USRE47804E1 - Luminescent display device - Google Patents

Abstract

A luminescent display device includes a substrate and a thin-film transistor above the substrate. The thin-film transistor includes a semiconductor layer, a gate insulating film on the semiconductor layer, a gate electrode on the gate insulating film, a source electrode, and a drain electrode. The luminescent display device further includes an interlayer insulating film on the gate electrode, a first capacitor electrode on the interlayer insulating film in a region above the gate electrode, and a luminescent element configured to be driven by a driver to produce luminescence. The driver includes the thin-film transistor, and the first capacitor electrode and the gate electrode constitute a capacitor.

Description

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation application of PCT Application No. PCT/JP2009/006415, filed on Nov. 27, 2009, designating the United States of America, the disclosure of which, including the specification, drawings, and claims, is incorporated herein by reference in its entirety.NOTICE: More than one reissue application has been filed for the reissue of U.S. Pat. No. 9,461,102 B2. Reissue Application Ser. No. 16/145,623 is a reissue of U.S. Pat. No. 9,461,102 B2 and was filed on Sep. 28, 2018. Reissue Appl. Ser. No. 16/671,675 is a reissue of U.S. Pat. No. 9,461,102 B2, was filed on Nov. 1, 2019, and is a continuation reissue application of Reissue application Ser. No. 16/145,623.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to luminescent display devices, and particularly to an active-matrix luminescent display device which includes a luminescent element and a driving circuit having a capacitor and a thin-film transistor.

2. Description of the Related Art

Conventionally, there is an active development of luminescent display devices, such as organic electroluminescent elements (hereinafter abbreviated as organic EL elements), in which luminescent elements that control the luminance using an electric current are two-dimensionally arranged. In particular, there is an ongoing development of active-matrix luminescent display devices in which pixel circuits are arranged which include, for each luminescent element, a driving circuit for driving the luminescent element.

The driving circuit generally includes: a switching transistor which selects a pixel for producing luminescence; a driving transistor which drives a luminescent element; and a capacitor. The driving circuit includes, for example, a capacitor which holds a voltage for determining an amount of a current passed by the driving transistor (see Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2006-330736).

FIG. 1 shows the layout of aluminescent pixel700 included in a conventional luminescent display device disclosed inPatent Literature 1. As shown inFIG. 1, theluminescent pixel700 is wired with asignal line705, ascanning line706, and apower line707. Further, theluminescent pixel700 includes aswitching transistor701, acapacitor702, adriving transistor703, and aluminescent element704. Theluminescent element704 is formed in the luminescent region of theluminescent pixel700, whereas theswitching transistor701, thecapacitor702, and thedriving transistor703 are formed in the driving circuit region.

SUMMARY OF THE INVENTION

With the above conventional technique, however, a region dedicated to the capacitor is formed, thereby causing a problem that when the number of capacitors or the capacitor area increases, the region for forming other elements becomes smaller, resulting in less design flexibility.

For example, as in the luminescent display device ofPatent Literature 1 shown inFIG. 1, most of the driving circuit region is occupied by thecapacitor702. Therefore, in the case of forming acapacitor702 which occupies a larger area or in the case of forming another capacitor, the region for forming the drivingtransistor703 and theswitching transistor701 becomes smaller. Alternatively, the luminescent region becomes smaller, leading to an increase in the density of the current flowing in the luminescent element, thereby reducing the lifetime of the luminescent element.

In view of the above, the present invention has been conceived to solve the above conventional problem, and it is an object of the present invention to provide a luminescent display device with higher design flexibility by forming a capacitor without a region dedicated to the capacitor or a new region dedicated to the capacitor.

In order to achieve the above object, the luminescent display device according to an aspect of the present invention is a luminescent display device including: a substrate; a thin-film transistor which is formed above the substrate and includes: a semiconductor layer having a channel region, a source region, and a drain region; a gate insulating film formed on the semiconductor layer; a gate electrode formed on the gate insulating film; and a source electrode and a drain electrode which are electrically connected to the source region and the drain region of the semiconductor layer, respectively; an interlayer insulating film formed on the gate electrode; a luminescent element which is driven by a driving circuit to produce luminescence, the driving circuit including the thin-film transistor; and a first capacitor electrode formed on the interlayer insulating film in a region above the gate electrode, wherein the first capacitor electrode and the gate electrode constitute a first capacitor.

According to the present invention, it is possible to provide a luminescent display device with higher design flexibility by forming a capacitor without a region dedicated to the capacitor or a new region dedicated to the capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the Drawings:

FIG. 1 shows the layout of a pixel included in a conventional luminescent display device;

FIG. 2 is a block diagram showing an example structure of a luminescent display device according toEmbodiment 1;

FIG. 3 shows a circuit structure of a luminescent pixel included in a display unit according toEmbodiment 1;

FIG. 4 shows an example layout of a luminescent pixel according toEmbodiment 1;

FIG. 5 shows a cross-sectional view of a luminescent pixel according toEmbodiment 1;

FIG. 6 shows a circuit structure of a luminescent pixel according to a variation ofEmbodiment 1;

FIG. 7 shows a cross-sectional view of a luminescent pixel according to a variation ofEmbodiment 1;

FIG. 8 shows a circuit structure of a luminescent pixel according to another variation ofEmbodiment 1;

FIG. 9 shows a cross-sectional view of a luminescent pixel according to another variation ofEmbodiment 1;

FIG. 10 shows a circuit structure of a luminescent pixel included in a display unit according to Embodiment 2;

FIG. 11 shows an example layout of a luminescent pixel according to Embodiment 2;

FIG. 12 shows a cross-sectional view of a luminescent pixel according to Embodiment 2;

FIG. 13 is an external view of a television set which includes a luminescent display device according to the present invention; and

FIG. 14 shows an example layout of a luminescent pixel in another variation of a luminescent display device according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Hereinafter, embodiments of the luminescent display device according to the present invention are described with reference to the drawings.

The luminescent display device according to an aspect of the present invention is a luminescent display device including: a substrate; a thin-film transistor which is formed above the substrate and includes: a semiconductor layer having a channel region, a source region, and a drain region; a gate insulating film formed on the semiconductor layer; a gate electrode formed on the gate insulating film; and a source electrode and a drain electrode which are electrically connected to the source region and the drain region of the semiconductor layer, respectively; an interlayer insulating film formed on the gate electrode; a luminescent element which is driven by a driving circuit to produce luminescence, the driving circuit including the thin-film transistor; and a first capacitor electrode formed on the interlayer insulating film in a region above the gate electrode, wherein the first capacitor electrode and the gate electrode constitute a first capacitor.

With this, the gate electrode of the thin-film transistor is used not only simply as the gate electrode but also as one of two electrodes constituting the capacitor. Thus, the capacitor can be formed above the thin-film transistor to overlap with the thin-film transistor, enabling efficient use of the pixel space. As a result, a complex driving circuit which includes multiple thin-film transistors and multiple capacitors can be formed in a region having a limited area. It is to be noted that the structure of the present invention can be applied to a capacitor for holding the gate voltage, as well as a capacitor for holding a threshold voltage Vth in the driving circuit.

Further, the luminescent display device may include a plurality of first capacitor electrodes including the first capacitor electrode, wherein each of the plurality of first capacitor electrodes and the gate electrode may constitute the first capacitor.

Furthermore, the first capacitor electrode and one of the source electrode and the drain electrode may form one layer, and the one of the source electrode and the drain electrode may be electrically connected to the first capacitor electrode.

With this, the other one of the two electrodes constituting the capacitor and one of the source electrode and the drain electrode can be formed in one process.

