. Accordingly, it will be apparent to those skilled in the art that any component including the subject matter of the backlight module according to the present disclosure falls within the scope of the present disclosure, despite the name of the component.
• Overview of Backlight Unit Using MJT LEDs
• Before detailed descriptions of the backlight unit according to the present disclosure are given, several technical features of the present disclosure will be described. The present disclosure is based on characteristics of an MJT LED in order to solve the aforementioned problems in the related art. That is, in order to solve the problems due to low voltage and high current operation characteristics of a typical single-cell LED in the related art, the present disclosure has been created based on high voltage and low current operation characteristics of the MJT LED (for example, an operating voltage of 6 V to 36 V and an operating current of 20 mA to 40 mA), and provides a backlight module using such an MJT LED. As described above, unlike a typical single-cell LED, the MJT LED may include any number of light emitting cells and may have various forward voltages depending upon the number of light emitting cells included therein. In addition, since the MJT LED includes a plurality of light emitting cells, it is possible to illuminate a wider area than the typical single-cell LED, and since the MJT LED is constituted by a single MJT LED chip, design and application of an optical member therefor can be easily achieved. Thus, when using such an MJT LED, one divided area among a plurality of divided areas in a liquid crystal panel can be covered by one MJT LED module (that is, one MJT LED and one optical member). As a result, the number of LEDs required for the backlight module is reduced as compared with the typical single-cell LED. Consequently, according to the present disclosure, a plurality of MJT LED modules is used to constitute a backlight module and a backlight unit is configured to allow independent control of each of the MJT LEDs constituting the backlight module, thereby achieving the above and other objects of the present disclosure.
• Now, referring toFIG. 2 throughFIG. 4 andFIG. 43, abacklight unit1000 according to one exemplary embodiment of the disclosure will be described in more detail.
• First,FIG. 2 is a schematic block diagram of a backlight unit employing MJT LEDs according to one exemplary embodiment of the present disclosure. Referring toFIG. 2, thebacklight unit1000 according to this embodiment includes abacklight control module400 and abacklight module300. Further, the backlight units illustrated in the present disclosure may further include a floodlighting plate (not shown).
• More specifically, thebacklight control module400 according to this disclosure includes an operating power generator410, which generates/outputs DC power based on input voltage Vin input from an external power source, and anoperation controller420 controlling operation of each of a plurality ofMJT LEDs100 constituting the backlight module300 (on/off control and dimming control). The operating power generator410 generally generates stable DC voltage such as 12V, 24V, 48V, and the like, as operating power and supplies the DC voltage to the plurality ofMJT LEDs100 constituting thebacklight module300. Here, the input voltage Vin supplied to the operating power generator410 may be a commercially available alternating voltage of 220V or 110V. The operating power generator410 may have substantially the same configuration as the typical operating power generator410 as shown inFIG. 1.
• Thebacklight module300 according to this disclosure may include a plurality ofMJT LEDs100 and optical members (not shown inFIG. 2) corresponding to therespective MJT LEDs100 and disposed in a regular arrangement (for example, in a matrix arrangement) on a printed circuit board (not shown inFIG. 2).
• FIG. 43B is a schematic view illustrating a configuration of the backlight unit according to the present disclosure. Referring toFIG. 43B, the printedcircuit board110 may include a plurality ofblocks110b. Theblock110brefers to a partial area of the printedcircuit board110 including an area on which at least one of the plurality of MJT LEDs are mounted, upon mounting the plurality of MJT LEDs on the printedcircuit board110. Specifically, oneblock110bmay include at least one MJT LED. In an example, oneblock110bmay include only one MJT LED. However, the present disclosure is not limited thereto, but oneblock110bmay include a plurality of MJT LEDs.
• M blocks110bare disposed in a horizontal direction and N blocks110bare disposed in a vertical direction to form an M×N matrix arrangement. As shownFIG. 43B, for example, 45blocks110bmay constitute a 9×5 matrix arrangement. A horizontal length L1 of each of theblocks110bmay be 60 mm or less. In addition, a vertical length L2 of each of theblocks110bmay be 55 mm or less.
• In the exemplary embodiment shown inFIG. 2, it is assumed thatM MJT LEDs100 are disposed in a longitudinal direction andN MJT LEDs100 are disposed in a transverse direction to form an M×N matrix arrangement within thebacklight module300. In this case, the respective MJT LEDs may be disposed such that one MJT LED corresponds to one of the blocks (“one-to-one mapping configuration”). In addition, an MJT LED placed at a left side uppermost portion of the backlight module will be referred to as a 1-1st MJT LED (100_11) and an MJT LED placed at a right side lowermost portion thereof will be referred to as an M-Nth MJT LED (100_MN).
• Here, it should be noted that, unlike the related art shown inFIG. 1, theMJT LEDs100 within thebacklight module300 according to the embodiment ofFIG. 2 are independently connected to the operating power generator410 and theoperation controller420 instead of being connected to each other in series, in parallel, or in series/parallel. That is, in the embodiment shown inFIG. 2, an anode terminal of eachMJT LED100 is independently connected to the operating power generator410 and a cathode terminal of eachMJT LED100 is independently connected to theoperation controller420. When the respective MJT LEDs and the respective blocks correspond to each other with the one-to-one mapping configuration, the blocks may be configured to be independently connected to the operating power generator410 and the operatingcontroller420.
• With this configuration, theoperation controller420 according to this disclosure may independently control operation of each of the plurality ofMJT LEDs100 constituting thebacklight module300. More specifically, theoperation controller420 according to this disclosure may control a dimming level of a specific MJT LED among the plurality ofMJT LEDs100 in response to a dimming signal (Dim). When the respective MJT LEDs and the respective blocks correspond to each other with the one-to-one mapping configuration, the operatingcontroller420 may independently control an operation of each of the plurality of blocks.
• In one embodiment, theoperation controller420 according to the present disclosure includes a PWM (Pulse Width Modulation) controller (not shown) and may perform dimming control through pulse width modulation control with respect to operating power supplied to a specific MJT LED, which is a dimming control target, among theMJT LEDs100. Particularly, unlike the typical backlight unit in the related art as shown inFIG. 1, thebacklight unit1000 according to the present disclosure as shown inFIG. 2 includes the plurality ofMJT LEDs100, each of which is connected to the operating power generator410 to independently receive operating power, thereby enabling dimming control in such a pulse width modulation manner. Specifically, the operatingcontroller420 may control a duty ratio of operating power in the range of 0% to 100%. For example, when there is a need for dimming control of the 1-1st MJT LED (100_11), theoperation controller420 performs pulse width modulation of the generated operating power at a predetermined duty ratio (for example, 60%) in response to a dimming signal (Dim), and supplies the modified operating power to the 1-1st MJT LED (100_11) to perform dimming control of the 1-1st MJT LED (100_11). At this time, operating power, which is not subjected to pulse width modulation and has a duty ratio of 100%, will be supplied to other MJT LEDs except for the 1-1st MJT LED (100_11). Alternatively, operating power, which is subjected to pulse width modulation at a normal duty ratio (a duty ratio of, for example, 80% when no separate dimming control is provided), is provided to the other MJT LEDs except for the 1-1st MJT LED (100_11). Consequently, thebacklight unit1000 according to the present disclosure allows local dimming with respect to only the 1-1st MJT LED (100_11). Of course, it will be apparent to those skilled in the art that it is possible to perform simultaneous dimming control with respect to the plurality of MJT LEDs at the same dimming level and/or at different dimming levels for the respective MJT LEDs through PWM control. The operating power described above may be a DC operating voltage. The PWM controller for PWM control of the operating power is well known in the art, and thus, a detailed description thereof will be omitted.
• In another embodiment, theoperation controller420 according to the present disclosure includes an operating current detector (not shown) and an operating current controller (not shown), and may perform dimming control by controlling the operating current supplied to a specific MJT LED, which is a dimming control target, among theMJT LEDs100. Particularly, unlike the typical backlight unit shown inFIG. 1, in thebacklight unit1000 according to the present disclosure shown inFIG. 2, each of theplural MJT LEDs100 is independently connected to theoperation controller420, thereby enabling dimming control by control of the operating current of each of the MJT LEDs. Here, the operating current detector and the operating current controller included in theoperation controller420 correspond one to one to each of theMJT LEDs100. Accordingly, when thebacklight module300 is composed of M×N MJT LEDs100 as described above, theoperation controller420 includes M×N operating current detectors and M×N operating current controllers. For example, when there is a need for dimming control with respect to an M-Nth MJT LED (100_MN), theoperation controller420 detects operating current flowing through the M-Nth MJT LED (100_MN) using the operating current detector, and changes the operating current flowing through the M-Nth MJT LED (100_MN) (for example, to 100% of a maximum operating current) in response to a dimming signal (Dim), thereby performing dimming control with respect to the M-Nth MJT LED (100_MN). For example, the operatingcontroller420 may control the operation current in the range of 0% to 100%. Here, since normal operating current (a preset standard operating current, for example, 80% of the maximum operating current, when there is no separate dimming control) flows through other MJT LEDs except for the M-Nth MJT LED (100_MN), local dimming can be performed with respect only to the M-Nth MJT LED (100_MN). It will be apparent to those skilled in the art that dimming control of the plurality of MJT LEDs can be performed to the same dimming level through simultaneous control of the operating current with respect to the plurality of MJT LEDs and/or to different dimming levels for the respective MJT LEDs. In such an embodiment, since there is no need for independent supply of operating power to theMJT LEDs100, the anode terminal of each of theMJT LEDs100 may be connected in parallel to one operating power line connected to the operating power generator410, unlike the embodiment shown inFIG. 2. The operating current detector and the operating current controller are well known in the art and detailed descriptions thereof will thus be omitted.
• The operatingcontroller420 according to the present disclosure may include a plurality of switch controllers (not shown). The switch controllers may be each disposed between the plurality of MJT LEDs. Specifically, the switch controllers may be disposed between one MJT LED and an adjacent MJT LED. More specifically, the switch controllers may be disposed between one MJT LED and the remaining MJT LEDs. That is, the switch controllers may be disposed between one MJT LED of M×N MJT LEDs and the remaining M×N-1 MJT LEDs, which may correspond to all MJT LED included in thebacklight module300 as well as one MJT LED.
• The respective switch controllers may electrically connect two MJT LEDs connected by the switch controller, and may also electrically insulate the two MJT LEDs according to a switching operation. Thus, a plurality of MJT LEDs may be connected to each other in series and/or in parallel through the switch controllers. Consequently, a desired structure of thebacklight module300 may be easily implemented.
• The backlight unit according to the present disclosure may further include a floodlighting plate (not shown). The floodlighting plate may be disposed over thebacklight module300. Specifically, the floodlighting plate may be disposed over the printedcircuit board110 of thebacklight module300. The floodlighting plate may serve to diffuse light emitted from the MJT LEDs of thebacklight module300. A distance between a lower surface of the floodlighting plate and an upper surface of the printed circuit board may be 18 mm or more.
• Overview of MJT LED and MJT LED Module
• FIG. 3 is a schematic sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure, andFIG. 4 is a schematic perspective view of the MJT LED according to the one exemplary embodiment of the present disclosure. Now, detailed configurations of anMJT LED100 and an MJT LED module according to embodiments of the present disclosure will be described with reference toFIG. 3 andFIG. 4.
• Referring toFIG. 3, the MJT LED module includes anMJT LED100 and anoptical member130. When theMJT LED100 is mounted on a printedcircuit board110, the correspondingoptical member130 is mounted on the printedcircuit board110 at a place corresponding to the position of theMJT LED100. For example, each block of the printedcircuit board110 may include one optical member. As described above, in other embodiments, theoptical member130 may be directly connected to theMJT LED100. More specifically, theoptical member130 may be formed by molding a resin on the MJT LED. Although the printedcircuit board110 is partially shown inFIG. 3, a plurality ofMJT LEDs100 and theoptical members130 corresponding thereto are disposed on a single printedcircuit board110 in various arrangements such as a matrix arrangement or a honeycomb arrangement to form thebacklight module300 as described above.
