US20080043166A1 - Multi-level layer - Google Patents

Abstract

Various methods and apparatus relating to a multi-level layer are disclosed.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION
• The present application is related to co-pending U.S. patent application Ser. No. 11/243,614,000 on Oct. 5, 2005 by Bradley D. Chung et al. and entitled MULTI-LEVEL LAYER.
BACKGROUND
• Applications sometimes require a layer or structure having distinct levels or thicknesses. Existing methods for fabricating such multiple levels require a relatively large number of process steps, increasing fabrication costs and complexity.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIGS. 1-4 are side elevational views schematically illustrating one example of a method for forming a multi-level layer according to one example embodiment.
• FIG. 5A is a side elevational view schematically illustrating an alternative method for forming the multi-level layer ofFIG. 4 according to one example embodiment.
• FIG. 5B is a side elevational view schematically illustrating another method for forming the multi-level layer ofFIG. 4 according to one example embodiment.
• FIG. 6 is a graph illustrating a percent thickness change as a function of different heating according to one example embodiment.
• FIG. 7 is a side elevational view schematically illustrating another method for forming a multi-level layer according to one example embodiment.
• FIG. 8 is a graph illustrating the thickness of layers of material having different levels of a monomer as a function of radiation exposure according to one example embodiment.
• FIG. 9 is a graph illustrating a percent thickness loss of a material as a function of an added monomer according to one example embodiment.
• FIG. 10 is a top perspective view of a multi-level layer according to one example embodiment.
• FIG. 11 is a top perspective view of one set of portions of the multi-level layer ofFIG. 10 according to an example embodiment.
• FIG. 12 is a sectional view of a display pixel according to an example embodiment.
• FIG. 13 in a sectional view of another embodiment of a display pixel according to an example embodiment.
• FIG. 14 is a sectional view of another embodiment of a display pixel according to an example embodiment.
• FIG. 15 is a sectional view of another embodiment of a display pixel according to an example embodiment.
• FIG. 16 is a sectional view of another embodiment of a display pixel according to an example embodiment.
• FIG. 17 is a top plan view of another embodiment of the multi-level layer ofFIG. 10 according to an example embodiment.
• FIG. 18 is a sectional view of the multi-level layer ofFIG. 17 according to an example embodiment.
• FIGS. 19-22 are sectional views schematically illustrating use of the multi-level layer ofFIG. 18 to form another multi-level layer according to an example embodiment.
• FIGS. 23a-23eillustrate stages in the manufacture of a cell wall assembly having busbars and electrode structures in a predetermined alignment according to one example embodiment.
• FIG. 24 illustrates a stage in the manufacture of a cell wall assembly in accordance with another example embodiment.
• FIG. 25 is a schematic sectional view through part of a liquid crystal display device in accordance with another example embodiment.
• FIG. 26 is a schematic sectional view similar to that ofFIG. 25, through part of a device in accordance with another example embodiment.
• FIG. 27 is a similar view toFIG. 25, of another embodiment of a liquid crystal display device in accordance with another example embodiment.
DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS
• FIGS. 1-4 schematically illustrate one example of a method for forming a multi-level structure or layer40 (shown inFIG. 4). As shown byFIG. 1, alayer20 of one or more materials is initially provided. In the particular embodiment illustrated,layer20 is formed uponsubstrate22. In one embodiment,layer20 is spun uponsubstrate22. In other embodiments,layer20 may be deposited or positioned adjacent tosubstrate22 in other fashions.
• Substrate22 may constitute any structure configured to supportlayer20.Substrate22 may be electrically conductive or dielectric.Substrate22 may be transparent, partially transmissive or opaque.
• Layer20 constitutes one or more layers of one or more materials configured to exhibit a loss or reduction in thickness upon being heated. In one embodiment,layer20 is formed from materials configured to exhibit a loss or reduction in thickness based at least in part upon exposure oflayer20 to radiation. In one embodiment,layer20 includes a material configured to exhibit a loss of thickness based at least upon an extent to whichlayer20 is heated. In the particular embodiment illustrated,layer20 includes a material that exhibits a loss of thickness based upon both a degree of exposure of the material to radiation and a subsequent extent of heating of the material.
• According to one embodiment,layer20 includes a material that exhibits a loss of thickness based upon a degree of exposure to ultra-violet radiation. In one embodiment,layer20 includes a material that exhibits a loss of thickness based at least in part upon heating of the material or layer to a temperature of at least 170 degrees Celsius. In one embodiment,layer20 includes a material configured to generate various amounts of at least one cross-linking catalyst in response to being exposed to various degrees of radiation, wherein the various amounts of cross-linking catalysts generated results in different degrees of cross-linking during heating such that different percentages of materials in the layer are released, volatized or sublimed during heating.