Moreover, the luminescent element may be electrically connected to one of the source electrode and the drain electrode, the thin-film transistor may be a driving transistor which supplies a driving current to the luminescent element, and the first capacitor may be a capacitor for setting a value of a current flowing in the driving transistor.

This makes it possible to form, in the driving circuit, the capacitor for setting the value of the driving current flowing in the driving transistor, while efficiently using the pixel space.

Further, the thin-film transistor may be a switching transistor which determines timing of supplying a driving current to the luminescent element, and the first capacitor may be a capacitor for initializing a capacitor used for setting a value of the driving current.

With this, one of the capacitor electrodes of the capacitor can be used also as, not only the gate electrode of the driving transistor, but also the gate electrode of the switching transistor. Therefore, it is possible to arrange a greater number of thin-film transistors and capacitors by efficiently using the limited pixel space.

Furthermore, the luminescent display device may further include a second capacitor, wherein the second capacitor may be electrically connected to the first capacitor in parallel.

With this, in addition to the first capacitor, the second capacitor is also formed in parallel, making it possible to increase the capacitance by the capacitance of the second capacitor.

Further, the second capacitor may include an upper second capacitor electrode and a lower second capacitor electrode, one of the upper second capacitor electrode and the lower second capacitor electrode may be electrically connected to the gate electrode, and the other one of the upper second capacitor electrode and the lower second capacitor electrode may be electrically connected to one of the source electrode and the drain electrode.

This makes it possible to increase the capacitance by the capacitance of the second capacitor, allowing for stability in the voltage even when there is a leak current, and thus crosstalk can be reduced.

Furthermore, the upper second capacitor electrode and one of the source electrode and the drain electrode may form one layer, the lower second capacitor electrode and the gate electrode may form one layer, and the first capacitor electrode may be electrically connected to the upper second capacitor electrode and to one of the source electrode and the drain electrode.

This makes it possible to form, as one layer, first ones of the capacitor electrodes constituting the first capacitor and the second capacitor, and to form, as another layer, second ones of the capacitor electrodes constituting the first capacitor and the second capacitor, thereby enabling reduction in the number of manufacturing processes.

Moreover, an area of a lower surface of the first capacitor electrode, which is part of the first capacitor, in the region above the gate electrode may be 30% to 100% of an area of an upper surface of the gate electrode.

Further, the semiconductor layer may be made of polysilicon.

Furthermore, the luminescent element may be an organic electroluminescent element.

Furthermore, a capacitance of the first capacitor may be 0.1 to 10 pF.

Moreover, the luminescent display device may be a top-emission luminescent display device, and the luminescent element may be formed in a layer above the first capacitor electrode.

Moreover, the luminescent display device may be a bottom-emission luminescent display device, and the thin-film transistor and the first capacitor may be formed in a region other than a luminescent region in which the luminescent element is formed.

Embodiment 1

The luminescent display device according toEmbodiment 1 includes a driving transistor and a capacitor, and the gate electrode of the driving transistor is one of two capacitor electrodes constituting the capacitor. Thus, the capacitor is formed in a region which is above the driving transistor and which includes the gate electrode of the driving transistor.

FIG. 2 is a block diagram showing an electrical structure of aluminescent display device10 according toEmbodiment 1. Theluminescent display device10 inFIG. 2 at least includes acontrol circuit20, a scanningline driving circuit40, a signalline driving circuit50, and adisplay unit60.

FIG. 3 shows a circuit structure of aluminescent pixel100 included in thedisplay unit60 according toEmbodiment 1. Theluminescent pixel100 inFIG. 3 includes a switchingtransistor101, acapacitor102, a drivingtransistor103, anorganic EL element104, asignal line105, ascanning line106, a higher-voltage-side power line107, and a lower-voltage-side power line108.

First, the following describes the connection relationships and functions of the structural elements shown inFIG. 2.

Thecontrol circuit20 has a function to control the scanningline driving circuit40 and the signalline driving circuit50. Thecontrol circuit20 outputs a video signal received from outside, to the signalline driving circuit50, and controls the operational timing of the scanningline driving circuit40 according to the operation of the signalline driving circuit50.

The scanningline driving circuit40 is connected to thescanning line106, and has a function to output a scan signal to thescanning line106 to control between the conductive state (ON state) and the non-conductive state (OFF state) of the switchingtransistor101 included in theluminescent pixel100.

The signalline driving circuit50 is connected to thesignal line105, and has a function to apply, to theluminescent pixel100, a signal voltage based on a video signal.

Thedisplay unit60 includes a plurality ofluminescent pixels100 which are two-dimensionally arranged, and displays an image based on the video signal input to theluminescent display device10 from outside.

Next, the following describes the connection relationships and functions of the structural elements shown inFIG. 3.

The switchingtransistor101 is an example of a switching element in which the gate is connected to thescanning line106, one of the source and the drain is connected to thesignal line105, and the other one of the source and the drain is connected to acapacitor electrode102a of thecapacitor102. The switchingtransistor101 has a function to determine timing of applying the signal voltage at thesignal line105 to thecapacitor electrode102a of thecapacitor102. The switchingtransistor101 is, for example, an n-type thin-film transistor (n-type TFT), but may be a p-type TFT.

Thecapacitor102 is an example of the first capacitor and includes twocapacitor electrodes102a and102b. Thecapacitor electrode102a is connected to the gate of the drivingtransistor103, whereas thecapacitor electrode102b is connected to the higher-voltage-side power line107. Thecapacitor102 holds a charge corresponding to the signal voltage supplied from thesignal line105. In other words, thecapacitor102 is an example of a capacitive element used for setting a value of a driving current supplied to theorganic EL element104. For example, thecapacitor102 has a function to cause the drivingtransistor103 to supply the driving current to theorganic EL element104 even when the switchingtransistor101 is switched to the OFF state, until another signal voltage is applied.

The drivingtransistor103 is an example of a driving element in which the source is connected to the higher-voltage-side power line107 and the drain is connected to the anode of theorganic EL element104. The drivingtransistor103 coverts a voltage corresponding to a signal voltage applied between the gate and the source into a source-drain current corresponding to the applied signal voltage. The drivingtransistor103 then supplies the source-drain current to theorganic EL element104 as the driving current. The drivingtransistor103 is a p-type thin-film transistor (p-type TFT), for example.

Theorganic EL element104 is an example of a luminescent element which is driven to produce luminescence by a driving circuit which includes a thin-film transistor such as the drivingtransistor103. In theorganic EL element104, the anode is connected to the drain of the drivingtransistor103, and the cathode is connected to the lower-voltage-side power line108. Theorganic EL element104 produces luminescence when the drivingtransistor103 passes the driving circuit through theorganic EL element104. The luminescence intensity is controlled by a magnitude of the driving current; in other words, the signal voltage.

Thesignal line105 is connected to the signalline driving circuit50 and to each of luminescent pixels in the pixel column that includes theluminescent pixel100, and has a function to supply a signal voltage that determines the luminescence intensity. It is to be noted that theluminescent display device10 includes the same number ofsignal lines105 as the number of pixel columns.

Thescanning line106 is connected to the scanningline driving circuit40 and to each of luminescent pixels in the pixel row that includes theluminescent pixel100. With this, thescanning line106 has a function to supply a signal indicating timing of applying the signal voltage to each of the luminescent pixels in the pixel row that includes theluminescent pixel100. It is to be noted that theluminescent display device10 includes the same number ofscanning lines106 as the number of pixel rows.