• The printedcircuit board110 is formed on an upper surface thereof with conductive land patterns to which terminals of theMJT LED100 are bonded. Further, the printedcircuit board110 may include a reflective layer on the upper surface thereof. The printedcircuit board110 may be a MCPCB (Metal-Core PCB) based on a metal having good thermal conductivity. Alternatively, the printedcircuit board110 may be formed of an insulating substrate material such as FR4. Although not shown, the printedcircuit board110 may be provided at a lower side thereof with a heat sink to dissipate heat from theMJT LED100.
• As clearly shown inFIG. 4, theMJT LED100 may include ahousing121, anMJT LED chip123 mounted on thehousing121, and awavelength conversion layer125 covering theMJT LED chip123. The MJT LED100 further includes lead terminals (not shown) supported by thehousing121.
• Thehousing121 forms a package body and may be formed by injection molding of a plastic resin such as PA, PPA, and the like. In this case, thehousing121 may be formed in a state of supporting the lead terminals by an injection molding process, and may have acavity121afor mounting theMJT LED chip123 therein. Thecavity121adefines a light exit area of theMJT LED100.
• The lead terminals are separated from each other within thehousing121 and extend outside of thehousing121 to be bonded to the land patterns on the printedcircuit board110.
• TheMJT LED chip123 is mounted on the bottom of thecavity121aand electrically connected to the lead terminals. TheMJT LED chip123 may be a gallium nitride-based MJT LED which emits UV light or blue light. A detailed configuration of theMJT LED chip123 according to the present disclosure and a method of manufacturing the same will be described below with reference toFIG. 5 toFIG. 18.
• Thewavelength conversion layer125 covers theMJT LED chip123. In one embodiment, thewavelength conversion layer125 may be formed by filling thecavity121awith a molding resin containing phosphors after mounting theMJT LED chip123 in thecavity121a. At this time, thewavelength conversion layer125 may fill thecavity121aof thehousing121 and have a substantially flat or convex upper surface. Further, a molding resin having a shape of the optical member may be formed on thewavelength conversion layer125.
• In another embodiment, theMJT LED chip123, which has a coating layer of the phosphors formed by conformal coating, may be mounted on thehousing121. Specifically, the coating layer of the phosphors may be formed on theMJT LED chip123 by conformal coating and theMJT LED chip123 having the conformal coating layer may be mounted on thehousing121. TheMJT LED chip123 having the conformal coating layer may be molded with a transparent resin. In addition, the molding resin may have the shape of the optical member and thus may act as a primary optical member.
• Thewavelength conversion layer125 converts-wavelengths of light emitted from theMJT LED chip123 to provide light of mixed colors, for example, white light.
• Thewavelength conversion layer125 may include KSF-based and/or UCD-based phosphors. Thus, light emitted from theMJT LED chip123 to penetrate through thewavelength conversion layer125 may have an NTSC color reproduction ratio of 70% or more.
• TheMJT LED100 is designed to have a light beam distribution of a mirror symmetry structure, particularly, a light beam distribution of a rotational symmetry structure. At this time, an axis of the MJT LED directed towards the center of the light beam distribution is defined as an optical axis L. That is, theMJT LED100 is designed to have a light beam distribution which is bilaterally symmetrical with respect to the optical axis L. Generally, thecavity121aof thehousing121 may have a mirror symmetry structure, and the optical axis L may be defined as a straight line passing through the center of thecavity121a.
• Theoptical member130 includes a light incident face through which light emitted from theMJT LED100 enters the optical member and a light exit face through which the light exits the optical member at a wider light beam distribution than that of theMJT LED100, thereby enabling uniform distribution of the light emitted fromMJT LED100. Theoptical member130 according to the present disclosure will be described below with reference toFIG. 19A toFIG. 33B.
• Configuration of MJT LED Chip and Method of Manufacturing the Same
• Next, the configuration of theMJT LED chip123 mounted on the MJT LED according to the present disclosure and a method of manufacturing the same will be described in more detail with reference toFIG. 5 toFIG. 18.
• FIG. 5 is a schematic plan view of an MJT LED chip according to one exemplary embodiment of the present disclosure, andFIG. 6 is a schematic sectional view of the MJT LED chip taken along line B-B ofFIG. 5.
• Referring toFIG. 5 andFIG. 6, theMJT LED chip123 includes agrowth substrate51, light emitting cells S1, S2, atransparent electrode layer61, acurrent blocking layer60a, aninsulation layer60b, an insulationprotective layer63, and aninterconnection line65. Further, theMJT LED chip123 may include abuffer layer53.
• Thegrowth substrate51 may be an insulation or conductive substrate, and may include, for example, a sapphire substrate, a gallium nitride substrate, a silicon carbide (SiC) substrate, or a silicon substrate. In addition, thegrowth substrate51 may have a convex-concave pattern (not shown) on an upper surface thereof as in a patterned sapphire substrate.
• A first light emitting cell S1 and a second light emitting cell S2 are separated from each other on asingle growth substrate51. Each of the first and second light emitting cells S1, S2 has astack structure56, which includes alower semiconductor layer55, anupper semiconductor layer59 placed on a region of the lower semiconductor layer, and anactive layer57 interposed between the lower semiconductor layer and the upper semiconductor layer. Here, the upper and lower semiconductor layers may be an n-type semiconductor layer and a p-type semiconductor layer, respectively, or vice versa.
• Each of thelower semiconductor layer55, theactive layer57 and theupper semiconductor layer59 may be formed of a gallium nitride-based semiconductor material, that is, (Al, In, Ga)N. The compositional elements and ratio of theactive layer57 are determined depending upon desired wavelengths of light, for example, UV light or blue light, and thelower semiconductor layer55 and theupper semiconductor layer59 are formed of a material having a greater band gap than theactive layer57.
• Thelower semiconductor layer55 and/or theupper semiconductor layer59 may have a single layer structure, as shown inFIG. 5. Alternatively, these semiconductor layers may have a multilayer structure. Further, theactive layer57 may have a single quantum-well structure or a multi-quantum well structure.
• MN Each of the first and second light emitting cells S1, S2 may have a slanted side surface, an inclination of which may range, for example, from 15° to 80° relative to an upper surface of thegrowth substrate51.
• Theactive layer57 and theupper semiconductor layer59 are placed on thelower semiconductor layer55. An upper surface of thelower semiconductor layer55 may be completely covered by theactive layer57 such that only a side surface thereof is exposed.
• Although portions of the first light emitting cell S1 and the second light emitting cell S2 are shown inFIG. 6, the first and second light emitting cells S1, S2 may have a similar or the same structure as that shown inFIG. 5. That is, the first light emitting cell S1 and the second light emitting cell S2 may have the same gallium nitride-based semiconductor stack structure, and may have slanted side surfaces of the same structure.
• Thebuffer layer53 may be interposed between the light emitting cells S1, S2 and thegrowth substrate51. Thebuffer layer53 relieves lattice mismatch between thegrowth substrate51 and thelower semiconductor layer55 formed thereon.
• Thetransparent electrode layer61 is placed on each of the light emitting cells S1, S2. That is, a firsttransparent electrode layer61 is placed on the first light emitting cell S1 and a secondtransparent electrode layer61 is placed on the second light emitting cell S2. Thetransparent electrode layer61 may be placed on theupper semiconductor layer59 to be connected to theupper semiconductor layer59, and may have a narrower area than theupper semiconductor layer59. That is, thetransparent electrode layer61 may be recessed from an edge of theupper semiconductor layer59. With this structure, it is possible to prevent current crowding at the edge of thetransparent electrode layer61 through the side surfaces of the light emitting cells S1, S2.
• In another aspect, thecurrent blocking layer60amay be placed on each of the light emitting cells S1, S2. That is, thecurrent blocking layer60ais placed between thetransparent electrode layer61 and each of the light emitting cells S1, S2. Part of thetransparent electrode layer61 is placed on thecurrent blocking layer60a. Thecurrent blocking layer60amay be placed near an edge of each of the light emitting cells S1, S2, but is not limited thereto. Alternatively, thecurrent blocking layer60amay be placed in a central region of each of the light emitting cells S1, S2. Thecurrent blocking layer60ais formed of an insulation material and, particularly, may include a distributed Bragg reflector in which layers having different indices of refraction are alternately stacked one above another.
• Theinsulation layer60bcovers a portion of the side surface of the first light emitting cell S1. As shown inFIG. 5 andFIG. 6, theinsulation layer60bmay extend to a region between the first light emitting cell S1 and the second light emitting cell S2, and may cover a portion of a side surface of thelower semiconductor layer55 of the second light emitting cell S2. Theinsulation layer60bmay have the same structure and the same material as those of thecurrent blocking layer60a, and may include a distributed Bragg reflector, without being limited thereto. Theinsulation layer60bmay be formed of a different material than that of thecurrent blocking layer60aby a different process. Here, when theinsulation layer60bis a distributed Bragg reflector formed by stacking multiple layers, it is possible to efficiently suppress generation of defects such as pinholes in theinsulation layer60b. Theinsulation layer60bmay be connected to thecurrent blocking layer60ato form continuous layers, but is not limited thereto. In other embodiments, theinsulation layer60bmay be separated from thecurrent blocking layer60a.
• Theinterconnection line65 electrically connects the first light emitting cell S1 to the second light emitting cell S2. Theinterconnection line65 includes afirst connection section65pand asecond connection section65n. Thefirst connection section65pis electrically connected to thetransparent electrode layer61 on the first light emitting cell S1, and thesecond connection section65nis electrically connected to thelower semiconductor layer55 of the second light emitting cell S2. Thefirst connection section65pmay be placed near one edge of the first light emitting cell S1, but is not limited thereto. In other embodiments, thefirst connection section65pmay be placed in the central region of the first light emitting cell S1.
• Thesecond connection section65nmay contact the slanted side surface of the second light emitting cell S2, particularly, the slanted side surface of thelower semiconductor layer55 of the second light emitting cell S2. Further, as shown inFIG. 5, thesecond connection section65nmay electrically contact the slanted side surface of thelower semiconductor layer55 while extending to both sides along the circumference of the second light emitting cell S2. The first light emitting cell S1 is connected to the second light emitting cell S2 in series by the first andsecond connection sections65p,65nof theinterconnection line65.
• Theinterconnection line65 may contact thetransparent electrode layer61 over an overlapping region with thetransparent electrode layer61. In the related art, a portion of the insulation layer is placed between the transparent electrode layer and the interconnection line. On the contrary, according to the present disclosure, theinterconnection line65 may directly contact thetransparent electrode layer61 without any insulation material interposed therebetween.
• Further, thecurrent blocking layer60amay be placed over the overlapping region between theinterconnection line65 and thetransparent electrode layer61, and thecurrent blocking layer60aand theinsulation layer60bmay be placed over an overlapping region between theinterconnection line65 and the first light emitting cell S1. Further, theinsulation layer60bmay be placed between the second light emitting cell S2 and theinterconnection line65 in other regions excluding a connection region between theinterconnection line65 and the second light emitting cell S2.
• InFIG. 5, thefirst connection section65pand thesecond connection section65nof theinterconnection line65 are connected to each other through two paths. However, it should be understood that the first and second connection sections may be connected to each other via a single path.
• When thecurrent blocking layer60aand theinsulation layer60bhave reflective characteristics like the distributed Bragg reflector, thecurrent blocking layer60aand theinsulation layer60bare preferably placed substantially in the same region as the region for theinterconnection line65 within a region having an area of two times or less the area of theinterconnection line65. Thecurrent blocking layer60aand theinsulation layer60bblock light emitted from theactive layer57 from being absorbed into theinterconnection line65. However, when occupying an excessively large area, thecurrent blocking layer60aand theinsulation layer60bcan block emission of light to the outside. Thus, there is a need for restriction of the area thereof.
• The insulationprotective layer63 may be placed outside the region of theinterconnection line65. The insulationprotective layer63 covers the first and second light emitting cells S1, S2 outside the region of theinterconnection line65. The insulationprotective layer63 may be formed of silicon oxide (SiO₂) or silicon nitride. The insulationprotective layer63 has an opening through which thetransparent electrode layer61 on the first light emitting cell S1 and the lower semiconductor layer of the second light emitting cell S2 are exposed, and theinterconnection line65 may be placed within the opening.