• In one embodiment,layer20 includes a photo polymer that generates a photo acid in response to being exposed to radiation, such as ultra-violet radiation. In one embodiment,layer20 includes a negative photo resist polymer.Layer20 cross-links in response to being heated. During such heating, one or more volatile reactive molecules (VRMs) are released, volatized or sublimed from the material, resulting inlayer20 exhibiting a loss of thickness. The degree to which the VRMs are released, volatized or sublimed from the remainder oflayer20 may vary depending upon the degree to which the one or more VRMs are bound in the polymeric matrix as a result of the level or degree of cross-linking. In one embodiment,Layer20 may include a volatile reactive molecule such as a monomer. In one particular embodiment,layer20 constitutes a layer of a bisphenol-A novolac epoxy resin such as a fully epoxidized bisphenol-A/formaldehyde novolac co-polymer combined with an appropriate photo acid generator (one example is sometimes referred to as SU8). One example of SU8 is: NANO SU8-5 commercially available from MicroChem Corporation, Newton, Mass.
• FIGS. 2 and 3 illustrate selectively exposing portions oflayer20 to distinct exposure doses of radiation. As shown byFIG. 2, afirst portion24 oflayer20 is initially exposed to afirst dose26 of radiation, such as UV radiation, while a remainder oflayer20 remains unexposed to thedose26 of radiation. In the particular example illustrated, portions oflayer20 are selectively exposed todose26 of radiation using amask28.Mask28 is configured to substantially attenuate transmission ofdose26 of radiation. In one embodiment in which the radiation constitutes ultra-violet radiation,mask28 is configured to substantially attenuate ultra-violet radiation. As a result of being exposed todose26,portion24 oflayer20 generates a cross-linking catalyst such as photo acids29 (schematically illustrated by hatching). Unexposed portions oflayer20 generate little if any cross-linking catalysts as illustrated and schematically represented by the less dense hatching.
• As shown byFIG. 3,portion30 oflayer20 is exposed toexposure dose32, whileportions24 and34 are not substantially exposed todose32 of the radiation. As schematically illustrated,dose32 is relatively less thandose26. In one embodiment,dose32 may have a shorter duration. In another embodiment,dose32 may have a lesser intensity. As a result,portion30 oflayer20 generates a lesser amount of one or more cross-linking catalysts such as photo acids (as schematically represented by the lesser dense hatching). As shown inFIG. 4,portion34 generates little if any cross-linking catalysts29 (as schematically represented by the even lesser dense hatching).
• In the particular example illustrated,mask36 is used to substantially attenuate transmission ofdose32 of radiation toportions24 and34 while permitting transmission ofdose32 toportion30. In other embodiments, selective exposure oflayer20 to radiation may be performed in other manners.
• As shown byFIG. 4, after selective exposure of portions oflayer20 to radiation, such as ultra-violet radiation,layer20 is heated. As a result, cross-linkingcatalyst29 inportions24 and30 (shown inFIG. 3) cause or initiate cross-linking ofportions24 and30. As further shown byFIG. 4, a different amount ofcross-linking catalysts29 inportions24 and30 result inportions24 and30 cross-linking to different extents as schematically represented by the denser grid or matrix associated withportion24 as compared to the lesser dense grid or matrix associated withportion30. As schematically represented by the lack of a grid or matrix,portion34 has an even lesser degree or extent of cross-linking as compared toportion30.
• As further shown byFIG. 4, during heating, elements ormaterial38 are released, volatized or sublimed fromportions30 and34 to a greater extent as compared to any material that is released, volatized or sublimed fromportion24. As shown byFIG. 4, the material or elements released, volatized or sublimed fromportion34 exceeds that removed fromportion30. As a result,portion30 has a greater mass loss and reduction in thickness as compared toportion24. Likewise,portion34 has a greater percent mass loss and greater reduction in thickness as compared toportion30. This results in the formation ofdistinct levels42,44 and46 onportions24,30 and34, respectively.
• In one particular embodiment, thematerial38 released, volatized or sublimed fromportions30 and34 constitutes a VRM such as a monomer. In one embodiment in whichlayer20 includes SU8,material38 constitutes bisphenol A diglycidyl ether (BADGE monomer) in the SU8 material oflayer20. In other embodiments, other VRMs, monomers or materials may be released, volatized or sublimed from one or more ofportions24,30 and34 to formlevels42,44 and46.