Although not shown inFIG. 2 orFIG. 3, each of the higher-voltage-side power line107 and the lower-voltage-side power line108 is also connected to other luminescent pixels and to a voltage source. The potential difference between a voltage source VDD to which the higher-voltage-side power line107 is connected and a voltage source VEE to which the lower-voltage-side power line108 is connected has a magnitude which allows passage of a current which is sufficient to cause theorganic EL element104 to produce luminescence. It is to be noted that the lower-voltage-side power line108 may be grounded.

As shown in the above structure, theluminescent display device10 according toEmbodiment 1 includes thedisplay unit60 in which a plurality ofluminescent pixels100 are two-dimensionally arranged. Thedisplay unit60 displays video as theorganic EL elements104 in theluminescent pixels100 produce luminescence at the luminescence intensity according to the signal voltages.

The following describes the positional relationships between the elements included in theluminescent pixel100 according toEmbodiment 1.

FIG. 4 shows an example layout of theluminescent pixel100 according toEmbodiment 1.

As shown inFIG. 4, theluminescent pixel100 can be separated into a drivingcircuit region110 and aluminescent region120. In theluminescent region120, theorganic EL element104 is formed which produces luminescence according to the signal voltage supplied from thesignal line105. It is to be noted that theluminescent display device10 according toEmbodiment 1 is assumed as a bottom-emission luminescent display device. To be more specific, luminescence produced by theorganic EL element104 is directed toward the bottom surface of the substrate. In other words, the display surface of thedisplay unit60 is on the bottom surface side of the substrate.

The drivingcircuit region110 is the region of theluminescent pixel100 excluding theluminescent region120, and is a region in which the driving circuit driving theorganic EL element104 is formed. In thedriving circuit region110, the switchingtransistor101, thecapacitor102, and the drivingtransistor103 are formed.

FIG. 5 shows a cross-sectional view of theluminescent pixel100 according toEmbodiment 1. More specifically,FIG. 5 schematically shows a cross section A-A of theluminescent pixel100 shown inFIG. 4. The cross section A-A is a cross section showing the positional relationship between thecapacitor102 and the drivingtransistor103. For simplicity,FIG. 5 does not show thesignal line105 and the higher-voltage-side power line107.

As shown inFIG. 5, the drivingtransistor103 is formed on asubstrate210. The drivingtransistor103 includes asemiconductor layer220, agate insulating film230, agate electrode103g, asource electrode103s, and adrain electrode103d. Further, thecapacitor102 includes thecapacitor electrode102b, aninterlayer insulating film240, and thecapacitor electrode102a which functions also as thegate electrode103g. Further, aplanarizing film250 is formed on thecapacitor102.

Thesubstrate210 is, for example, a transparent substrate such as glass or quartz. Thesubstrate210 may be a flexible substrate such as a plastic. In the case of a top-emission luminescent display device, thesubstrate210 may be a semiconductor substrate such as a silicon substrate, or a compound semiconductor substrate made with a compound semiconductor such as a nitride semiconductor.

Although it has been described above that the drivingtransistor103 is formed on thesubstrate210, it may be formed above thesubstrate210. For example, a buffer layer may be formed on thesubstrate210 and the drivingtransistor103 may be formed on the buffer layer.

Thesemiconductor layer220 is a semiconductor layer formed on thesubstrate210 and includes achannel region221, asource region222, and adrain region223. For example, thesemiconductor layer220 is made with a doped inorganic semiconductor such as polysilicon, microcrystalline silicon, or amorphous silicon, or an organic semiconductor.

It is to be noted that the drivingtransistor103 is a p-type TFT, and thus, holes mainly contribute to the conduction in thechannel region221. That is to say, the above-described driving current flows as the holes move from thesource region222 to thedrain region223 according to voltages applied to thesource electrode103s, thedrain electrode103d, and thegate electrode103g.

Thegate insulating film230 is, for example, a film having insulating properties, such as a silicon oxide film (SiO_x). In the example shown inFIG. 5, thegate insulating film230 is formed on the entire surface of thesubstrate210 to cover thesemiconductor layer220, and through-holes are formed in the regions above thesource region222 and thedrain region223. Thegate insulating film230 is sufficient as long as it is formed on thechannel region221 at least.

Thegate electrode103g is a metal electrode formed on thegate insulating film230. For example, thegate electrode103g has a single-layer structure of a metal such as molybdenum or tungsten, an alloy of molybdenum and tungsten, or polysilicon, or has a laminated structure of polysilicon, and titanium and tungsten, or the like. It is to be noted that thegate electrode103g is connected to the source or drain of the switching transistor101 (not shown inFIG. 5). The most significant feature of the present invention is that thegate electrode103g also functions as thecapacitor electrode102a of thecapacitor102.

Thesource electrode103s is formed on thesource region222, and is made of a metal such as aluminum or copper or has a laminated structure of metals such as aluminum and molybdenum, for example. Thesource electrode103s is connected to the higher-voltage-side power line107 (not shown inFIG. 5). Further, as shown inFIG. 5, thesource electrode103s is connected to thecapacitor electrode102b of thecapacitor102 via the through-hole formed in theinterlayer insulating film240 and in thegate insulating film230.

Thedrain electrode103d is formed on thedrain region223, and is made of a metal such as aluminum or has a laminated structure of metals such as aluminum and molybdenum, for example. Thedrain electrode103d is connected to the anode of the organic EL element104 (not shown inFIG. 5).

Theinterlayer insulating film240 is formed on thegate electrode103g and is made with, for example, a silicon nitride film (SiN_x), a silicon oxide film, or the like. In the example shown inFIG. 5, theinterlayer insulating film240 is formed on the entire surface of thegate insulating film230 to cover thegate electrode103g, and through-holes are formed in the regions above thesource region222 and thedrain region223. Theinterlayer insulating film240 is sufficient as long as it is formed on thegate electrode103g at least.

It is to be noted that the thickness of theinterlayer insulating film240 is 100 to 1000 nm.

Thecapacitor electrode102b is an example of the first capacitor electrode and is formed on theinterlayer insulating film240 above thegate electrode103g. Put it differently, thecapacitor electrode102b is formed on theinterlayer insulating film240 in the region above thegate electrode103g. Thecapacitor electrode102b, together with thegate electrode103g that is theother capacitor electrode102a, constitutes thecapacitor102. For example, thecapacitor electrode102b is made of a metal such as aluminum or copper, or has a laminated structure of metals such as aluminum and molybdenum. In this example, thecapacitor electrode102b is connected to the higher-voltage-side power line107.

Further, thecapacitor electrode102b and thesource electrode103s form one layer and are connected to each other. More specifically, thecapacitor electrode102b is connected to thesource electrode103s via the through-hole formed in theinterlayer insulating film240. Preferably, thecapacitor electrode102b is made of the same material as that of thesource electrode103s. This makes it possible to form thecapacitor electrode102b and thesource electrode103s in the same process, thereby achieving reduction in the number of processes.

The area of the lower surface of thecapacitor electrode102b in the region above thegate electrode103g, which is thecapacitor electrode102a, is 30% to 100% of the area of the upper surface of thegate electrode103g. It is to be noted that thecapacitor electrode102b may be larger than thegate electrode103g. Further, the capacitance of thecapacitor102 is 0.1 to 10 pF.

Theplanarizing film250 is formed on thecapacitor102, and functions as a protection film which protects thecapacitor102 and the drivingtransistor103 and also functions as a planarizing film which planarizes the upper surfaces of thecapacitor102 and the drivingtransistor103. Theplanarizing film250 is made with, for example, a silicon oxide film (SiO_x), a silicon nitride film (SiN_x), or the like.