• A side surface of the insulationprotective layer63 and a side surface of theinterconnection line65 may face each other, and may contact each other. Alternatively, the side surface of the insulationprotective layer63 and the side surface of theinterconnection line65 may be separated from each other while facing each other.
• According to the present embodiment, since thesecond connection section65nof theinterconnection line65 electrically contacts the slanted side surface of the second light emitting cell S2, there is no need to expose the upper surface of thelower semiconductor layer55 of the second light emitting cell S2. Accordingly, there is no need for partial removal of thesecond semiconductor layer59 and theactive layer57, thereby increasing an effective light emitting area of theMJT LED chip123.
• In addition, thecurrent blocking layer60aand theinsulation layer60bmay be formed of the same material and have the same structure, and thus may be formed at the same time by the same process. Further, since theinterconnection line65 is placed within the opening of the insulationprotective layer63, the insulationprotective layer63 and theinterconnection line65 may be formed using the same mask pattern.
• Although two light emitting cells including the first light emitting cell S1 and the second light emitting cell S2 are illustrated in this embodiment, it should be understood that the present disclosure is not limited thereto. That is, a greater number of light emitting cells may be electrically connected to each other via the interconnection lines65. For example, theinterconnection lines65 may electrically connect the lower semiconductor layers55 and the transparent electrode layers61 of adjacent light emitting cells to each other to form a series array of light emitting cells. A plurality of such arrays may be formed and connected in inverse-parallel to each other to be operated by an AC power source connected thereto. In addition, a bridge rectifier (not shown) may be connected to the series array of light emitting cells to allow the light emitting cells to be operated by the AC power source. The bridge rectifier may be formed by bridging the light emitting cells having the same structure as that of the light emitting cells S1, S2 using the interconnection lines65.
• FIG. 7 toFIG. 13 are schematic sectional views illustrating a method of fabricating an MJT LED chip according to one exemplary embodiment of the present disclosure.
• Referring toFIG. 7, asemiconductor stack structure56 including alower semiconductor layer55, anactive layer57 and anupper semiconductor layer59 is formed on agrowth substrate51. In addition, abuffer layer53 may be formed on thegrowth substrate51 before formation of thelower semiconductor layer55.
• Thegrowth substrate51 may be formed of a material selected from among sapphire (Al₂O₃), silicon carbide (SiC), zinc oxide (ZnO), silicon (Si), gallium arsenic (GaAs), gallium phosphide (GaP), lithium alumina (LiAl₂O₃), boron nitride (BN), aluminum nitride (AlN), and gallium nitride (GaN), without being limited thereto. That is, the material for thegrowth substrate51 may be selected in various ways depending upon materials of semiconductor layers to be formed on thegrowth substrate51. Further, thegrowth substrate51 may have a convex-concave pattern on an upper surface thereof as in a patterned sapphire substrate.
• Thebuffer layer53 is formed to relieve lattice mismatch between thegrowth substrate51 and thesemiconductor layer55 formed thereon, and may be formed of, for example, gallium nitride (GaN) or aluminum nitride (AlN). When thegrowth substrate51 is a conductive substrate, thebuffer layer53 is preferably formed of an insulation layer or a semi-insulating layer. For example, thebuffer layer53 may be formed of AlN or semi-insulating GaN.
• Each of thelower semiconductor layer55, theactive layer57 and theupper semiconductor layer59 may be formed of a gallium nitride-based semiconductor material, for example, (Al, In, Ga)N. The lower and upper semiconductor layers55,59 and theactive layer57 may be intermittently or continuously formed by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy, hydride vapor phase epitaxy (HVPE), and the like.
• Here, the lower and upper semiconductor layers may be n-type and p-type semiconductor layers, or vice versa. Among the gallium nitride-based compound semiconductor layers, an n-type semiconductor layer may be formed by doping an n-type impurity, for example, silicon (Si), and a p-type semiconductor layer may be formed by doping a p-type impurity, for example, magnesium (Mg).
• Referring toFIG. 8, a plurality of light emitting cells S1, S2 separated from each other is formed by a photolithography and etching process. Each of the light emitting cells S1, S2 is formed to have a slanted side surface. In a typical method of manufacturing an MJT LED chip, an additional photolithography and etching process is performed to partially expose an upper surface of thelower semiconductor layer55 of each of the light emitting cells S1, S2. However, in this embodiment, the photolithography and etching process performed to partially expose the upper surface of thelower semiconductor layer55 is omitted.
• Referring toFIG. 9, acurrent blocking layer60acovering some region on the first light emitting cell S1 and aninsulation layer60bpartially covering the side surface of the first light emitting cell S1 are formed. Theinsulation layer60bmay extend to cover a region between the first light emitting cell S1 and the second light emitting cell S2 while partially covering a side surface of thelower semiconductor layer55 of the second light emitting cell S2.
• Thecurrent blocking layer60aand theinsulation layer60bmay be formed by depositing an insulation material layer, followed by patterning through photolithography and etching. Alternatively, thecurrent blocking layer60aand theinsulation layer60bmay be formed of an insulation material layer by a lift-off technique. Particularly, each of thecurrent blocking layer60aand theinsulation layer60bmay be a distributed Bragg reflector formed by alternately stacking layers having different indices of refraction, for example, SiO₂and TiO₂layers. When theinsulation layer60bis a distributed Bragg reflector formed by stacking multiple layers, it is possible to efficiently suppress generation of defects such as pinholes in theinsulation layer60b, whereby theinsulation layer60bcan be formed to a smaller thickness than in the related art.
• As shown inFIG. 9, thecurrent blocking layer60aand theinsulation layer60bmay be connected to each other. However, it should be understood that the present disclosure is not limited thereto.
• Then, atransparent electrode layer61 is formed on the first and second light emitting cells S1, S2. Thetransparent electrode layer61 may be formed of an indium tin oxide (ITO) layer, a conductive oxide layer such as a zinc oxide layer, or a metal layer such as Ni/Au. Thetransparent electrode layer61 is connected to theupper semiconductor layer59 and is partially placed on thecurrent blocking layer60a. Thetransparent electrode layer61 may be formed by a lift-off process, without being limited thereto. Alternatively, thetransparent electrode layer61 may be formed by a photolithography and etching process.
• Referring toFIG. 10, an insulationprotective layer63 is formed to cover the first and second light emitting cells S1, S2. The insulationprotective layer63 covers thetransparent electrode layer61 and theinsulation layer60b. In addition, the insulationprotective layer63 may cover an overall area of the first and second light emitting cells S1, S2. The insulationprotective layer63 may be formed of an insulation material layer, such as a silicon oxide or silicon nitride layer, by chemical vapor deposition.
• Referring toFIG. 11, amask pattern70 having an opening is formed on the insulationprotective layer63. The opening of themask pattern70 corresponds to a region for an interconnection line. Then, some region of the insulationprotective layer63 is removed by etching through themask pattern70. As a result, an opening is formed on the insulationprotective layer63 to expose some of thetransparent electrode layer61 and theinsulation layer60bwhile exposing the slanted side surface of thelower semiconductor layer55 of the second light emitting cell S2.
• Referring toFIG. 12, with themask pattern70 remaining on the insulationprotective layer63, a conductive material is deposited to form theinterconnection line65 within the opening of themask pattern70. Here, some of theconductive material65amay be deposited on themask pattern70. The conductive material may be deposited by plating, e-beam evaporation, sputtering, and the like.
• Referring toFIG. 11, themask pattern70, together with some of theconductive material65a, is removed from themask pattern70. As a result, theinterconnection line65 electrically connecting the first and second light emitting cells S1, S2 to each other is completed.
• Here, afirst connection section65pof theinterconnection line65 is connected to thetransparent electrode layer61 of the first light emitting cell S1, and asecond connection section65nthereof is connected to the slanted side surface of thelower semiconductor layer55 of the second light emitting cell S2. Thefirst connection section65pof theinterconnection line65 may be connected to thetransparent electrode layer60awithin an upper region of thecurrent blocking layer60a. Theinterconnection line65 is separated from the side surface of the first light emitting cell S1 by theinsulation layer60b.
• In this embodiment, thecurrent blocking layer60aand theinsulation layer60bare formed by the same process. As a result, the insulationprotective layer63 and theinterconnection line65 may be formed using thesame mask pattern70, whereby the MJT LED chip can be manufactured by the same number of exposure processes while adding thecurrent blocking layer60a.
• FIG. 14 is a schematic sectional view of an MJT LED chip according to another exemplary embodiment of the present disclosure.
• Referring toFIG. 14, the MJT LED chip according to this embodiment is generally similar to the MJT LED chip described with reference toFIGS. 5 and 6, and further includes a transparentconductive layer62.
• Thegrowth substrate51, the light emitting cells S1, S2, thebuffer layer53, thetransparent electrode layer61, thecurrent blocking layer60a, theinsulation layer60b, the insulationprotective layer63 and theinterconnection line65 are similar to those of the light emitting diode described with reference toFIGS. 5 and 6, and thus detailed descriptions thereof will be omitted.
• The transparentconductive layer62 is placed between theinsulation layer60band theinterconnection line65. The transparentconductive layer62 has a narrower width than theinsulation layer60b, thereby preventing a short circuit of theupper semiconductor layer59 and thelower semiconductor layer55 due to the transparentconductive layer62.
• On the other hand, the transparentconductive layer62 is connected to a firsttransparent electrode layer61, and may electrically connect the firsttransparent electrode layer61 to the second light emitting cell S2. For example, the transparentconductive layer62 may be connected at one end thereof to thelower semiconductor layer55 of the second light emitting cell. In addition, when two or more light emitting cells are connected thereto, a second transparentconductive layer62 may extend from a secondtransparent electrode layer61 on the second light emitting cell S2.
• In this embodiment, since the transparentconductive layer62 is placed between theinterconnection line65 and theinsulation layer60b, current can flow through the transparentconductive layer62 even in the case where theinterconnection line65 is disconnected, thereby improving electric stability of the MJT LED chip.
• FIG. 15 toFIG. 18 are schematic sectional views illustrating a method of fabricating an MJT LED chip according to another exemplary embodiment of the present disclosure.
• Referring toFIG. 15, first, as described with reference toFIGS. 7 and 8, asemiconductor stack structure56 is formed on agrowth substrate51, and a plurality of light emitting cells S1, S2 separated from each other is formed by a photolithography and etching process. Then, as described with reference toFIG. 9, acurrent blocking layer60acovering a region on the first light emitting cell S1 and aninsulation layer60bpartially covering a side surface of the first light emitting cell S1 are formed.
• As described with reference toFIG. 9, each of thecurrent blocking layer60aand theinsulation layer60bmay include a distributed Bragg reflector formed by alternately stacking layers having different indices of refraction, for example, SiO₂and TiO₂layers. When theinsulation layer60binclude the distributed Bragg reflector formed by stacking multiple layers, it is possible to efficiently suppress generation of defects such as pinholes in theinsulation layer60b, whereby theinsulation layer60bcan be formed to a smaller thickness than in the related art.
• Then, atransparent electrode layer61 is formed on the first and second light emitting cells S1, S2. As described with reference toFIG. 9, thetransparent electrode layer61 may be formed of an indium tin oxide (ITO) layer, a conductive oxide layer such as a zinc oxide layer, or a metal layer such as Ni/Au. Thetransparent electrode layer61 is connected to theupper semiconductor layer59 and is partially placed on thecurrent blocking layer60a. Thetransparent electrode layer61 may be formed by a lift-off process, without being limited thereto. Alternatively, thetransparent electrode layer61 may be formed by a photolithography and etching process.
• During formation of thetransparent electrode layer61, a transparentconductive layer62 is formed. The transparentconductive layer62 may be formed together with thetransparent electrode layer61 using the same material and the same process. The transparentconductive layer62 is formed on theinsulation layer60band may be connected to thetransparent electrode layer61. Further, the transparentconductive layer62 may be electrically connected at one end thereof to the slanted side surface of thelower semiconductor layer55 of the second light emitting cell S2.
• Referring toFIG. 16, an insulationprotective layer63 is formed to cover the first and second light emitting cells S1, S2. The insulationprotective layer63 covers thetransparent electrode layer61, the transparentconductive layer62, and theinsulation layer60b. In addition, the insulationprotective layer63 may cover an overall area of the first and second light emitting cells S1, S2. The insulationprotective layer63 may be formed of an insulation material layer, such as silicon oxide or silicon nitride, by chemical vapor deposition.