• The resultingmulti-level layer40 shown inFIG. 4 includesdistinct portions24,30 and34. Each ofportions24,30 and34 has a distinct level or degree of cross-linking. Each ofportions24,30 and34 also has a distinct remaining concentration and molecular weight distribution of a VRM, such as a monomer material, that has not been removed. In particular, each ofportions24,30 and34 may have a distinct amount of VRM such as BADGE, remaining after the heating step inFIG. 4. Thedistinct levels42,44 and46 oflayer40 may serve one of several potential functions in several applications as will be described hereafter.
• FIGS. 5A and 5B illustrate alternative methods for selectively exposing portions oflayer20 to distinct exposure doses of radiation.FIG. 5A illustrates an alternative method of exposinglayer20 to radiation in lieu of the steps illustrated insteps2 and3. As shown inFIG. 5A, in lieu ofmasks28 and36 (shown and described with respect toFIGS. 2 and 3),mask56 is alternatively used to selectively expose portions oflayer20 to distinct exposure doses of radiation. In particular,mask56 includesportions58,60 and64 which substantially correspond to the desired size and shape ofportions24,30 and34 oflayer20.Portions58,60 and64 ofmask56 have distinct radiation transmissiveness. In the particular example illustrated,portions58,60 and64 are each configured to transmit different intensities of ultra-violet radiation tolayer20. In the example shown,portion58 is configured to transmit the greatest intensity of UV radiation toportion24.Portion60 is configured to transmit a lesser intensity of UV radiation toportion30.Portion64 is configured to transmit a level of ultra-violet radiation less than bothportions58 and60. In one embodiment,mask56 constitutes a grayscale mask such as a High Energy Beam Sensitive glass mask commercially available from Canyon Materials, Inc., San Diego, Calif.
• As shown byFIG. 5A,mask56 facilitates selective exposure ofportions24,30 and34 with a single period of exposure of asingle dose66 which is effectively filtered bymask56 such thatportions24,30 and34 receive distinct exposure doses68,70 and substantially no dose, respectively, (as schematically illustrated bybolts68 and70). Following the steps shown inFIG. 5A, multi-level layer40 (shown inFIG. 4) may be formed byheating layer20 ofFIG. 5A.
• FIG. 5B schematically illustrates another method of selectively exposing portions oflayer20 to distinct exposure doses of radiation.FIG. 5B schematically illustrates an alternative to the step shown inFIG. 3. In particular,FIG. 5B illustrates selectively exposing portions oflayer20 to distinct exposure doses of radiation by varying the time of exposure that different portions are exposed to radiation such as ultra-violet radiation. As discussed above inFIG. 2,portion24 oflayer20 is exposed for a first period of time toradiation dose26 while a remainder oflayer20 has minimal or no exposure. As shown byFIG. 5B, in a subsequent step,portion24 is once again exposed to dose26 of ultra-violet radiation. However,portion30 is also exposed to dose26 whileportion34 remains unexposed. In the particular example shown, amask72 is utilized to exposeportions24 and30 to radiation while substantially blocking or attenuating transmission of UV radiation toportion34. In other embodiments, a single mask may be used where the mask is moved or reconfigured. In other embodiments, thedose26 of radiation applied toportions24 and30 inFIG. 5B may alternatively have a distinct intensity or duration as compared todose26 that was applied in the step illustrated inFIG. 2.
• Becauseportion24 is subjected to radiation for a longer total period of time as compared toportions30 and34, a larger amount of cross-linking catalysts are generated inportion24. Likewise, becauseportion30 is exposed to a longer duration as compared toportion34, a greater amount of cross-linking catalysts are generated inportion30 as compared toportion34. As discussed above with respect toFIG. 4, the different levels of cross-linking catalysts generated inportions24,30 and34 result in distinct degrees of thickness loss inportions24,30 and34 to formlevels42,44 and46 in the finishedmulti-level layer40 shown inFIG. 4.
• Overall, the process or method shown inFIGS. 1-4,5A and5B facilitates fabrication of a single layer of material having multiple distinct levels with fewer individual processing steps and at a lower cost. In particular, the method illustrated inFIGS. 1-4,5A and5B forms a multi-level layer40 (shown inFIG. 4) which utilizes a single coating process (FIG. 1). Because thickness variations are achieved based upon different levels of cross-linking and by volatizing materials fromlayer20, developing processes, etching processes and stripping processes may be omitted. In addition, the described process utilizes minimal consumables and may result in minimal process waste disposal. Using grayscale masks, such asmask56 shown inFIG. 5A, highly repeatable analog changes in thickness may be achieved. In sum, the general method described inFIGS. 1-4,5A and5B facilitates low-cost fabrication of multi-level layers or structures.