As shown in the above structure, thecapacitor102 uses thegate electrode103g as one of the capacitor electrodes. In other words, thecapacitor102 having thegate electrode103g as thecapacitor electrode102a is formed in the region above the drivingtransistor103.

As shown inFIG. 4, this makes it possible to form thecapacitor102 without a region, in theluminescent pixel100, dedicated to thecapacitor102. Therefore, it is possible to relatively flexibly design the area of thecapacitor102 or design the arrangement of the drivingtransistor103 and the switchingtransistor101. Alternatively, another capacitor can be added to thedriving circuit region110. As described above, with theluminescent display device10 according toEmbodiment 1, it is possible to increase the design flexibility. With this, for example, since theluminescent display device10 according toEmbodiment 1 is a bottom-emission luminescent display device, it is possible to ensure a wide area for theluminescent region120, reduce the density of the current flowing in theorganic EL element104, and ensure a longer luminescence lifetime for theluminescent display device10.

It is to be noted that the structure in which the capacitor is formed above the drivingtransistor103 as shown in the present embodiment can be applied to a driving circuit other than the circuit shown inFIG. 3. More specifically, the structure according to the present embodiment can be applied to a driving circuit having a circuit structure in which the gate of the drivingtransistor103 is electrically connected to one of two capacitor electrodes constituting the capacitor. The following describes some variations with reference to the drawings.

(Variation 1)

FIG. 6 shows a circuit structure of aluminescent pixel300 according to a variation ofEmbodiment 1. Theluminescent pixel300 shown inFIG. 6 includes switchingtransistors101,313,314 and315, the drivingtransistor103,capacitors311 and312, theorganic EL element104, thesignal line105, scanninglines106,316,317 and318, the higher-voltage-side power line107, the lower-voltage-side power line108, and a referencevoltage power line319. It is to be noted that the same structural elements as that of theluminescent pixel100 shown inFIG. 3 are given the same reference signs and the descriptions thereof are omitted below.

The switchingtransistor313 is an example of a switching element in which the gate is connected to thescanning line316, one of the source and the drain is connected to the referencevoltage power line319, and the other one of the source and the drain is connected to one of the source and the drain of the switchingtransistor101. The switchingtransistor313 has a function to initialize the gate potential of the drivingtransistor103, that is, a function to set the gate potential of the drivingtransistor103 to a reference potential Vref.

To be more specific, the switchingtransistor313 is turned on by a scanning signal supplied from thescanning line316, and supplies the reference potential Vref to second electrodes of the capacitors. It is to be noted that the switchingtransistor313 is an n-type TFT, for example.

The switchingtransistor314 is an example of a switching element in which the gate is connected to thescanning line317, one of the source and the drain is connected to the gate of the drivingtransistor103, and the other one of the source and the drain is connected to the drain of the drivingtransistor103. The switchingtransistor314 has a function to detect a threshold voltage of the drivingtransistor103.

More specifically, for example, the switchingtransistor314 is turned on by a scanning signal supplied from thescanning line317, and short-circuits the gate and the drain of the drivingtransistor103. Accordingly, the threshold voltage of the drivingtransistor103 is generated at the gate electrode of the drivingtransistor103. The switchingtransistor314 is an n-type TFT, for example.

The switchingtransistor315 is an example of a switching element in which the gate is connected to thescanning line318, one of the source and the drain is connected to the drain of the drivingtransistor103, and the other one of the source and the drain is connected to the anode of theorganic EL element104. The switchingtransistor315 has a function to determine timing of supplying the driving current to theorganic EL element104.

More specifically, for example, the switchingtransistor315 is turned on by a scanning signal supplied from thescanning line318, and when the drivingtransistor103 is turned on while the switchingtransistor315 is on, the driving current is supplied to theorganic EL element104. To put it differently, the driving current is not supplied to theorganic EL element104 while the switchingtransistor315 is off, regardless of the operation of the drivingtransistor103. It is to be noted that the switchingtransistor315 is an n-type TFT, for example.

Thecapacitor311 includes twocapacitor electrodes311a and311b. Thecapacitor electrode311a is connected to the referencevoltage power line319, whereas thecapacitor electrode311b is connected to one of the source and the drain of the switchingtransistor101. Thecapacitor electrode311b is also connected to the gate of the drivingtransistor103 via thecapacitor312. Thecapacitor311 holds a charge corresponding to the signal voltage supplied from thesignal line105.

Thecapacitor312 is an example of the first capacitor, and includes twocapacitor electrodes312a and312b. Thecapacitor electrode312b is connected to one of the source and the drain of the switchingtransistor101, whereas thecapacitor electrode312a is connected to the gate of the drivingtransistor103. Thecapacitor312 holds a charge corresponding to the threshold voltage of the drivingtransistor103.

The scanning lines316,317 and318 are connected to the scanningline driving circuit40 and to each of luminescent pixels in the pixel column that includes theluminescent pixel300. Thescanning line316 has a function to supply a reference voltage for detecting the threshold voltage of the drivingtransistor103 which is included in each of the luminescent pixels in the pixel row that includes theluminescent pixel300.

Thescanning line317 has a function to supply a signal indicating timing of detecting the threshold voltage of the drivingtransistor103 which is included in each of the luminescent pixels in the pixel row that includes theluminescent pixel300. Thescanning line318 has a function to supply: a signal indicating timing of supplying the driving current to theorganic EL element104 which is included in each of the luminescent pixels in the pixel row that includes theluminescent pixel300; and a signal indicating timing of detecting the threshold voltage of the drivingtransistor103.

It is to be noted that theluminescent display device10 includes the same number ofscanning lines316,317 and318 as the number of pixel rows.

The referencevoltage power line319 is also connected to other luminescent pixels and to a voltage source which supplies a predetermined reference voltage. With this, the potential at the referencevoltage power line319 is maintained at the reference potential Vref.

FIG. 7 shows a partial cross-sectional view of theluminescent pixel300 according toVariation 1 ofEmbodiment 1. Specifically,FIG. 7 shows the structure in which thecapacitor312 and the drivingtransistor103 are arranged. It is to be noted that the cross-sectional structure of the drivingtransistor103 is the same as the cross-sectional structure shown inFIG. 5, and thus the description thereof is omitted below.

As shown inFIG. 7, thecapacitor electrode312b of thecapacitor312 is formed on theinterlayer insulating film240. Thegate electrode103g functions also as thecapacitor electrode312a of thecapacitor312.

Thecapacitor electrode312b is an example of the first capacitor electrode, and is not connected to thesource electrode103s or thedrain electrode103d of the drivingtransistor103. Thecapacitor electrode312b is connected to one of the source and the drain of the switchingtransistor101 and to thecapacitor electrode311b (not shown inFIG. 7).

As described above, thecapacitor electrode312b of thecapacitor311 formed on the drivingtransistor103 does not have to be connected to each electrode of the drivingtransistor103. That is to say, the structure according to the present embodiment can be applied as long as one of the two electrodes constituting the capacitor is connected to thegate electrode103g of the drivingtransistor103.

(Variation 2)

FIG. 8 shows a circuit structure of aluminescent pixel400 according to another variation ofEmbodiment 1. Theluminescent pixel400 shown inFIG. 8 is different from theluminescent pixel300 shown inFIG. 6 in that theluminescent pixel400 includes acapacitor411 instead of thecapacitor311 and a switchingtransistor413 instead of the switchingtransistor313. Hereinafter, the same structural elements as that of theluminescent pixel300 shown inFIG. 6 are given the same reference signs and the descriptions thereof are omitted below.