• Referring toFIG. 17, as described with reference toFIG. 11, amask pattern70 having an opening is formed on the insulationprotective layer63. The opening of themask pattern70 corresponds to a region for an interconnection line. Then, a portion of the insulationprotective layer63 is removed by etching through themask pattern70. As a result, an opening is formed on the insulationprotective layer63 to expose some of thetransparent electrode layer61 and the transparentconductive layer62, while exposing the slanted side surface of thelower semiconductor layer55 of the second light emitting cell S2. Further, theinsulation layer60bis partially exposed through the opening.
• Referring toFIG. 18, as described with reference toFIG. 12, with themask pattern70 remaining on the insulationprotective layer63, a conductive material is deposited to form aninterconnection line65 within the opening of themask pattern70.
• Then, referring toFIG. 13, themask pattern70, together with some of theconductive material65a, is removed from themask pattern70. As a result, theinterconnection line65 electrically connecting the first and second light emitting cells S1, S2 to each other is completed.
• In the embodiments described with reference toFIG. 7 toFIG. 13, theinsulation layer60bcan be damaged during etching of the insulationprotective layer63. For example, when the insulationprotective layer63 is subjected to etching using an etchant, which contains, for example, hydrofluoric acid, theinsulation layer60bincluding an oxide layer can be damaged by the etchant. In this case, theinsulation layer60bcan fail to insulate theinterconnection line65 from the first light emitting cell S1, thereby causing a short circuit.
• However, in the present embodiment, since the transparentconductive layer62 is placed on theinsulation layer60b, theinsulation layer60bunder the transparentconductive layer62 can be protected from etching damage. As a result, it is possible to prevent a short circuit due to theinterconnection line65.
• In this embodiment, thetransparent electrode layer61 and the transparentconductive layer62 may be formed by the same process. Accordingly, the MJT LED chip can be manufactured by the same number of exposing processes while adding the transparentconductive layer62.
• FIG. 34 is a schematic sectional view of an MJT LED chip according to another exemplary embodiment of the present disclosure, andFIG. 35 is a cross-sectional view of the MJT LED chip taken along section B-B ofFIG. 34.
• Referring toFIG. 34 andFIG. 35, theMJT LED chip123 includes agrowth substrate51, light emitting cells S1, S2, transparent electrode layers61,62, aninsulation layer60b, an insulationprotective layer63, and aninterconnection line65. Further, theMJT LED chip123 may include abuffer layer53. Further, theMJT LED chip123 may include acurrent blocking layer60a.
• Thegrowth substrate51 may be an insulation or conductive substrate, and may be, for example, a sapphire substrate, a gallium nitride substrate, a silicon carbide (SiC) substrate, or a silicon substrate. In addition, thegrowth substrate51 may have a convex-concave pattern (not shown) on an upper surface thereof as in a patterned sapphire substrate. The convex-concave pattern may serve to effectively reflect light toward the growth substrate among lights emitted from the light emitting cells to improve light extraction efficiency.
• A first light emitting cell S1 and a second light emitting cell S2 are disposed on asingle growth substrate51 to be spaced apart from each other. Each of the first and second light emitting cells S1, S2 has astack structure56, which includes alower semiconductor layer55, anupper semiconductor layer59 disposed on a region of thelower semiconductor layer55, and anactive layer57 interposed between thelower semiconductor layer55 and theupper semiconductor layer59. Here, the upper and lower semiconductor layers may be an n-type semiconductor layer and a p-type semiconductor layer, respectively, or vice versa.
• Each of thelower semiconductor layer55, theactive layer57 and theupper semiconductor layer59 may be formed of a gallium nitride-based semiconductor material, that is, (Al, In, Ga)N. The compositional elements and ratio of theactive layer57 are determined depending upon desired wavelengths of light, for example, UV light or blue light, and thelower semiconductor layer55 and theupper semiconductor layer59 are formed of a material having a greater band gap than theactive layer57.
• Thelower semiconductor layer55 and/or theupper semiconductor layer59 may have a single layer structure, as illustrated. Alternatively, these semiconductor layers may have a multilayer structure. Further, theactive layer57 may have a single quantum-well structure or a multi-quantum well structure.
• Each of the first and second light emitting cells S1, S2 may have a slanted side surface having an inclination of which may range, for example, from 15° to 80° relative to an upper surface of thegrowth substrate51.
• Theactive layer57 and theupper semiconductor layer59 are disposed on thelower semiconductor layer55. At least a portion of an upper surface of thelower semiconductor layer55 may be covered by theactive layer57, and the remaining portions thereof may not be covered by theactive layer57, but be exposed. For example, as shown inFIG. 6 andFIG. 35, the upper surface of thelower semiconductor layer55 may include an exposed region R. The exposed region R is a region, which is not covered by theactive layer57 and theupper semiconductor layer59, but in which a portion of thelower semiconductor layer55, specifically, the upper surface of thelower semiconductor layer55 is exposed. The exposed region R may be disposed to be in parallel to a side surface which is directed to an adjacent light emitting cell, among side surfaces of thelower semiconductor layer55. However, the position of the exposed region R is not limited thereto, but may also be disposed to surround at least a portion of theactive layer57 and theupper semiconductor layer59.
• Although portions of the first light emitting cell S1 and the second light emitting cell S2 are shown inFIG. 35, the first and second light emitting cells S1, S2 may have a similar or the same structure as the first and second light emitting cells S1, S2 shown inFIG. 34. That is, the first light emitting cell S1 and the second light emitting cell S2 may have the same gallium nitride-based semiconductor stack structure, and may have slanted side surfaces of the same structure.
• Thebuffer layer53 may be interposed between the light emitting cells S1, S2 and thegrowth substrate51. Thebuffer layer53 is adopted to alleviate lattice mismatch between thegrowth substrate51 and thelower semiconductor layer55 formed thereon.
• The transparent electrode layers61,62 are disposed on each of the light emitting cells S1, S2. More specifically, a firsttransparent electrode layer61 is disposed on the first light emitting cell S1 and a secondtransparent electrode layer62 is disposed on the second light emitting cell S2. The transparent electrode layers61,62 may be disposed on the upper surface of theupper semiconductor layer59 to be connected to theupper semiconductor layer59, and may have a narrower area than theupper semiconductor layer59. That is, the transparent electrode layers61,62 may be recessed from an edge of theupper semiconductor layer59. With this structure, it is possible to prevent or reduce current crowding at the edges of the transparent electrode layers61,62 through the side surfaces of the light emitting cells S1, S2.
• A portion of the firsttransparent electrode layer61 may be connected to the second light emitting cell S2. Specifically, the portion of the firsttransparent electrode layer61 may be disposed on the first light emitting cell S1, between the first light emitting cell S1 and the second light emitting cell S2, and on the side surface of thelower semiconductor layer55 of the second light emitting cell S2. Thus, also in the case in which theinterconnection line65 is short-circuited, the current may flow through the firsttransparent electrode layer61, thereby improving electrical stability of the MJT LED chip. Further, the firsttransparent electrode layer61 may be further extended to be disposed on the exposed region R of the upper surface of thelower semiconductor layer55. The firsttransparent electrode layer61 may be spaced apart from theactive layer57 and theupper semiconductor layer59 of the second light emitting cell S2.
• Theinsulation layer60bcovers a portion of the side surface of the first light emitting cell S1. As shown inFIG. 34 andFIG. 35, theinsulation layer60bmay extend to a region between the first light emitting cell S1 and the second light emitting cell S2, and may cover a portion of a side surface of thelower semiconductor layer55 of the second light emitting cell S2. Theinsulation layer60bmay be formed of an insulating material, and may particularly include a distributed Bragg reflector in which layers having different reflective indexes are alternately stacked. However, theinsulation layer60bis not limited thereto. When theinsulation layer60bincludes a distributed Bragg reflector, which is multiple layers, it is possible to efficiently suppress generation of defects such as pinholes in theinsulation layer60b.
• Theinterconnection line65 electrically connects the first light emitting cell S1 to the second light emitting cell S2. Theinterconnection line65 includes afirst connection section65pand asecond connection section65n. Thefirst connection section65pis electrically connected to thetransparent electrode layer61 on the first light emitting cell S1, and thesecond connection section65nis electrically connected to thelower semiconductor layer55 of the second light emitting cell S2. Thefirst connection section65pmay be disposed near one edge of the first light emitting cell S1, but is not limited thereto. In other embodiments, thefirst connection section65pmay be disposed in the central region of the first light emitting cell S1.
• Thesecond connection section65nmay be electrically connected to thelower semiconductor layer55 of the second light emitting cell S2. Specifically, thesecond connection section65nmay be electrically connected to the upper surface of thelower semiconductor layer55 of the second light emitting cell S2 through the exposed region R. Further, the firsttransparent electrode layer61 may be disposed between thesecond connection section65nand thelower semiconductor layer55 of the second light emitting cell S2. In this case, the firsttransparent electrode layer61 may be disposed on a side surface of thelower semiconductor layer55 of the second light emitting cell S2, and may also be disposed on the exposed region R of thelower semiconductor layer55.
• Thesecond connection section65nmay contact the slanted side surface of the second light emitting cell S2, more particularly, the slanted side surface of thelower semiconductor layer55 of the second light emitting cell S2. Further, as shown inFIG. 34, thesecond connection section65nmay electrically contact the slanted side surface of thelower semiconductor layer55 while extending to both sides along the circumference of the second light emitting cell S2. The first light emitting cell S1 is connected to the second light emitting cell S2 in series by the first andsecond connection sections65p,65nof theinterconnection line65.
• Theinterconnection line65 may contact the transparent electrode layers61,62 over an overlapping region with the transparent electrode layers61,62. In the related art, a portion of the insulation layer is disposed between a transparent electrode layer and an interconnection line. However, according to an exemplary embodiment of the present disclosure, theinterconnection line65 may directly contact the transparent electrode layers61,62 without any insulation material interposed therebetween.
• With respect to the width of theinterconnection line65, the width of a portion of the firsttransparent electrode layer61 disposed on the side surface of thelower semiconductor layer55 of the second light emitting cell S2 may be wider than that of a portion of theinterconnection line65 disposed on the side surface of thelower semiconductor layer55 of the second light emitting cell S2. Thus, since a current in a region in which the side surface of the second light emitting cell S2 and theinterconnection line65 contact may be easily distributed, light emitting uniformity of the MJT LED chip may be improved.
• Further, the width of a portion of the firsttransparent electrode layer61 disposed between the first light emitting cell S1 and the second light emitting cell S2 may be wider than that of a portion of theinterconnection line65 disposed between the first light emitting cell S1 and the second light emitting cell S2. In general, when the insulationprotective layer63 is etched using an etchant such as hydrofluoric acid, theinsulation layer60bincluding an oxide layer may be damaged by the etchant. In this case, since theinsulation layer60bdoes not insulate theinterconnection line65 from the first light emitting cell S1, a short-circuit may occur. On the other hand, according to an exemplary embodiment of the present disclosure, since the firsttransparent electrode layer61 is disposed on theinsulation layer60b, and the width of the portion of the firsttransparent electrode layer61 disposed between the first light emitting cell S1 and the second light emitting cell S2 is wider than that of the portion of theinterconnection line65 disposed between the first light emitting cell S1 and the second light emitting cell S2, theinsulation layer60bdisposed below a transparentconductive layer62 may be protected from etching damage. Thus, the short-circuit problem by theinterconnection line65 is prevented.
• InFIG. 34, thefirst connection section65pand thesecond connection section65nof theinterconnection line65 are connected to each other through two paths. However, it should be understood that the first and second connection sections may be connected to each other via a single path or more than two paths.
• When theinsulation layer60bhas reflective characteristics like the distributed Bragg reflector, theinsulation layer60bmay be disposed substantially in the same region as the region for theinterconnection line65 within a region having an area of two times or less the area of theinterconnection line65. Theinsulation layer60bblocks light emitted from theactive layer57 from being absorbed into theinterconnection line65. However, when occupying an excessively large area, theinsulation layer60bcan block emission of light to the outside. Thus, there is a need for restriction of the area thereof.