• FIG. 6 graphically illustrates thickness loss of a layer of unexposed SU8 as a function of time and temperature at which the layer was heated. As shown byFIG. 6, materials within the SU8 layer, such as a monomer BADGE, begin volatizing, subliming or being released from the layer at a temperature of about 130 degrees. The degree to which such materials are released from the layer to produce changes in thickness of the layer greatly increases when the layer is heated at a temperature of at least about 170 degrees. Heating the unexposed layer of SU8 at 250 degrees for 15 minutes yielded the greatest percent thickness loss of the layer.
• FIG. 7 schematically illustrates another method for formingmulti-level layer40 shown inFIG. 4. As shown inFIG. 7, in lieu of or in addition to exposingportions24,30 and34 to distinct doses of ultra-violet radiation to formdistinct levels42,44 and46 of layer40 (shown inFIG. 4),portions24,30 and34 may be subjected to different amounts of heating by varying one or both of the time and temperature at whichportions24,30 and34 are heated.
• In one embodiment,portions24,30 and34 may be subjected to different levels of heating using aheating device80 which includes anenergy source82 and one or more structures84 (schematically illustrated) for applying different levels of heat or different levels of energy as schematically represented byarrows86,88 and90 toportions24,30 and34, respectively. In one embodiment,energy source82 may emit a substantially uniform level of heat acrosslayer20 whilestructure84 constitutes a masking device that thermally insulatesportions24,30 and34 to different extents from heat provided by theenergy source82. In another embodiment,energy source82 may emit distinct levels of heat in distinct zones separated by heat shields and aligned withportions24,30 and34. In still another embodiment,heating device80 may constitute a laser configured to selectively apply different levels of energy toportions24,30 and34 by varying the intensity of the laser or the duration at which the laser is applied toportions24,30 and34. In one embodiment, the heat may be applied tolayer20 withoutlayer20 being exposed to ultra-violet radiation. In other embodiments, such selective heating oflayer20 may be performed afterlayer20 has been exposed to ultra-violet radiation. In embodiments in which different levels of heat or energy are used to form different levels, an optional final two steps of exposing oflayer20 to an unmasked dose of radiation followed by heating oflayer20 to bind any remaining monomer into place can be performed to substantially eliminate any further monomer evaporation over time.
• As shown inFIG. 6 above, subjecting unexposed SU8 to a temperature of 250 degrees for about 15 minutes resulted in a 12 percent loss of overall thickness of the SU8 layer. In particular applications, it may be beneficial to achieve greater percent thickness losses.
• FIG. 8 is a graph illustrating various thicknesses of layers of SU8 having different amounts of added monomer, such as BADGE, as a result of being exposed to UV radiation to different extents then being heated at a temperature of at least 250 degrees C. for 2 minutes. In the example shown inFIG. 8, the layers are exposed to UV light having a wavelength of 365 nanometers for different periods of time given in milliseconds (ms). The intensity of the light is such that energy is applied at a rate of 0.5 millijoules per centimeter squared per millisecond. As shown byFIG. 8, for a fixed amount of added monomer, higher exposure levels of SU8 to ultra-violet radiation result in thicker final films after being heated at a temperature of 250 C for at least 2 minutes. In addition, as the amount of BADGE, as a percentage of total solids of the SU8, is increased, the percent difference between the thickness of two different areas subjected to fixed differences of exposure to ultra-violet radiation and subsequently heated at the same temperature for the same duration also increases. In particular, it has been found that the percent thickness loss of SU8 after being exposed and heated may be defined as follows:
• 
  L=Re^−kd/(B+R)*100 where:
• • L=percent loss of thickness;
  • B=a predetermined floor constant;
  • R=a range constant;
  • k=a constant; and
  • d =exposure dose
• FIG. 9 graphically illustrates percentage thickness loss of a layer of unexposed SU8 as a function of addition of a monomer such as BADGE above the level of BADGE contained in commercially available SU8. The level of BADGE contained in commercially available SU8 is estimated to be between approximately 15-20 percent by mass. In the particular examples illustrated, the layer of SU8 experienced an approximately 18 percent loss of thickness upon being heated as compared to the same heating of the same SU8 that had been exposed to high doses of ultra-violet radiation, where high is defined here as at least about 3000 ms. The18 percent thickness loss exhibited by the unexposed SU8 ofFIG. 8 as compared to the approximately12 percent thickness loss of the unexposed SU8 ofFIG. 6 is believed to be the result of the layer ofFIG. 9 being thinner, facilitating greater percentage volatization of BADGE in the layer.
• As further shown byFIG. 9, as the percent total solids of BADGE is added to the SU8 layer, the relative percentage thickness loss from portions of the layer that have been exposed to approximately 3,000 ms of ultra-violet radiation as compared to other portions of the same layer of SU8 that remain unexposed increases. As shown byFIG. 9, the rate at which the percent thickness loss increases is a linear function of the percent of total solids of BADGE added to the SU8 material. As shown byFIG. 9, up to over 70 percent thickness loss may be achieved with the addition of BADGE in the amount of approximately 60 percent of the total solids (excluding solvents) of the SU8 layer.