Thecapacitor411 is an example of the first capacitor, and includes twocapacitor electrodes411a and411b. Thecapacitor electrode411a is connected to thegate electrode103g of the drivingtransistor103, whereas thecapacitor electrode411b is connected to, for example, the higher-voltage-side power line107. Thecapacitor411 holds a charge corresponding to the signal voltage supplied from thesignal line105 and to the threshold voltage of the driving transistor.

The switchingtransistor413 is an example of a switching element in which the gate is connected to thescanning line316, one of the source and the drain is connected to the higher-voltage-side power line107, and the other one of the source and the drain is connected to one of the source and the drain of the switchingtransistor101 and to thecapacitor electrode312b of thecapacitor312. The switchingtransistor413 has a function to initialize thecapacitor312 and thecapacitor411.

More specifically, the switchingtransistor413 performs the initialization such that thecapacitor312 and thecapacitor411 hold the threshold voltage of the drivingtransistor103 when the switchingtransistor413 is turned on by a scanning signal supplied from thescanning line316, the potential at thecapacitor electrode312b of thecapacitor312 is set to VDD, and the switchingtransistor314 is turned on by a scanning signal supplied from thescanning line317. It is to be noted that the switchingtransistor413 is an n-type TFT, for example.

FIG. 9 shows a cross-sectional view of theluminescent pixel400 according to Variation 2 ofEmbodiment 1. Specifically,FIG. 9 shows the structure in which thecapacitor312, thecapacitor411, and the drivingtransistor103 are arranged. It is to be noted that the cross-sectional structure of the drivingtransistor103 is the same as the cross-sectional structure shown inFIG. 5, and thus the description thereof is omitted below.

As shown inFIG. 9, thecapacitor electrode312b of thecapacitor312 and thecapacitor electrode411b of thecapacitor411 are formed on theinterlayer insulating film240. Thegate electrode103g functions also as thecapacitor electrode312a of thecapacitor312 and thecapacitor electrode411a of thecapacitor411.

Thecapacitor electrode411b is an example of the first capacitor electrode. Thecapacitor electrode411b and thesource electrode103s of the drivingtransistor103 form one layer and are connected to each other. More specifically, thecapacitor electrode411b is connected to thesource electrode103s via the through-hole formed in theinterlayer insulating film240.

It is to be noted that thecapacitor electrode312b, thecapacitor electrode411b, and thesource electrode103s are preferably made of the same material. This makes it possible to form thecapacitor electrode312b, thecapacitor electrode411b, and thesource electrode103s in the same process, thereby achieving reduction in the number of processes.

As described above, theluminescent display device10 according to Variation 2 ofEmbodiment 1 includes a plurality of first capacitor electrodes, and each of the plurality of first capacitor electrodes and thegate electrode103g constitute the first capacitor. Although the examples shown inFIG. 8 andFIG. 9 have illustrated two first capacitor electrodes, there may be three or more first capacitor electrodes formed on theinterlayer insulating film240 in the region above thegate electrode103g.

As described above, in theluminescent display device10 according toEmbodiment 1 and the variations thereof, the first capacitor is constituted by thegate electrode103g of the drivingtransistor103 included in the driving circuit and the first capacitor electrode formed above thegate electrode103g. The first capacitor having such a structure can be used as, for example, a capacitive element for setting a value of the driving current supplied to theorganic EL element104.

This enables efficient use of the limited region within theluminescent pixel100. That is to say, the design flexibility can be increased. Accordingly, theluminescent display device10 according to the present embodiment provides an advantageous effect of ensuring a wide region for theluminescent region120, for example.

It is to be noted that theluminescent display device10 according toEmbodiment 1 may further include a second capacitor which is electrically connected to thecapacitor102 in parallel. For example, the second capacitor includes an upper second capacitor electrode and a lower second capacitor electrode. One of the upper second capacitor electrode and the lower second capacitor electrode is connected to thegate electrode103g, and the other one is electrically connected to one of thesource electrode103s and thedrain electrode103d.

More specifically, the lower second capacitor electrode and thegate electrode103g may form one layer, and the upper second capacitor electrode and an electrically-connected one of thesource electrode103s and thedrain electrode103d may form one layer. Here, thecapacitor electrode102a of thecapacitor102 is electrically connected to the upper second capacitor electrode.

Embodiment 2

The luminescent display device according to Embodiment 2 includes a switching transistor, a driving transistor, and a capacitor, and the gate electrode of the switching transistor is one of two capacitor electrodes constituting the capacitor. Thus, the capacitor is formed in the region above the switching transistor.

The luminescent display device according to Embodiment 2 is different from theluminescent display device10 according toEmbodiment 1 in circuit structure of each luminescent pixel included in the display unit and in arrangement of elements constituting each luminescent pixel. In other words, the luminescent display device according to Embodiment 2 has the same electrical structure as that of theluminescent display device10 according toEmbodiment 1 shown inFIG. 2. Thus, the description of the electrical structure of the luminescent display device according to Embodiment 2 is omitted, and the following description centers on the circuit structure of each luminescent pixel and on the arrangement of the elements constituting each luminescent pixel.

FIG. 10 shows a circuit structure of aluminescent pixel500 included in a display unit according to Embodiment 2. Theluminescent pixel500 inFIG. 10 includes switchingtransistors501,506,507 and508,capacitors502 and505, a drivingtransistor503, anorganic EL element504, asignal line509, scanninglines510,511,512 and513, a higher-voltage-side power line514, a lower-voltage-side power line515, and a referencevoltage power line516.

The switchingtransistor501 is an example of a switching element in which the gate is connected to thescanning line510, one of the source and the drain is connected to thesignal line509, and the other one of the source and the drain is connected to acapacitor electrode502a of thecapacitor502 and to the gate of the drivingtransistor503. The switchingtransistor501 has a function to determine timing of applying a signal voltage at thesignal line509 to thecapacitor electrode502a of thecapacitor502. The switchingtransistor501 is an n-type TFT, for example.

Thecapacitor502 is an example of the first capacitor corresponding to the drivingtransistor503, and includes twocapacitor electrodes502a and502b. Thecapacitor electrode502a is connected to the gate of the drivingtransistor503, whereas thecapacitor electrode502b is connected to acapacitor electrode505b of thecapacitor505 and to the source or drain of the switchingtransistor507. Thecapacitor502 holds a charge corresponding to the signal voltage supplied from thesignal line509 and to a threshold voltage of the drivingtransistor503. In other words, thecapacitor502 is an example of a capacitive element for setting a value of a driving current supplied to theorganic EL element504.

The drivingtransistor503 is an example of a driving element in which the drain is connected to the higher-voltage-side power line514, and the source is connected to the anode of theorganic EL element504 via the switchingtransistor508. The drivingtransistor503 coverts a voltage corresponding to a signal voltage applied between the gate and the source into a source-drain current corresponding to that signal voltage. The drivingtransistor503 is an n-type TFT, for example.

Theorganic EL element504 is an example of a luminescent element in which the anode is connected to the source of the drivingtransistor503 via the switchingtransistor508, and the cathode is connected to the lower-voltage-side power line515. Theorganic EL element504 produces luminescence when the drivingtransistor503 passes the driving circuit through theorganic EL element504.

Thecapacitor505 is an example of the first capacitor corresponding to the switchingtransistor508, and includes twocapacitor electrodes505a and505b. Thecapacitor electrode505a is connected to thescanning line513, whereas thecapacitor electrode505b is connected to thecapacitor electrode502b and to one of the source and the drain of the switchingtransistor507. Thecapacitor505 is an example of a capacitive element for adjusting the amount of voltage held by thecapacitor502 which is a capacitive element which holds a data voltage applied from thesignal line509.