• The insulationprotective layer63 may be disposed outside the region of theinterconnection line65. The insulationprotective layer63 covers the first and second light emitting cells S1, S2 outside the region of theinterconnection line65. The insulationprotective layer63 may be formed of silicon oxide (SiO₂) or silicon nitride. The insulationprotective layer63 has an opening through which thetransparent electrode layer61 on the first light emitting cell S1 and the lower semiconductor layer of the second light emitting cell S2 are exposed, and theinterconnection line65 may be disposed within the opening.
• A side surface of the insulationprotective layer63 and a side surface of theinterconnection line65 may face each other, and may also contact each other. One side surface of the insulationprotective layer63 may be disposed on the exposed region R and may contact the side surface of theinterconnection line65. Unlike this, the side surface of the insulationprotective layer63 and the side surface of theinterconnection line65 may be spaced apart from each other while facing each other.
• According to the present embodiment, since thesecond connection section65nelectrically contacts the upper surface of thelower semiconductor layer55, that is, a surface which is not slanted, thesecond connection section65ndisposed on the upper surface of thelower semiconductor layer55 may have a uniform thickness, Thus, reliability of the interconnection line may be improved. In addition, since the insulationprotective layer63 contacts theinterconnection line65 on the upper surface of thelower semiconductor layer55 which is not slanted with the side surface of the lower semiconductor layer of the second light emitting cell S2, an area of an interface between the insulationprotective layer63 and theinterconnection line65 may be substantially constant. Thus, an error rate of the MJT LED may be reduced.
• In addition, thecurrent blocking layer60aand theinsulation layer60bmay be formed of the same material and have the same structure, and thus may be formed at the same time by the same process. Further, since theinterconnection line65 is disposed within the opening of the insulationprotective layer63, the insulationprotective layer63 and theinterconnection line65 may be formed using the same mask pattern.
• Although two light emitting cells including the first light emitting cell S1 and the second light emitting cell S2 are illustrated in this exemplary embodiment, it should be understood that the present disclosure is not limited thereto. Specifically, a greater number of light emitting cells may be electrically connected to each other via the interconnection lines65. For example, theinterconnection lines65 may electrically connect the lower semiconductor layers55 and the transparent electrode layers61 of adjacent light emitting cells to each other to form a series array of light emitting cells. A plurality of such arrays may be formed and connected inversely parallel to each other to be operated by an AC power source connected thereto. In addition, a bridge rectifier (not shown) may be connected to the series array of light emitting cells to allow the light emitting cells to be operated by the AC power source. The bridge rectifier may be formed by bridging the light emitting cells having the same structure as that of the light emitting cells S1, S2 using the interconnection lines65.
• As the number of light emitting cells within each of the MJT LEDs is increased, an area of each of blocks of the printed circuit board may be decreased. Thus, the backlight unit capable of implementing various light emitting arrangements by the plurality of MJT LEDs while reducing a droop phenomenon by more light emitting cells may be provided.
• FIG. 36 throughFIG. 42 are cross-sectional views illustrating a method of fabricating anMJT LED chip123 according to one exemplary embodiment of the present disclosure.
• Referring toFIG. 36, asemiconductor stack structure56 including alower semiconductor layer55, anactive layer57 and anupper semiconductor layer59 is formed on agrowth substrate51. In addition, abuffer layer53 may be formed on thegrowth substrate51 before the formation of thelower semiconductor layer55.
• Thegrowth substrate51 may be sapphire (Al₂O₃), silicon carbide (SiC), zinc oxide (ZnO), silicon (Si), gallium arsenic (GaAs), gallium phosphide (GaP), lithium alumina (LiAl₂O₃), boron nitride (BN), aluminum nitride (AlN), and gallium nitride (GaN) substrate, without being limited thereto. Thegrowth substrate51 may be selected in various ways depending upon materials of semiconductor layers to be formed on thegrowth substrate51. In addition, as shown inFIG. 36, thegrowth substrate51 may have a convex-concave pattern on an upper surface thereof as in a patterned sapphire substrate.
• Thebuffer layer53 is formed to alleviate lattice mismatch between thegrowth substrate51 and thesemiconductor layer55 formed thereon, and may be formed of, for example, gallium nitride (GaN) or aluminum nitride (AlN). When thegrowth substrate51 is a conductive substrate, thebuffer layer53 may be formed of an insulation layer or a semi-insulating layer. For example, thebuffer layer53 may be formed of AlN or semi-insulating GaN.
• Each of thelower semiconductor layer55, theactive layer57 and theupper semiconductor layer59 may be formed of a gallium nitride-based semiconductor material, that is, (Al, In, Ga)N. The lower and upper semiconductor layers55,59 and theactive layer57 may be intermittently or continuously formed by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy, hydride vapor phase epitaxy (HVPE), and the like.
• Here, the upper and lower semiconductor layers may be an n-type semiconductor layer and a p-type semiconductor layer, respectively, or vice versa. Among the gallium nitride-based compound semiconductor layers, an n-type semiconductor layer may be formed by doping an n-type impurity, for example, silicon (Si), and a p-type semiconductor layer may be formed by doping a p-type impurity, for example, magnesium (Mg).
• Referring toFIG. 37, a plurality of light emitting cells S1, S2 spaced apart from each other is formed by a photolithography and etching process. Each of the light emitting cells S1, S2 is formed to have a slanted side surface. Further, in order to partially expose an upper surface of thelower semiconductor layer55 of each of the light emitting cells S1, S2, a photolithography and etching process of partially removing theactive layer57 and theupper semiconductor layer59 is added.
• Referring toFIG. 38, aninsulation layer60bpartially covering the side surface of the first light emitting cell S1 is formed. Theinsulation layer60bmay also extend to cover a region between the first light emitting cell S1 and the second light emitting cell S2 while partially covering a side surface of thelower semiconductor layer55 of the second light emitting cell S2.
• Theinsulation layer60bmay be formed by depositing an insulation material layer, followed by patterning through the photolithography and etching process. Alternatively, theinsulation layer60bmay be formed of an insulation material layer by a lift-off technique. Particularly, theinsulation layer60bmay be formed of a distributed Bragg reflector in which layers having different reflective indexes, for example, SiO₂and TiO₂are alternately stacked. When theinsulation layer60bis formed of a distributed Bragg reflector, which is multiple layers, it is possible to suppress generation of defects such as pinholes in theinsulation layer60b, whereby theinsulation layer60bcan be formed to have a smaller thickness than that of an insulation layer in the related art.
• Then, the transparent electrode layers61,62 are formed on the first and second light emitting cells S1, S2. The transparent electrode layers61,62 may be formed of an indium tin oxide (ITO) layer, a conductive oxide layer such as a zinc oxide layer, or a metal layer such as Ni/Au. The transparent electrode layers61,62 are connected to theupper semiconductor layer59 and are partially disposed on theinsulation layer60b. Further, a portion of the transparent electrode layers61,62, for example, the firsttransparent electrode layer61 may be disposed between the first light emitting cell S1 and the second light emitting cell S2, and on the side surface of thelower semiconductor layer55 of the second light emitting cell S2. The transparent electrode layers61,62 may be formed by a lift-off process, without being limited thereto. Alternatively, the transparent electrode layers61,62 may be formed by a photolithography and etching process.
• Referring toFIG. 10, an insulationprotective layer63 is formed to cover the first and second light emitting cells S1, S2. The insulationprotective layer63 covers the transparent electrode layers61,62 and theinsulation layer60b. In addition, the insulationprotective layer63 may cover an overall area of the first and second light emitting cells S1, S2. The insulationprotective layer63 may be formed of an insulation material layer, such as a silicon oxide or silicon nitride layer, by chemical vapor deposition.
• Referring toFIG. 11, amask pattern70 having an opening is formed on the insulationprotective layer63. The opening of themask pattern70 corresponds to a region for an interconnection line. Then, some region of the insulationprotective layer63 is removed by etching through themask pattern70. As a result, an opening is formed on the insulationprotective layer63 to expose some of the transparent electrode layers61,62 and theinsulation layer60bwhile exposing the exposed region R of thelower semiconductor layer55 of the second light emitting cell S2.
• Referring toFIG. 41, with themask pattern70 remaining on the insulationprotective layer63, a conductive material is deposited to form theinterconnection line65 within the opening of themask pattern70. Here, some of theconductive material65amay be deposited on themask pattern70. The conductive material may be deposited by plating, e-beam evaporation, sputtering, or the like.
• Referring toFIG. 40, themask pattern70, together with some of theconductive material65a, is removed from themask pattern70. As a result, theinterconnection line65 electrically connecting the first and second light emitting cells S1, S2 to each other is completed.
• Here, afirst connection section65pof theinterconnection line65 is connected to thetransparent electrode layer61 of the first light emitting cell S1, and asecond connection section65nthereof is connected to the upper surface of thelower semiconductor layer55 of the second light emitting cell S2, specifically, the exposed region R. Theinterconnection line65 is spaced apart from the side surface of the first light emitting cell S1 by theinsulation layer60b.
• In this exemplary embodiment, thecurrent blocking layer60aand theinsulation layer60bare formed by the same process. As a result, the insulationprotective layer63 and theinterconnection line65 may be formed using thesame mask pattern70, whereby the MJT LED chip can be manufactured by the same number of exposure processes while adding thecurrent blocking layer60a.
• FIG. 42 is a cross-sectional view illustrating an MJT LED chip according to another exemplary embodiment of the present disclosure. The MJT LED chip ofFIG. 42 is similar to the MJT LED chip described with reference toFIG. 35, but has a difference in that it further includes acurrent blocking layer60a.
• Thecurrent blocking layer60amay be disposed on each of the light emitting cells S1, S2, and may be disposed between the transparent electrode layers61,62 and the light emitting cells S1, S2. Specifically, thecurrent blocking layer60amay be disposed between the first light emitting cell S1 and the firsttransparent electrode layer61, thereby spacing a portion of the firsttransparent electrode layer61 from the first light emitting cell S1. Thus, the transparent electrode layers61,62 are partially disposed on thecurrent blocking layer60a. Thecurrent blocking layer60amay be disposed near an edge of each of the light emitting cells S1, S2, but is not limited thereto. Thecurrent blocking layer60amay also be disposed in the center region of each of the light emitting cells S1, S2.
• Since a phenomenon in which the current is concentrated around theinterconnection line65 may be alleviated by thecurrent blocking layer60a, current distribution efficiency of the MJT LED chip may be improved.
• Thecurrent blocking layer60amay be formed of an insulating material, and may particularly include a distributed Bragg reflector in which layers having different reflective indexes are alternately stacked. Theinsulation layer60bmay have the same structure as thecurrent blocking layer60aand may be formed of the same material as thecurrent blocking layer60a, but is not limited thereto. Theinsulation layer60bmay also be formed of a material different from that of thecurrent blocking layer60aby different processes.
• Theinsulation layer60bmay be connected to thecurrent blocking layer60ato be continuously disposed, but the present disclosure is not necessarily limited thereto. Theinsulation layer60band thecurrent blocking layer60amay be disposed to be spaced apart from each other.
• Thecurrent blocking layer60amay be formed by depositing an insulation material layer, followed by patterning through the photolithography and etching process. Alternatively, thecurrent blocking layer60amay be formed of an insulation material layer by a lift-off technique. Particularly, thecurrent blocking layer60amay be formed of a distributed Bragg reflector in which layers having different reflective indexes, for example, SiO₂and TiO₂are alternately stacked. Thecurrent blocking layer60aand theinsulation layer60bmay be connected to each other as shown inFIG. 42, but the present disclosure is not necessarily limited thereto.
• Thecurrent blocking layer60amay be disposed across the entire area in which theinterconnection line65 and the transparent electrode layers61,62 are overlapped with each other. Further, thecurrent blocking layer60aand theinsulation layer60bmay be disposed across the entire area in which theinterconnection line65 and the first light emitting cell S1 are overlapped with each other.
• When thecurrent blocking layer60ahas reflective characteristics like the distributed Bragg reflector, thecurrent blocking layer60amay be disposed substantially in the same region as the region for theinterconnection line65 within a region having an area of two times or less the area of theinterconnection line65. Thecurrent blocking layer60ablocks light emitted from theactive layer57 from being absorbed into theinterconnection line65. However, when occupying an excessively large area, thecurrent blocking layer60acan block emission of light to the outside. Thus, there is a need for restriction of the area thereof.