• Thus, as shown byFIG. 9, by adding BADGE or other monomers to the negative resist polymer, such as SU8, percent thickness losses may be increased to enhance height differences between levels of a multi-level layer such aslayer40 shown inFIG. 4. In other embodiments, in lieu of adding a VRM, such as BADGE to a commercially available photo polymer such as SU8, materials having appropriate concentrations of VRMs, such as monomers such as BADGE, may be directly formed or synthesized to provide a volatile polymer that has varying degrees of volatization upon being heated to provide distinct thicknesses or levels.
• FIGS. 10 and 11 illustratemulti-level layer140, another embodiment ofmulti-level layer40 shown inFIG. 4. As shown byFIG. 10,layer140 includes a repeating pattern of groupings or sets141 of multipledistinct portions124,128,130 and134. As shown byFIG. 11 which illustrates asingle set141,portions124,128,130 and134 have distinct thicknesses which results in each of such portions having distinct levels. In particular,portions124,128,130 and134 includedistinct levels142,144,146 and148, respectively. In the example illustrated, eachportion124,128,130 and134 has a specific amount of a cross-linking agent, wherein eachportion124,128 to130 and134 has a distinct thickness for the specified amount of the cross-linking agent. Each ofportions124,128,130 and134 also has a distinct remaining concentration and molecular weight distribution of a VRM such as BADGE.
• Portions124,128,130 and134 of each set141 oflayer140 are formed according to one of the methods illustrated and described with respect toFIGS. 1-4,5A,5B or7. As a result,layer140 is formed utilizing a single coating process (FIG. 1). Because such thickness variations are achieved based on different levels of cross-linking and volatizing materials fromlayer140, developing processes, etching processes and stripping processes may be omitted. In addition,layer140 may be formed from a process that utilizes minimal consumables and may result in minimal process waste disposal. Utilizing grayscale masks, such asmask56 shown inFIG. 5A, highly repeatable analog changes in thickness may be achieved. In addition, gradual sloped or ramped transitions151 (shown inFIG. 10) between one or more ofportions124,128,130 and134 may be formed. In particular embodiments, one or more ofportions124,128,130 and134 may themselves be at least substantially ramped, sloped or tapered as shown by rampedportion130′ or151 (shown inFIG. 10).
• In the particular example illustrated,layer140 includes a photo polymer that generates a photo acid in response to being exposed to radiation, such as ultra-violet radiation. In one embodiment,layer140 includes a negative photoresist polymer.Layer140 cross-links in response to being heated. During such heating, one or more volatile reactive molecules are released, volatizing or sublimed from the material, resulting inlayer140 further exhibiting in loss of thickness. The degree to which the VRMs are released, volatized or sublimed from the remainder oflayer140 may vary depending upon the degree to which the one or more VRMs are bound in the polymer matrix as a result of the level or degree of cross-linking. In one embodiment,layer140 may include a volatile reactive molecule such as a monomer. In one embodiment,layer140 constitutes a layer of a bisphenol-A novolac epoxy resin such as a fully epoxidized bisphenol-A/formaldehyde novolac co-polymer combined with an appropriate photo acid generator (one example of which is sometimes referred to as SU8).
• In the example illustrated,levels142,144,146 and148 are formed by applying distinct doses of ultraviolet radiation to each ofportions124,128,130 and134, respectively, prior to the applying heat tolayer140. In one example embodiment, portioning134 is exposed to an ultraviolet radiation dose of about 200 mJ/cm2.Portion130 is exposed to an ultraviolet radiation dose of about 250 mJ/cm2 which results inlevel146, at its center, extending at a height of about 71 nm abovelevel148 ofportion134.Portion128 is exposed to an ultraviolet radiation dose of about 350 mJ/cm2 which results inlevel144, at its center, extending at a height of about 194 nm abovelevel148 ofportion134.Portion124 is exposed to an ultraviolet radiation dose of about 550 mJ/cm²which results inlevel142 extending at a height, at its center, of about 315 nm abovelevel148 ofportion134. In another embodiment,portions124,128,130 and134 are exposed to appropriate levels of ultraviolet radiation such thatlevels142,144,146 and148 have height variations of at least 100 nm between each level. In yet other embodiments,portions124,128,130 and134 may be exposed to other levels or doses of ultraviolet radiation such thatlevels142,144,146 and148 have other relative heights.
• In further embodiments, an optional post expose bake then develop step can be inserted immediately after exposure to substantially remove portions that have been completely masked out and therefore had no exposure. Subsequently, all portions can then be heated to define the height variation that have been previously described.