The switchingtransistor506 is an example of a switching element in which the gate is connected to thescanning line511, one of the source and the drain is connected to the referencevoltage power line516, and the other one of the source and the drain is connected to the gate of the drivingtransistor503. The switchingtransistor506 has a function to apply a reference voltage Vref to the gate of the drivingtransistor503. It is to be noted that the switchingtransistor506 is an n-type TFT, for example.

The switchingtransistor507 is an example of a switching element in which the gate is connected to thescanning line512, one of the source and the drain is connected to thecapacitor electrode502b of thecapacitor502, and the other one of the source and the drain is connected to the source of the drivingtransistor503. The switchingtransistor507 has a function to disconnect thecapacitor502 and the source of the drivingtransistor503 when applying a signal voltage to thecapacitor502. It is to be noted that the switchingtransistor507 is an n-type TFT, for example.

The switchingtransistor508 is an example of a switching element in which the gate is connected to thescanning line513, one of the source and the drain is connected to the source of the drivingtransistor503, and the other one of the source and the drain is connected to the anode of theorganic EL element504. The switchingtransistor508 has a function to determine timing of supplying the driving current to theorganic EL element504. It is to be noted that the switchingtransistor508 is an n-type TFT, for example.

Thesignal line509 is connected to the signal line driving circuit and to each of luminescent pixels in the pixel column that includes theluminescent pixel500, and has a function to supply a signal voltage that determines the luminescence intensity. It is to be noted that the luminescent display device according to Embodiment 2 includes the same number ofsignal lines509 as the number of pixel columns.

The scanning lines510,511,512 and513 are connected to the scanning line driving circuit and to each of luminescent pixels in the pixel row that includes theluminescent pixel500. Thescanning line510 has a function to supply a signal indicating timing of applying the signal voltage to each of the luminescent pixels in the pixel row that includes theluminescent pixel500.

Thescanning line511 has a function to supply a signal indicating timing of applying a reference voltage Vref to the gate of the drivingtransistor503 in each of the luminescent pixels in the pixel row that includes theluminescent pixel500. Thescanning line512 has a function to supply a signal indicating timing of disconnecting thecapacitor502 and the source of the drivingtransistor503 in each of the luminescent pixels in the pixel row that includes theluminescent pixel500. Thescanning line513 has a function to supply a signal indicating timing of supplying the driving current to theorganic EL element504 in each of the luminescent pixels in the pixel row that includes theluminescent pixel500.

It is to be noted that the luminescent display device according to Embodiment 2 includes the same number ofscanning lines510,511,512 and513 as the number of pixel rows.

Although not shown inFIG. 10, the higher-voltage-side power line514, the lower-voltage-side power line515, and the referencevoltage power line516 are each connected to other luminescent pixels and to a voltage source. The potential difference between the voltage source to which the higher-voltage-side power line514 is connected and the voltage source to which the lower-voltage-side power line515 is connected has a magnitude which allows a flow of a current sufficient for theorganic EL element504 to produce luminescence. It is to be noted that the lower-voltage-side power line515 may be grounded.

FIG. 11 shows an example layout of theluminescent pixel500 according to Embodiment 2. The luminescent display device according to Embodiment 2 is assumed as a top-emission luminescent display device. To be more specific, the luminescence produced by theorganic EL element504 is directed toward the top surface of the substrate. In other words, the display surface of the display unit is on the top surface side of the substrate.

In theluminescent pixel500, the luminescent region in which theorganic EL element504 is formed is the same as the driving circuit region. That is to say, the luminescent region is formed above the driving circuit region.

As shown inFIG. 11, the drivingtransistor503 and thecapacitor502 are formed in the same region in the plane to overlap each other, and the switchingtransistor508 and thecapacitor505 are formed in the same region in the plane to overlap each other. The structure according to the present embodiment can be applied to such a circuit structure as above in which the gate of a thin-film transistor such as the drivingtransistor503 or the switchingtransistor508 is electrically connected with a capacitor electrode of a capacitor.

FIG. 12 shows a cross-sectional view of theluminescent pixel500 according to Embodiment 2. More specifically,FIG. 12 shows a structure in which the switchingtransistor508, thecapacitor505, and theorganic EL element504 are arranged.

It is to be noted that the structure of the switchingtransistor508 is the same as that of the drivingtransistor103 shown inFIG. 7. To be more specific, asubstrate610, asemiconductor layer620, agate insulating film630, aninterlayer insulating film640, agate electrode508g, asource electrode508s, and adrain electrode508d which are shown inFIG. 12 correspond to thesubstrate210, thesemiconductor layer220, thegate insulating film230, theinterlayer insulating film240, thegate electrode103g, thesource electrode103s, and thedrain electrode103d which are shown inFIG. 7, respectively. Further, achannel region621, asource region622, and adrain region623 included in thesemiconductor layer620 correspond to thechannel region221, thesource region222, and thedrain region223 included in thesemiconductor layer220, respectively.

As shown inFIG. 12, thecapacitor electrode505b of thecapacitor505 is an example of the first capacitor electrode, and thecapacitor electrode505b and thesource electrode508s form one layer and are connected to each other. It is to be noted that instead of being connected to thesource electrode508s, thecapacitor electrode505b may be electrically connected to thedrain electrode508d.

Since the luminescent display device according to Embodiment 2 is a top-emission luminescent display device, theorganic EL element504 is formed in a layer above thecapacitor505. More specifically, as shown inFIG. 12, theorganic EL element504 is formed above thecapacitor505 with aplanarizing film650 therebetween. Theorganic EL element504 includes an anode504a, aluminescent layer504b, and atransparent cathode504c.

Theplanarizing film650 is made with a silicon nitride film, for example.

The anode504a is a light-reflective electrode and is made of a metal such as aluminum, for example. The anode504a has a function to reflect luminescence produced by theluminescent layer504b. The anode504a is the anode electrode of theorganic EL element504, and is connected to the source of the drivingtransistor503 via the switchingtransistor508 as shown inFIG. 10.

Theluminescent layer504b is a luminescent layer which is formed between the anode504a and thetransparent cathode504c which is transparent or semitransparent, and produces luminescence due to recombination of the holes and electrons injected from the anode504a and thetransparent cathode504c, respectively. It is to be noted that theluminescent layer504b may include a hole transport layer, a hole injection layer, an electron transport layer, an electron injection layer, and so on.

Thetransparent cathode504c is a light-transmissive electrode and is made with a transparent conductive oxide film such as an indium tin oxide (ITO), for example. Thetransparent cathode504c is the cathode electrode of theorganic EL element504, and is connected to the lower-voltage-side power line515 as shown inFIG. 10.

As described above, with the luminescent display device according to Embodiment 2, thecapacitor505 is constituted by thegate electrode508g of the switchingtransistor508 included in the driving circuit and thecapacitor electrode505b formed above thegate electrode508g. Thecapacitor505 having such a structure can be used as, for example, a capacitive element for: initializing a capacitive element for setting the value of the driving current supplied to theorganic EL element504; and adjusting the amount of voltage to be held by the capacitive element out of the data voltage applied from thesignal line509.

Thus, the structure of the present embodiment can be applied to a driving circuit having a circuit structure in which the gate electrode of a switching transistor and one of the capacitor electrodes of a capacitor are electrically connected. As a result, it is possible to reduce the region dedicated to the capacitor, and thus the design flexibility of the driving circuit can be increased.