• Referring toFIG. 42, the transparent electrode layers61,62 are connected to theupper semiconductor layer59 and are partially disposed on thecurrent blocking layer60aand theinsulation layer60b. In addition, thefirst connection section65pof theinterconnection line65 may be connected to the firsttransparent electrode layer61 within an upper region of thecurrent blocking layer60a.
• Structure of Optical Member According to First Embodiment and MJT LED Module Including the Same
• Next, referring toFIG. 3,FIG. 4, andFIG. 19 toFIG. 25, detailed structures and functions of an optical member according to a first embodiment and an MJT LED module including the same will be described.
• Referring toFIG. 3 again, theoptical member130 according to the first embodiment may include alower surface131 and anupper surface135, and may further include aflange137 and legs139. Thelower surface131 includes aconcave section131a, and theupper surface135 includes aconcave surface135aand aconvex surface135b.
• Thelower surface131 is composed of a substantially circular disc-shaped plane, and has theconcave section131aplaced at a central portion thereof. Thelower surface131 is not required to be a flat surface, and may have various convex-concave patterns.
• Further, an inner surface of theconcave section131ahas a surface133 includingside surface133aand anupper end surface133b. Here, theupper end surface133bis perpendicular to a central axis C and theside surface133aextends from theupper end surface133bto an entrance of theconcave section131a. Herein, when aligned to coincide with the optical axis L of theMJT LED100, the central axis C is defined as a central axis of theoptical member130, which becomes a center of a beam distribution of light exiting theoptical member130.
• Theconcave section131amay have a shape, a width of which gradually decreases from the entrance thereof to an upper side thereof. Specifically, theside surface133agradually approaches the central axis C from the entrance of theconcave section131ato theupper end surface133bthereof. With this structure, a region for theupper end surface133bmay be formed narrower than the entrance of theconcave section131a. Theside surface133amay have a relatively gentle slope near theupper end surface133b.
• The region for theupper end surface133bis defined within a narrower region than a region for the entrance of theconcave section131a. In addition, the region for theupper end surface133bmay be defined within a narrower region than a region surrounded by an inflection curve at which theconcave surface135aof theupper surface135 meets theconvex surface135bthereof. Further, the region for theupper end surface133bmay be placed within a narrower region than a region for thecavity121a(FIG. 4) of the MJT LED, that is, a light exit region.
• The region for theupper end surface133breduces variation of the beam distribution of light exiting theoptical member130 through theupper surface135 thereof even in the case of misalignment between the optical axis L of the MJT LED and the central axis C of theoptical member130. Thus, the region for theupper end surface133bmay be minimized in consideration of misalignment between theMJT LED100 and theoptical member130.
• Further, theupper surface135 of theoptical member130 includes theconcave surface135aand theconvex surface135bcontinuously extending from theconcave surface135awith reference to the central axis C. A line at which theconcave surface135ameets theconvex surface135bbecomes the inflection curve. Theconcave surface135adisperses light exiting near the central axis C of theoptical member130 through refraction of the light at a relatively large angle. Further, theconvex surface135bincreases the quantity of light exiting towards an outer direction of the central axis C.
• Theupper surface135 and theconcave section131ahave a symmetrical structure relative to the central axis C. For example, theupper surface135 and theconcave section131ahave a mirror symmetry structure relative to a plane passing through the central axis C and may have a rotational body shape relative to the central axis C. In addition, theconcave section131aand theupper surface135 may have various shapes according to a desired light beam distribution.
• In another aspect, theflange137 connects theupper surface135 to thelower surface131 and defines an outer size of the optical member. A side surface of theflange137 and thelower surface131 may be formed with convex-concave patterns. The legs139 of theoptical member130 are coupled to the printedcircuit board110 to support thelower surface131 while separating thelower surface131 from the printedcircuit board110. Coupling of the legs139 to the printedcircuit board110 may be performed by bonding a distal end of each of the legs139 to the printedcircuit board110 using an adhesive or by fitting each of the legs139 into a corresponding hole formed in the printedcircuit board110.
• Theoptical member130 is separated from theMJT LED100, so that an air gap is formed in theconcave section131a. Thehousing121 of theMJT LED100 is placed below thelower surface131, and thewavelength conversion layer125 of theMJT LED100 is separated from theconcave section131ato be placed under thelower surface131. With this structure, light traveling in theconcave section131ais prevented from being lost due to absorption by thehousing121 or thewavelength conversion layer125.
• According to this embodiment, when a perpendicular plane relative to the central axis C is formed within theconcave section131a, it is possible to reduce variation of the beam distribution of light exiting theoptical member130 even upon misalignment between theMJT LED100 and theoptical member130. Furthermore, since theconcave section131adoes not have a relatively sharp apex, the optical member can be easily manufactured.
• FIG. 19 shows sectional views of various modifications of the optical member. Herein, various modifications of theconcave section131ashown inFIG. 3 will be described.
• InFIG. 19A, theupper end surface133bperpendicular to the central axis C described inFIG. 3 has a downwardly protruding surface formed at a portion thereof near the central axis C. With this downwardly protruding surface, the optical member can achieve primary control of light entering the portion of the optical member near the central axis C thereof.
• The upper end surface ofFIG. 19B is similar to that ofFIG. 19A except that the upper end surface ofFIG. 19B has upwardly protruding surfaces formed at portions thereof perpendicular to the central axis C of the optical member. Since the upper end surface is combined with the upwardly protruding surfaces and the downwardly protruding surface, the optical member can reduce variation in light beam distribution due to misalignment between the MJT LED and the optical member.
• The upper end surface ofFIG. 19C is different from that ofFIG. 3 in that theupper end surface133bis formed with an upwardly protruding surface at a portion thereof near the central axis C of the optical member. With this upwardly protruding surface, the optical member can achieve further dispersion of light entering the portion of the optical member near the central axis C thereof.
• The upper end surface ofFIG. 19D is similar to that ofFIG. 19C except that the upper end surface has downwardly protruding surfaces at portions thereof perpendicular to the central axis C of the optical member. Since the upper end surface is combined with the upwardly protruding surfaces and the downwardly protruding surface, the optical member can reduce variation in light beam distribution due to misalignment between the MJT LED and the optical member.
• FIG. 20 shows sectional views of an optical member, illustrating an MJT LED module according to a further exemplary embodiment of the present disclosure.
• Referring toFIG. 20A, theupper end surface133bmay be formed with alight scattering pattern133c. Thelight scattering pattern133cmay be a convex-concave pattern. In addition, theconcave surface135amay also be formed with alight scattering pattern135c. Thelight scattering pattern135cmay also be a convex-concave pattern.
• Generally, a relatively large luminous flux is concentrated near the central axis C of the optical member. Furthermore, according to embodiments of the present disclosure, since theupper end surface133bis perpendicular to the central axis C, more luminous flux can be concentrated near the central axis C. Accordingly, with the structure of theupper end surface133band/or theconcave surface135ahaving thelight scattering patterns133c,135c, it is possible to disperse luminous flux near the central axis C of the optical member.
• Referring toFIG. 20B, amaterial layer139ahaving a different index of refraction than that of theoptical member130 may be placed on theupper end surface133b. The index of refraction of thematerial layer139amay be higher than that of the optical member, thereby allowing change of an optical path of light incident on theupper end surface133b.
• Further, amaterial layer139bhaving a different index of refraction than that of theoptical member130 may also be placed on theconcave surface135a. The index of refraction of thematerial layer139bmay be higher than that of the optical member, thereby allowing change of an optical path of light exiting through theconcave surface135a.
• Thelight scattering patterns133c,135cofFIG. 20A and the material layers139a,139bofFIG. 20B may also be applied to the various optical members ofFIG. 19.
• FIG. 21 is a sectional view illustrating dimensions of an MJT LED module used for simulation. Here, the same reference numerals as those ofFIGS. 3 and 4 are used (please also refer toFIGS. 3 and 4 for a depiction of some elements).
• In theMJT LED100, thecavity121ahas a diameter of 2.1 mm and a height of 0.6 mm. Thewavelength conversion layer125 fills thecavity121aand has a flat surface. A distance (d) between theMJT LED100 and thelower surface131 of theoptical member130 is 0.18 mm and theMJT LED100 and theoptical member130 are arranged such that the optical axis L of theMJT LED100 is aligned with the central axis C of the optical member.
• Theoptical member130 has a height (H) of 4.7 mm and an upper surface of the optical member has a width (W1) of 15 mm. Theconcave surface135ahas a width (W2) of 4.3 mm. Further, the entrance of theconcave section131aplaced on thelower surface131 has a width (w1) of 2.3 mm, and theupper end surface133bhas a width (w2) of 0.5 mm. Theconcave section131ahas a height (h) of 1.8 mm.
• FIGS. 22A, 22B, and 22C show graphs depicting a shape of the optical member ofFIG. 21. Here,FIG. 22A is a sectional view of the optical member illustrating reference point P, distance R, angle of incidence θ1, and exit angle θ5;FIG. 22B shows variation of distance R according to angle of incidence θ1; andFIG. 22C shows variation of θ5/θ1 according to angle of incidence θ1.FIG. 23 shows traveling directions of light beams entering theoptical member130 from reference point P at intervals of 3°.
• Referring toFIG. 22A, reference point P indicates a light exit point of theMJT LED100 placed on the optical axis L. Properly, reference point P is set to be placed on an outer surface of thewavelength conversion layer125 in order to exclude external factors, such as light scattering by the phosphors in theMJT LED100 and the like.
• θ1 indicates an angle of incidence of light entering theoptical member130 from the reference point P, and θ5 indicates an exit angle of light exiting theoptical member130 through theupper surface135 thereof. R indicates a distance from reference point P to the inner surface of theconcave section131a.
• Referring toFIG. 22B, since theupper end surface133bof theconcave section131ais perpendicular to the central axis C, R slightly increases with increasing θ1. An enlarged graph inFIG. 22B shows an increasing curve of R. On theside surface133aof theconcave section131a, R decreases with increasing θ1 and slightly increases near the entrance of theconcave section131a.
• Referring toFIG. 22C, as θ1 increases, θ5/θ1 rapidly increases near theconcave surface135aand relatively gently decreases near theconvex surface135b. In this embodiment, as shown inFIG. 23, luminous flux exiting the optical member through theconcave surface135athereof may overlap luminous flux exiting the optical member through theconvex surface135bthereof. That is, among light beams entering the optical member from reference point P, light exiting the optical member through theconcave surface135anear the inflection curve may have a higher refraction angle than light exiting the optical member through theconvex surface135b. Thus, it is possible to reduce concentration of luminous flux near the central axis C by forming theupper end surface133bof theconcave section131ato have a planar shape and adjusting the shapes of theconcave surface135aand theconvex surface135b.
• FIGS. 24A and 24B shows graphs depicting illuminance distribution. Specifically,FIG. 24A is a graph depicting illuminance distribution of an MJT LED, andFIG. 24B is a graph showing illuminance distribution of the MJT LED module using an optical member. Illuminance distribution is represented as a magnitude of luminous flux density of light entering a screen separated a distance of 25 mm from a reference point.
• As shown inFIG. 24A, theMJT LED100 provides a bilaterally symmetric illumination distribution with reference to the optical axis (C), and has a luminous flux density which is very high at the center thereof and rapidly decreases towards the periphery thereof. When theoptical member130 is applied to theMJT LED100, the MJT LED100 can provide a substantially uniform luminous flux density within a radius of 40 mm, as shown inFIG. 24B.
• FIGS. 25A and 25B show graphs depicting light beam distributions. Specifically,FIG. 25A is a graph depicting a light beam distribution of an MJT LED, andFIG. 25B is a graph depicting a light beam distribution of the MJT LED module using an optical member. The light beam distribution shows light intensity at a place separated a distance of 5 m from reference point P according to a beam angle, and beam distributions in orthogonal directions are shown to overlap each other in one graph.
• As shown inFIG. 25A, the intensity of light emitted from theMJT LED100 is high at a beam angle of 0°, that is, at the center thereof, and gradually decreases with increasing beam angle. When the optical member is applied to theMJT LED100, the intensity of light emitted from theMJT LED100 is relatively low at a beam angle of 0° and is relatively high near a beam angle of 70°, as shown inFIG. 25B.