• FIGS. 12-16 schematically illustrate various embodiments includingmulti-level layer140. In particular,FIGS. 12-16 are sectional views of individual display pixels including one set141 ofmultilevel layer140 taken alongline12—12 ofFIG. 11.FIG. 12 illustrates apixel199 of adisplay200. Althoughlayer140 is illustrated as including asingle set141 ofportions124,128,130 and134,display200 includes alayer140 having a repeating pattern ofsuch sets141 as shown inFIG. 10. In other embodiments,display200 may alternatively include alayer140 having a single set ofportions124,128,130 and148. In yet other embodiments, each set141 may alternatively include greater or fewer than four portions. In addition tomultilevel layer140,display200 further includesfront substrate202,electrode204, alignment layers206,208,substrate210,electrode212,active layer220,voltage driver222 andcontroller224.
• Substrate202 comprises one or more layers of one or more materials serving as a base or foundation upon whichelectrode204 andalignment layer206 are formed.Front substrate202 is formed from an optically transparent and clear dielectric material. In one embodiment,front substrate202 may be formed from an optically clear and flexible dielectric material that is birefringence free such as polyethersulfone (PES). In other embodiments, that omit a polarizer, transparent films or materials having birefringence such as polyethyleneterephthalate (PET) may be employed. In other embodiments,front substrate202 may be formed from other transparent dielectric materials that may be inflexible such as glass.
• Electrode204 constitutes a layer of transparent or translucent electrically conductive material formed uponsubstrate202.Electrode204 is configured to be charged to cooperate withelectrode212 to create an electric field acrossactive layer220. In one embodiment,electrode204 may constitute a transparent conductor such as indium tin oxide (ITO) or a conductive transparent polymer such as Polyethylenedioxythiophene polystyrenesulfonate: (PEDOT:PSS) which is commercially available from HC Starck. In other embodiments the transparent conductive coating may comprise other materials such as carbon nanotubes, zinc oxide, tin oxide, zinc tin oxide, copper indium oxide, strontium copper oxide, cadmium oxide and thin layers of metals such as Al, Pt, Ag, Au, Cu. In other embodiments,electrode204 may be formed from other translucent or transparent electrically conductive materials.
• Alignment layer206 comprises a layer of material uponelectrode204 and in contact withactive layer220. Similarly,alignment layer208 comprises a layer ofmaterial overlying layer140 and in contact withactive layer220. Alignment layers206 and208 cooperate to align liquid crystals ofactive layer220. For example, in those embodiments in whichactive layer220 includes twisted nematic liquid crystals, layers206 and208 cooperate to align such liquid crystals in an appropriate orientation. In one embodiment,layer206 may comprise a rubbed polyimide having parallel microscopic grooves in a first direction whilelayer208 comprises a rubbed polyimide having parallel microscopic grooves in a second direction orthogonal to the first direction. In other embodiments,layers206 and208 may have other configurations for aligning liquid crystals ofactive layer220. In yet another embodiment, the alignment layer may be composed of microstructures, such as posts or grooves. In particular embodiments,layers206 and208 may be omitted where alignment of crystals ofactive layer220 may be omitted. For example, alignment layers206 and208 may be omitted in those embodiments in whichactive layer220 comprises polymer dispersed liquid crystal or the active layer is composed of materials other than liquid crystals displays that requires polarizers or any active layer materials which effect an optical response.
• Substrate210 comprises one or more layers of one or more materials configured to supportelectrode212 andlayer140. In embodiments wheredisplay200 is a transmissive or backlit display,substrate210 is formed from one or more optically clear or transparent materials. In one embodiment,substrate210 may be formed from an optically clear and flexible dielectric material that is birefringence free such as polyethersulfone (PES). In other embodiments, that omit a polarizer, transparent films or materials having birefringence such as polyethyleneterephthalate (PET) may be employed. In other embodiments,substrate210 may be formed from other transparent dielectric materials that may be inflexible such as glass. In another embodiment wheredisplay200 is a front lit display,substrate210 may be formed from one or more rigid opaque dielectric materials.
• Electrode212 is similar toelectrode204.Electrode212 is configured to be charged to cooperate withelectrode204 to create an electric field acrossactive layer220. In embodiments in which display200 comprises a backlit display,electrode212 is formed from one or more optically clear or transparent electrically conductive materials such as ITO or PEDOT:PSS. In other embodiments the transparent conductive coating may comprise other materials such as carbon nanotubes, zinc oxide, tin oxide, zinc tin oxide, copper indium oxide, strontium copper oxide, cadmium oxide and thin layers of metals such as Al, Pt, Ag, Au, Cu. In embodiments wheredisplay200 is a front lit display,electrode212 may be formed from one or more transparent electrically conductive materials or opaque electrically conductive materials. In such an embodiment,electrode212 may be formed from an electrically conductive material that is also highly reflective.