Although the luminescent display device according to the present invention has been described above based on some exemplary embodiments, the present invention is not intended to be limited to such embodiments. Those skilled in the art may arrive at many modifications to the above exemplary embodiments and at various embodiments implemented by combining the structural elements of different embodiments without materially departing from the novel teachings and advantages of the present invention. Accordingly, all such modifications and embodiments are intended to be included within the scope of the present invention.

For example, the present invention is applicable to a circuit having a circuit structure in which the gate of a thin-film transistor included in a driving circuit is connected with one of the electrodes of a capacitor. Although the above embodiments have described the structure in which the gate of a driving transistor or a switching transistor is connected with one of the electrodes of a capacitor, the circuit structure and so on is not limited to the above description.

Further, the above embodiments have described the switching transistors as the n-type transistors which are turned on when a positive voltage is applied to the gate of the switching transistors. However, the same advantageous effect as that of the above-described embodiments can be provided also by a video display device in which the switching transistors are p-type transistors and the polarity of the scanning lines is reversed. Furthermore, although the above description explained that the lower electrode is the anode and the upper electrode is the cathode, it may surely be that the lower electrode is the cathode and the upper electrode is the anode.

Moreover, for example, the luminescent display device according to the present invention is built in a television set as shown inFIG. 13. With the built-in luminescent display device according to the present invention, it is possible to provide a television set capable of high-precision image display that reflects video signals.

Furthermore, the luminescent display device according to the present invention may include a second capacitor which is electrically connected in parallel with a first capacitor having the gate electrode of a thin-film transistor as the lower electrode as described above.

FIG. 14 shows an example layout of a luminescent pixel in another variation of the luminescent display device according to the present invention. InFIG. 14, the same structural elements as that of the conventional luminescent display device shown inFIG. 1 are given the same reference signs and the descriptions thereof are omitted below.

As shown inFIG. 14, theluminescent pixel700 includes afirst capacitor708 and acapacitor702 which is a second capacitor. Thefirst capacitor708 is formed on the drivingtransistor703 and includes an upper electrode and a lower electrode. The lower electrode of thefirst capacitor708 functions also as the gate electrode of the drivingtransistor703. Thecapacitor702 which is the second capacitor includes an upper second capacitor electrode and a lower second capacitor electrode.

The upper electrode of thefirst capacitor708 is electrically connected to the upper second capacitor electrode of thecapacitor702. More specifically, as shown inFIG. 14, the upper electrode of thefirst capacitor708, the upper second capacitor electrode of thecapacitor702, thepower line707, and one of the source electrode and the drain electrode of the drivingtransistor703 form one layer, and the upper electrode of thefirst capacitor708 is electrically connected to the one of the source electrode and the drain electrode of the drivingtransistor703.

The lower electrode of thefirst capacitor708 functions as the gate electrode of the drivingtransistor703 as described above, and is electrically connected to the lower second capacitor electrode of thecapacitor702. More specifically, as shown inFIG. 14, the lower second capacitor electrode of thecapacitor702 and the gate electrode which is the lower electrode of thefirst capacitor708 form one layer and are electrically connected.

The above structure makes it possible to efficiently use the region above the drivingtransistor703 and to increase the capacity of thecapacitor702.

INDUSTRIAL APPLICABILITY

The luminescent display device according to the present invention is applicable to various display devices such as television sets, personal computers, and mobile phones.

Claims (28)

What is claimed is:

1. A luminescent display device, comprising:

a substrate; and

a plurality of pixels above the substrate,

each of the pixels including:

a thin film transistor above the substrate, the thin film transistor including:

a semiconductor layer comprising a channel region, a source region, and a drain region;

a source electrode electrically connected to the source region of the semiconductor layer; and

a drain electrode electrically connected to the drain region of the semiconductor layer;

a lower electrode above the substrate, the lower electrode including a first portion and a second portion, the first portion of the lower electrode being provided in a region in which the thin film transistor is provided, the first portion of the lower electrode comprising a gate electrode of the thin film transistor, the second portion of the lower electrode being provided in a region other than the region in which the thin-film transistor is provided the lower electrode, including the first portion and the second portion, comprising one continuous layer;

an interlayer insulating film on the lower electrode;

an upper electrode on the interlayer insulating film, the upper electrode including a first portion and a second portion, the upper electrode, including the first portion and the second portion, comprising one continuous layer, the first portion of the upper electrode comprising a capacitor electrode directly above the gate electrode, the first portion of the upper electrode further comprising the source electrode, the capacitor electrode and the source electrode being connected via a through-hole in the interlayer insulating film; and

a luminescent element configured to be driven by a driver to produce luminescence, the driver including the thin film transistor,

wherein the first portion of the upper electrode and the first portion of the lower electrode comprise a first capacitance, and the second portion of the upper electrode and the second portion of the lower electrode comprise a second capacitance, and

the capacitor electrode extends from the second portion of the upper electrode to be directly above the gate electrode, with the upper electrode including a physical separation that overlaps the semiconductor layer and that is between the capacitor electrode and the source electrode.

2. The luminescent display device according toclaim 1,

wherein an area of a lower surface of the first portion of the upper electrode, in the region in which the thin film transistor is provided, is approximately 30% to approximately 100% of an area of an upper surface of the gate electrode.

3. The luminescent display device according toclaim 1, wherein the semiconductor layer comprises polysilicon.

4. The luminescent display device according toclaim 1,

wherein the first capacitance is approximately 0.1 pF to approximately 10 pF.

5. The luminescent display device according toclaim 1,

wherein the luminescent display device is a top-emission luminescent display device, and

the luminescent element is in a layer above the upper electrode.

6. The luminescent display device according toclaim 1,

wherein the luminescent display device is a bottom-emission luminescent display device, and

the thin-film transistor, the lower electrode, and the upper electrode are in a region other than a luminescent region in which the luminescent element is disposed.

7. The luminescent display device according toclaim 1,

wherein the one continuous layer of the upper electrode includes the source electrode of the thin film transistor.

8. The luminescent display device according toclaim 7, further comprising:

a power line connected to the one of the source electrode and the drain electrode of the thin film transistor,

wherein the one continuous layer of the upper electrode further includes the power line.

9. A luminescent display device, comprising:

a substrate; and

a plurality of pixels above the substrate,

each of the pixels including:

a thin film transistor above the substrate, the thin film transistor including:

a semiconductor layer comprising a channel region, a source region, and a drain region;

a source electrode configured to be electrically connected to the source region of the semiconductor layer; and

a drain electrode configured to be electrically connected to the drain region of the semiconductor layer;

a lower electrode above the substrate, the lower electrode including a first portion and a second portion, the first portion of the lower electrode being provided in a region in which the thin film transistor is provided, the first portion of the lower electrode comprising a gate electrode of the thin film transistor, the second portion of the lower electrode being provided in a region other than the region in which the thin-film transistor is provided, the lower electrode, including the first portion and the second portion, comprising one continuous layer;

an interlayer insulating film above the lower electrode;

an upper electrode, contacting the interlayer insulating film, which is configured to be electrically connected to one of the source region and the drain region of the semiconductor layer via a through-hole in the interlayer insulating film, the upper electrode including a first portion and a second portion, the upper electrode, including the first portion and the second portion, comprising one continuous layer, the first portion of the upper electrode overlapping the first portion of the lower electrode to form a first capacitance, the second portion of the upper electrode overlapping the second portion of the lower electrode to form a second capacitance; and

a luminescent element configured to be driven by a driver to produce luminescence, the driver including the thin film transistor,

wherein the first portion of the upper electrode extends from the second portion of the upper electrode to overlap the first portion of the lower electrode to form the first capacitance, with the upper electrode including a physical separation that overlaps the semiconductor layer and that is between the first portion of the upper electrode and a portion of the upper electrode that is configured to be electrically connected to the one of the source region or the drain region.