• Accordingly, when theoptical member130 is applied to theMJT LED100, it is possible to achieve uniform backlighting of a relatively wide area through change of the light beam distribution of the MJT LED, which has high light intensity at the center thereof.
• Structure of Optical Member According to Second Embodiment and MJT LED Module Including the Same
• Next, referring toFIG. 26 toFIG. 33B, detailed structures and functions of an optical member according to a second embodiment and an MJT LED module including the same will be described.
• FIG. 26 is a sectional view of an MJT LED module according to one exemplary embodiment of the present disclosure, andFIG. 27A,FIG. 27B andFIG. 27C are sectional views of the MJT LED module taken along lines a-a, b-b and c-c ofFIG. 26. Here, line a-a corresponds to a line on a lower surface of the optical member, line c-c corresponds to a line on an upper surface of the optical member, and line b-b corresponds to a cutting line at the middle of the height of a diffusion lens between line a-a and line c-c. Further,FIG. 28 is a detailed view of an optical member of the MJT LED module shown inFIG. 26, andFIG. 29 shows a light beam angle distribution of the MJT LED module using the optical member ofFIG. 28.
• Referring toFIG. 26, the MJT LED module includes anMJT LED100 and anoptical member230 disposed on theMJT LED100 and formed of a resin or glass material. Although the printedcircuit board110 is partially shown to show a single MJT LED module in this embodiment, a plurality of MJT LED modules is regularly arranged on a single printedcircuit board110 to form thebacklight module300 as described above.
• First, theMJT LED100 and the printedcircuit board110 are the same as those of the first embodiment described above with reference toFIG. 3 andFIG. 4, and detailed descriptions thereof will be omitted. Thus, theoptical member230 according to the second embodiment will be mainly described hereinafter.
• Referring toFIG. 26, theoptical member230 includes alower surface231 and alight exit face235 at the opposite side thereof, and may further includelegs239. Thelower surface231 includes a concavelight incident section231a. Thelight exit face235 is generally composed of an upwardly protruding round surface, and includes aflat surface235aformed at an upper center thereof. Theflat surface235ais placed corresponding to a concave section of an optical member such as aspects of the optical member shown in the first embodiment, and theoptical member230 according to the present embodiment can disperse light near the optical axis by the structure of alight incident section231adescribed in detail hereinafter even without the concave section at the upper center of the light exit face. Thelight incident section231ahas a substantially bell-shaped cross-section. That is, thelight incident section231ahas a shape which gradually converges from a lower entrance thereof adjacent theMJT LED100 towards an upper apex thereof.
• Referring toFIG. 27A, thelower surface231 of theoptical member230 has a circular shape. In addition, thelight incident section231ahas a lower portion placed at a center of thelower surface231, and the lower portion of thelight incident section231ahas a circular shape. Thelight incident section231amaintains a circular shape from the lower entrance immediately before the upper apex thereof, and has a gradually decreasing diameter in an upward direction. Referring toFIG. 27C, the upperflat surface235aof theoptical member230 also has a circular shape.
• Referring toFIG. 27A,FIG. 27B andFIG. 27C in order, theoptical member230 includes thelower surface231 having a circular shape, and has a gradually decreasing diameter in the upward direction. Theoptical member230 may have a greater variation in diameter of a circular outer circumference at an upper portion of a side surface thereof than that of the circular outer circumference at a lower portion of the side surface thereof. The circular shape of thelight incident section231ahas a gradually decreasing diameter.
• Referring toFIG. 28, an optical axis L corresponding to the central axis of theoptical member230 is shown. To obtain a uniform light distribution using theoptical member230, it is necessary to have a light intensity peak at an angle of 60° or more from the optical axis L. To obtain such optical characteristics, it is important to achieve effective dispersion of light at an angle of 50° or less from the optical axis L.FIG. 28 shows reference line (r) at an angle of 50° or less relative to the optical axis L.
• To achieve effective dispersion of light at an angle of 50° or less from the optical axis L, within the range between the optical axis L and the reference line (r), that is, at an angle of 50° or less from the optical axis L, the shortest distance ‘b’ from a certain point (p) on the optical axis L to the apex of thelight incident section231ais greater than the shortest distance ‘a’ from the point (p) to the side surface of thelight incident section231a. As above, when b>a, thelight incident section231acan contribute to wide dispersion of light traveling within an angle of 50° or less from the optical axis L to an angle of 60° or more from the optical axis L. In contrast, when b<a, thelight incident section231afails to contribution to wide dispersion of light traveling within an angle of 50° or less from the optical axis L. As such, it is necessary to form a separate concave section for wide dispersion of light at the upper center of the light exit face in the related art. In other words, theoptical member230 according to the present disclosure employs the curved structure of thelight incident section231asatisfying the condition of b>a within an angle of 50° or less from the optical axis L and thus the concave section at the upper center of the light exit face can be omitted.
• Here, thelight incident section231apreferably has a height greater than a radius R of the lower entrance of thelight incident section231a. More preferably, the height H of thelight incident section231ais 1.5 times or more the radius R thereof. In addition, a lower portion of thelight incident section231aadjoins air which has a lower index of refraction than the resin or glass material, and an upper portion of the light exit face also adjoins air which has a lower index of refraction than the resin or glass material.
• FIG. 29 shows a light beam angle distribution of the MJT LED module using the optical member ofFIG. 28. Referring toFIG. 29, it can be seen that a light intensity peak is formed at about 72° from the optical axis L and light is widely distributed. From the result ofFIG. 29, it can be seen that theoptical member230 according to the present disclosure can uniformly disperse light at an angle of 60° or less from the optical axis L through the curved structure of thelight incident section231asatisfying the condition of b>a at an angle of 50° or less from the optical axis L even without the concave section at the upper center of the light exit face, thereby achieving uniform distribution of light.
• FIG. 30 is a sectional view of an optical member according to another exemplary embodiment of the present disclosure. As clearly shown inFIG. 30, theoptical member230 according to this embodiment has the same curved structure of thelight incident section231aas that of the optical member shown inFIG. 28. Thus, thelight incident section231aof the optical member according to this embodiment satisfies the condition of b>a at an angle of 50° or less from the optical axis L. Here, unlike the optical member according to the above embodiment, which has the flat surface formed at the upper center of the light exit face, theoptical member230 according to this embodiment has a convexlyround surface235bat the upper center of the light exit face.
• FIG. 31 clearly shows a beam angle distribution curve of an MJT LED module using the optical member ofFIG. 30. Referring toFIG. 31, it can be seen that a light intensity peak is formed at about 72° from the optical axis L and light is widely distributed. In addition, there is no significant difference between the light beam angle distribution ofFIG. 31 and the light beam angle distribution ofFIG. 29. Thus, it can be seen that, when thelight incident section231asatisfies the condition of b>a at an angle of 50° or less from the optical axis L, there is no significant difference in light beam angle distribution, regardless of whether the light exit face has the flat surface or the convex surface at the upper center thereof.
• FIGS. 32A and 32B show an optical member according to Comparative Example 1 and a beam angle distribution curve thereof.
• In the optical member ofFIG. 32A, at an angle of 50° or less from the optical axis L, the shortest distance ‘b’ from a certain point on the optical axis to an apex of a light incident section is greater than the shortest distance ‘a’ from the same point to a side surface of the light incident section, and the light exit face has a concave section formed at an upper center thereof. InFIG. 32B showing a beam angle distribution curve under these conditions, it can be seen that there is no substantial difference in light beam angle distribution between the above embodiments and this comparative example. This result means that, under the condition of b>a, the concave section formed at the upper center of the light exit face provides substantially no function in change of the light beam angle distribution.
• FIGS. 33A and B show an optical member according to Comparative Example 2 and a light beam angle distribution thereof.
• In the optical member ofFIG. 33A, at an angle of 50° or less from the optical axis L, the shortest distance ‘b’ from a certain point on the optical axis to an apex of a light incident section is smaller than the shortest distance ‘a’ from the same point to a side surface of the light incident section, and the light exit face has a concave section formed at an upper center thereof. InFIG. 33B showing a beam angle distribution curve under these conditions, it can be seen that there is no substantial difference between the light beam angle distribution of Comparative Example 1 and that of the above embodiments. This result means that, under the condition of b<a, the concave section formed at the upper center of the light exit face contributes to wide dispersion of light at an angle of 50° or less from the optical axis L.
• Although the present disclosure has been illustrated with reference to some exemplary embodiments in conjunction with the drawings, it should be understood that some features of a certain embodiment may also be applied to other embodiments without departing from the spirit and scope of the disclosure. Further, it should be understood that these embodiments are provided by way of illustration only, and that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.
• FIG. 43A andFIG. 43B are schematic views comparing a backlight unit (FIG. 43A) in the related art with a backlight unit (FIG. 43B) according to one exemplary embodiment of the present disclosure.
• Referring toFIG. 43A, the backlight unit in the related art includes a plurality of LED chips having a single light emitting cell, and the plurality of LED chips are connected to each other in series and/or in parallel to form one ormore arrays110a, thereby enabling an operation in a unit of eacharray110a. On the other hand, in the backlight unit illustrated inFIG. 43B according to one exemplary embodiment of the present disclosure, MJT LEDs may be independently operated without being connected to each other in series, in parallel, or in series/parallel. As a result, for example, the backlight unit in the related art may have 9arrays110a, while the backlight unit according to the present disclosure may include 45 blocks.
• Depending on the configuration difference as described above, the following effect difference exhibits. It is assumed that the backlight unit in the related art ofFIG. 43A is Comparative example, and the backlight unit according to the present disclosure ofFIG. 43B is one of Inventive examples. All of the backlight units of Comparative example and the Inventive example have been operated at a DC converter voltage of 24V, and an IC operating voltage was 3V. An operating voltage of an LED chip of a single light emitting cell of Comparative example was 3.6V, and a loss voltage of each array was 3V. In addition, an operating voltage of one MJT LED of the Inventive example was 3.3V, and a loss voltage of eachblock110bwas 1.2V.
• The backlight unit of Comparative example may be operated at 0.4 A, and the backlight unit of the Inventive example may be operated at 0.075 A. As a result, the droop phenomenon occurring at high current may be reduced. In addition, since operation power of Comparative example is 75.6 W, and operating power of the Inventive example is 70.87 W, loss power of Comparative example was 10.8 W and loss power of Inventive example was 4.05 W, and operating efficiency calculated based on those described above was 85.7% (Comparative example) and 94.2% (Inventive example), respectively. Thus, it may be confirmed that the operating efficiency of the backlight unit according to the present disclosure is higher than that of the related art.
• According to one or more exemplary embodiments of the present disclosure, the backlight module is fabricated using the MJT LEDs having low current operation characteristics, thereby enabling low current operation of the backlight module and the backlight unit including the same.
• In addition, according to one or more exemplary embodiments of the present disclosure, one connection section of the interconnection line electrically contacts a slanted side surface of the light emitting cell, thereby increasing an effective light emitting area of each of light emitting cells in an MJT LED chip.
• Further, according to one or more exemplary embodiments of the present disclosure, it is possible to enhance stability and reliability of drive circuits for controlling operation of the backlight module while reducing manufacturing costs.
• Further, according to one or more exemplary embodiments of the present disclosure, the backlight unit has improved power efficiency and luminous efficacy, and can prevent a droop phenomenon due to operation at high current.
• Further, according to one or more exemplary embodiments of the present disclosure, it is possible to minimize or reduce the number of LEDs constituting the backlight module and to allow an individual operation of the MJT LEDs constituting the backlight module.