• Active layer220 comprises a layer of any electro-optically responsive material configured withalignment layers206,208 to change its optical behaviour in response to an applied electric field. In one embodiment, the retardation of polarised light is modified such that when viewed through a suitably aligned polarising film, the display pixel can modulate the intensity of transmitted or reflected light. In other embodiments,active layer220 may contain re-orientable dichroic dye molecules or pigments such that transmitted or reflected light is modulated without the need for external polarizing elements. In further embodiments,active layer220 may modulate the scattering of incident light by means of polymer dispersed liquid crystals. In yet further embodiments,active layer220 may modulate the spectral content (i.e. color) of incident light. In still other embodiments,layer220 may comprise other presently developed or future developed materials configured to selectively block, absorb or attenuate light
• In one embodiment the electro-optical effect or state oflayer220 has a optical threshold, and in a further example embodiment, the electro-optical effect oflayer220 has state memory (i.e. bistability) with a distinct threshold field level. By this means, when a voltage is applied betweenelectrodes204,212, areas of the pixel which receive a field strength higher than the memory threshold will change state, whereas areas which receive a lower field will not. By design of the areas and thickness of thestructures140, spatial greytone may be generated. This is particularly beneficial to electro-optical effects or states which have a distinct optical threshold such as, but not limted to, ferroelectric liquid crystal, bistable nematic liquid crystal, cholesteric texture liquid crystal, viologen based electro-chromic, MEMS or micro-fluidic devices.
• Active layer220 extends betweenelectrodes204 and212.Active layer220 includesregions234,238,240 and244.Regions234,238,240 and244 extend opposite toportions124,128,130 and134 oflayer140, respectively. Becauselayer140 is a dielectric material and becauseportions124,128,130 and134 have differing thicknesses, regions234-244 experience different electric fields having different strengths even though a common voltage is created betweenelectrodes204 and212. As a result, regions234-244 will change between different electro-optical effects including but not limited to different light attenuating states or different wavelength absorbing states at different times or in response to different voltages created betweenelectrodes204 and212.
• For example, becauseportion134 has the smallest thickness,region244 experiences the strongest electrical field for a given voltage betweenelectrodes204 and212. As a result,region244 will change between different electro-optical effects or states at a lower voltage betweenelectrodes204,212 as compared to regions234-240. Similarly,region240 will change at a lower voltage as compared toregions238 and234 andregion238 will change at a lower voltage as compared toregion234. Thus, the multiple distinct thicknesses oflayer140 enable distinct regions ofactive layer220 and the associated pixel ofdisplay200 to be selectively actuated between different electro-optical states based upon the voltage applied acrosselectrodes204 and212 by bothdriver222 andcontroller224. The selective actuation of regions234-244 may be achieved without electrical switching elements provided for each of regions234-244, reducing the cost and complexity ofdisplay200.
• Voltage driver222 comprises one or more devices or structures configured to selectively apply voltages across theelectrodes204 and212 to control an electric field created acrossactive layer220. In one embodiment,driver222 may comprise one or more voltage sources and one or more electrical switching elements, such as transistors, metal-insulator-metal devices, diodes and the like. Such electrical switching elements may be arranged as part of an active-matrix control, wherein the electrical switching elements are proximate each of the pixels or sets141 or a passive control, wherein the electrical switching elements are grouped together distant the pixels or sets141.
• Controller224 comprises a processing unit configured to generate control signals based upon desired images to be displayed bydisplay200, whereindriver222, in response to such control signals, creates appropriate voltages betweenelectrodes204 and212 and acrossactive layer220. For purposes of this application, the term “processing unit” shall mean a presently developed or future developed processing unit that executes sequences of instructions contained in a memory. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described.Controller224 is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit.
• In operation,controller224 generates control signals based upon an image to be displayed bydisplay200. In response to such control signals,driver222 establishes a desired voltage acrosselectrodes204 and212 to selectively control how many ofregions234,238,240 and244 of one ormore sets141 are actuated between different light attenuating or absorbing states. For example, for a particular pixel ofdisplay200 having aparticular set141 of portions oflayer140, a first voltage may be applied acrosselectrodes204 and212 to actuateregion244 whileregions234,238 and240 remain unactuated. To additionally actuateregion240 ofactive layer220, a larger voltage may be applied acrosselectrodes204 and212. Likewise, even larger voltages may be applied acrosselectrodes204 and212 to additionally selectively actuateregions238 and234.