10. The luminescent display device according to claim 9, wherein an area of a lower surface of the first portion of the upper electrode, in the region in which the thin film transistor is provided, is approximately 30% to approximately 100% of an area of an upper surface of the gate electrode.

11. The luminescent display device according to claim 9, wherein the semiconductor layer comprises polysilicon.

12. The luminescent display device according to claim 9, wherein the first capacitance is approximately 0.1 pF to approximately 10 pF.

13. The luminescent display device according to claim 9, wherein the luminescent display device is a top-emission luminescent display device, and the luminescent element is in a layer above the upper electrode.

14. The luminescent display device according to claim 9, wherein a part of the upper electrode constitutes one of the source electrode and the drain electrode.

15. The luminescent display device according to claim 14, wherein the first portion of the upper electrode, the second portion of the upper electrode, and the part of the upper electrode which constitutes the one of the source electrode and the drain electrode comprise one continuous layer.

16. The luminescent display device according to claim 15, wherein the first portion of the upper electrode is connected to the one of the source electrode and the drain electrode via the through-hole in the interlayer insulating film.

17. The luminescent display device according to claim 9, wherein the first portion of the upper electrode is configured to be electrically connected to one of the source electrode and the drain electrode.

18. The luminescent display device according to claim 17, wherein the first portion of the upper electrode, the second portion of the upper electrode, and the one of the source electrode and the drain electrode comprise one continuous layer.

19. The luminescent display device according to claim 18, wherein the first portion of the upper electrode is connected to the source electrode via the through-hole in the interlayer insulating film.

20. The luminescent display device according to claim 9, wherein the first portion of the upper electrode, the second portion of the upper electrode, and one of the source electrode and the drain electrode comprise one continuous layer.

21. A luminescent display device, comprising:

a substrate; and

a plurality of pixels above the substrate,

each of the pixels including:

a driving transistor above the substrate;

a semiconductor layer comprising a channel region, a source region, and a drain region;

a source electrode configured to be electrically connected to the source region of the semiconductor layer;

a drain electrode configured to be electrically connected to the drain region of the semiconductor layer;

a lower electrode above the substrate, the lower electrode including a first portion and a second portion, the first portion of the lower electrode being provided in a region in which the driving transistor is provided, the first portion of the lower electrode comprising a gate electrode of the driving transistor, the second portion of the lower electrode being provided in a region other than the region in which the driving transistor is provided, the lower electrode, including the first portion and the second portion, comprising one continuous layer;

an interlayer insulating film above the lower electrode;

an upper electrode, contacting the interlayer insulating film, which is configured to be electrically connected to one of the source region and the drain region of the semiconductor layer via a through-hole in the interlayer insulating film, the upper electrode including a first portion and a second portion, the upper electrode, including the first portion and the second portion, comprising one continuous layer, the first portion of the upper electrode overlapping the first portion of the lower electrode to form a first capacitance, the second portion of the upper electrode overlapping the second portion of the lower electrode to form a second capacitance; and

a luminescent element configured to be driven by a driver to produce luminescence, the driver including the driving transistor,

wherein the first portion of the upper electrode extends from the second portion of the upper electrode to overlap the first portion of the lower electrode to form the first capacitance, with the upper electrode including a physical separation that overlaps the semiconductor layer and that is between the first portion of the upper electrode and a portion of the upper electrode that is configured to be electrically connected to the one of the source region or the drain region.

22. A luminescent display device, comprising:

a substrate; and

a plurality of pixels above the substrate,

each of the pixels including:

a thin film transistor above the substrate, the thin film transistor including:

a semiconductor layer comprising a channel region, a source region, and a drain region;

a source electrode configured to be electrically connected to the source region of the semiconductor layer; and

a drain electrode configured to be electrically connected to the drain region of the semiconductor layer;

a lower electrode above the substrate, the lower electrode including a first portion and a second portion, the first portion of the lower electrode being provided in a region in which the thin film transistor is provided, the first portion of the lower electrode comprising a gate electrode of the thin film transistor, the second portion of the lower electrode being provided in a region other than the region in which the thin-film transistor is provided, the lower electrode, including the first portion and the second portion, comprising one continuous layer;

an interlayer insulating film above the lower electrode;

an upper electrode contacting the interlayer insulating film, the upper electrode including a first portion and a second portion, the upper electrode, including the first portion and the second portion, comprising one continuous layer, the first portion of the upper electrode being above the gate electrode, a part of the upper electrode being connected to the source electrode, the part of the upper electrode and the source electrode being connected via a through-hole in the interlayer insulating film; and

a luminescent element configured to be driven by a driver to produce luminescence, the driver including the thin film transistor,

wherein the first portion of the upper electrode and the first portion of the lower electrode form a first capacitance in a region corresponding to the channel region,

the second portion of the upper electrode and the second portion of the lower electrode form a second capacitance in a region other than the region corresponding to the channel region, and

the first portion of the upper electrode extends from the second portion of the upper electrode to be above the gate electrode, with the upper electrode including a physical separation that is above the semiconductor layer and that is between the first portion of the upper electrode and the part of the upper electrode that is connected to the source electrode.

23. The luminescent display device according to claim 22, wherein an area of a lower surface of the first portion of the upper electrode, which is above the gate electrode, is approximately 30% to approximately 100% of an area of an upper surface of the gate electrode.

24. The luminescent display device according to claim 22, wherein the semiconductor layer comprises polysilicon.

25. The luminescent display device according to claim 22, wherein the first capacitance is approximately 0.1 pF to approximately 10 pF.

26. The luminescent display device according to claim 22, wherein the luminescent display device is a top-emission luminescent display device, and the luminescent element is in a layer above the upper electrode.

27. The luminescent display device according to claim 22, wherein the first portion of the upper electrode, the second portion of the upper electrode, and the source electrode comprise one continuous layer.

28. A luminescent display device, comprising:

a substrate; and

a plurality of pixels above the substrate,

each of the pixels including:

a driving transistor above the substrate;

a semiconductor layer comprising a channel region, a source region, and a drain region;

a source electrode configured to be electrically connected to the source region of the semiconductor layer;

a drain electrode configured to be electrically connected to the drain region of the semiconductor layer;

a lower electrode above the substrate, the lower electrode including a first portion and a second portion, the first portion of the lower electrode being provided in a region in which the driving transistor is provided, the first portion of the lower electrode comprising a gate electrode of the driving transistor, the second portion of the lower electrode being provided in a region other than the region in which the driving transistor is provided, the lower electrode, including the first portion and the second portion, comprising one continuous layer;

an interlayer insulating film above the lower electrode;

an upper electrode contacting the interlayer insulating film, the upper electrode including a first portion and a second portion, the upper electrode, including the first portion and the second portion, comprising one continuous layer, the first portion of the upper electrode being above the gate electrode, a part of the upper electrode being connected to the source electrode, the part of the upper electrode and the source electrode being connected via a through-hole in the interlayer insulating film; and

a luminescent element configured to be driven by a driver to produce luminescence, the driver including the driving transistor,

wherein the first portion of the upper electrode and the first portion of the lower electrode form a first capacitance in a region corresponding to the channel region,

the second portion of the upper electrode and the second portion of the lower electrode form a second capacitance in a region other than the region corresponding to the channel region, and

the first portion of the upper electrode extends from the second portion of the upper electrode to be above the gate electrode to form the first capacitance, with the upper electrode including a physical separation that is above the semiconductor layer and that is between the first portion of the upper electrode and the part of the upper electrode that is connected to the source electrode.

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