Claims (18)

What is claimed is:

1. A backlight unit, comprising

a backlight module, comprising:

a printed circuit board comprising blocks; and

light emitting diode (LED) chips disposed on the blocks; and

a backlight control module configured to perform a dimming control of the LED chips,

wherein each of the LED chips comprises:

light emitting cells spaced apart from each other, each of the light emitting cells comprising a lower semiconductor layer, an upper semiconductor layer disposed on the lower semiconductor layer, and an active layer disposed between the lower and upper semiconductor layers, the lower semiconductor layers of the light emitting cells being partially exposed;

connection structures electrically connecting the light emitting cells to each other, each of the connection structures electrically connecting an upper semiconductor layer of one light emitting cell to a lower semiconductor layer of another light emitting cell; and

an insulation layer disposed between the light emitting cells and the connection structures, the insulation layer covering a portion of the exposed lower semiconductor layers and having a width wider than the connection structures.

2. The backlight unit ofclaim 1, wherein:

each of the light emitting cells comprises first to N^thlight emitting cells, N is a natural number of 2 or greater; and

a connection structure for electrical connection between the N^thlight emitting cell and an N-1^thlight emitting cell is the same as that between the first light emitting cell and a second light emitting cell.

3. The backlight unit ofclaim 2, wherein each of the LED chips further comprises a single substrate on which the light emitting cells are disposed.

4. The backlight unit ofclaim 3, wherein:

a surface of the single substrate is exposed between two light emitting cells; and

the insulation layer covers the exposed surface of the single substrate.

5. The backlight unit ofclaim 4, wherein each of the connection structure comprises an interconnection line.

6. The backlight unit ofclaim 1, wherein each of the LED chips further comprises:

transparent electrode layers disposed on the light emitting cells and contacting the upper semiconductor layers; and

an insulation protective layers covering the transparent electrode layers, the insulation protective layers having openings exposing the transparent electrode layers.

7. The backlight unit ofclaim 2, wherein:

the lower semiconductor layer of an M^thlight emitting cell is electrically connected to the upper semiconductor layer of an M-1^thlight emitting cell; and

M is a natural number of 2 or greater, and less than or equal to N.

8. The backlight unit ofclaim 1, wherein the backlight control module comprises:

an operation power generator configured to provide an operating voltage to the LED chips; and

an operation controller configured to independently control a dimming level of each of the blocks.

9. The backlight unit ofclaim 8, wherein:

each of the blocks comprises an anode terminal and a cathode terminal; and

the anode terminal of each of the blocks is directly connected to the operation power generator and the cathode terminal of each of the blocks is directly connected to the operation controller.

10. The backlight unit ofclaim 9, wherein:

an operating voltage of each of the blocks is in a range of about to 6V to about to 36V; and

an operating current of each of the blocks is equal to or less than 125 mA.

11. The backlight unit ofclaim 1, further comprising optical members disposed on the LED chips, each of the optical members being configured to change a light beam distribution of a corresponding LED chip.

12. The backlight unit ofclaim 11, wherein each of the optical members is disposed directly on each of the LED chips.

13. A display device, comprising:

a liquid crystal panel; and

a direct type backlight unit disposed under the liquid crystal panel, the direct type backlight unit comprising:

a backlight module, comprising:

a printed circuit board comprising blocks; and

light emitting diode (LED) chips disposed on the blocks; and

a backlight control module configured to perform a dimming control of the LED chips,

wherein each of the LED chips comprises:

light emitting cells spaced apart from each other, each of the light emitting cells comprising a lower semiconductor layer, an upper semiconductor layer disposed on the lower semiconductor layer, and an active layer disposed between the lower and upper semiconductor layers, the lower semiconductor layers being partially exposed;

connection structures electrically connecting the light emitting cells to each other, each of the connection structures electrically connecting an upper semiconductor layer of one light emitting cell to a lower semiconductor layer of another light emitting cell; and

an insulation layer disposed between the light emitting cells and the connection structures, the insulation layer covering a portion of the exposed lower semiconductor layers and having a width wider than the connection structures.

14. The display device ofclaim 13, wherein:

each of the light emitting cells comprises first to N^thlight emitting cells, N is a natural number of 2 or greater; and

a connection structure for electrical connection between the N^thlight emitting cell and an N-1^thlight emitting cell is the same as that between the first light emitting cell and a second light emitting cell.

15. The display device ofclaim 14, wherein each of the LED chips further comprises a single substrate on which the light emitting cells are disposed.

16. The display device ofclaim 13, wherein the backlight control module comprises:

an operation power generator configured to provide an operating voltage to the LED chips; and

an operation controller configured to independently control a dimming level of each of the blocks.

17. The display device ofclaim 16, wherein:

each of the blocks comprises an anode terminal and a cathode terminal; and

the anode terminal of each of the blocks is directly connected to the operation power generator and the cathode terminal of each of the blocks is directly connected to the operation controller.

18. The display device ofclaim 13, wherein each of the LED chips further comprises:

transparent electrode layers disposed on the light emitting cells and contacting the upper semiconductor layers; and

an insulation protective layers covering the transparent electrode layers, the insulation protective layers having openings exposing the transparent electrode layers.

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