• FIG. 13 schematically illustrates asingle pixel299 ofdisplay300, another embodiment ofdisplay200.Pixel299 is similar topixel199 except thatpixel299 includessubstrate302, adhesive303,electrode304 andactive layer320 in lieu ofsubstrate202,electrode204 andactive layer220, respectively, omits alignment layers206,208 and additionally includeslight altering layer314. Those remaining elements ofpixel299 and display300 which correspond topixel199 anddisplay200 are numbered similarly.
• Substrate302 is similar tosubstrate202 except thatsubstrate302 supportslayer140 andelectrode304 which are joined to substrate byadhesive layer303. Likesubstrate202,substrate302 is formed from one or more layers of one or more optically clear or transparent dielectric materials. In one embodiment,substrate302 may comprise an optically clear and flexible dielectric material that is birefringence free such as polyethersulfone (PES). In other embodiments, that omit a polarizer, transparent films or materials having birefringence such as polyethyleneterephthalate (PET) may be employed. In other embodiments,substrate302 may be formed from other transparent dielectric materials that may be inflexible such as glass.
• Adhesive layer303 comprises a transparent adhesive. In one embodiment, the adhesive may comprise a UV-curable material such as NOA81 (Norland Optical Products), but alternatively may be thermal or moisture cured.
• Electrode304 is similar toelectrode204 except thatelectrode304 is stepped as it extends overportions124,128,130 and134 oflayer140. Likeelectrode204,electrode304 is formed from an optically clear or transparent electrically conductive material. In one embodiment,electrode304 may comprise a transparent conductor such as ITO or PEDOT:PSS. In other embodiments the transparent conductive coating may comprise other materials such as carbon nanotubes, zinc oxide, tin oxide, zinc tin oxide, copper indium oxide, strontium copper oxide, cadmium oxide and thin layers of metals such as Al, Pt, Ag, Au, Cu. In other embodiments,electrode304 may be formed from other translucent or transparent electrically conductive materials.
• Active layer320 comprises a layer of optical charge responsive material configured to change from a transparent state, allowing light to pass throughactive layer320, to a generally opaque state in which light is absorbed or otherwise attenuated bylayer320 in response to changes in an applied voltage or charge. In the particular example illustrated,active layer320 comprises a polymer-dispersed liquid crystal, permitting alignment layers206,208 (shown inFIG. 12) to be omitted. In other embodiments,active layer320 may comprise other optical charge responsive materials. For example,active layer320 may comprise a nematic liquid crystal, whereindisplay300 additionally includes alignment layers206 and208 (shown inFIG. 12). Likelayer220,layer320 includesregions234,238,240 and244 generally opposite toportions124,128,130 and134 oflayer140. As a result of the different thicknesses ofportions124,128,130 and134spacing electrode304 fromactive layer320,regions234,238,240 and244 actuate or change between different light attenuating states in response to different applied voltages created betweenelectrodes304 and212.
• Light altering layer314 comprises one or more layers of one or more materials configured to alter or change light prior to or after the transition of light acrossactive layer320. In one embodiment in which display300 comprises a backlit display,layer314 may comprise a light filtering layer configured to filter selected wavelengths of light. In such an embodiment,layer314 may includedistinct portions344,348,350 and354 opposite toregions234,238,240 and244, respectively. Each portion344-354 may be configured to filter a different range of wavelengths of light. For example,region344 may filter red light,348 may filter blue light,region350 may filter green light andregion354 may block or reflect all light or filter other wavelengths of light. In other embodiments in which displays300 comprises a front lit display,layer314 may be configured to reflect selected wavelengths of light or may be configured to reflect substantially all wavelengths of light. In one embodiment, portions344-354 oflayer314 may each be configured to reflect different ranges of wavelengths of light. In yet other embodiments,layer314 may be configured to filter or reflect a single color of light, wherein adjacent pixels havelayers314 that filter or reflect other colors of light. For example, in one embodiment,layer314 may filter (in the case of a backlit display) or reflect (in the case of a front lit display) red light. Adjacent pixels may havelayers314 that filter or reflect green light or blue light. In some embodiments, portions344-354 may alternatively be configured to reflect the same wavelengths of light. For example, in another embodiment, substantially all oflayer314 may be white. In yet other embodiments,layer314 may be omitted.
• FIG. 14 schematically illustrates onepixel399 ofdisplay400, another embodiment ofdisplay200.Display400 is similar to display200 (shown inFIG. 12) except thatdisplay400 omits alignment layers206,208, includesactive layer420 in lieu ofactive layer220 and additionally includeslayer440 and light altering layer314 (described above with respect toFIG. 13). Those remaining elements ofdisplay400 which correspond to elements ofdisplay200 are numbered similarly.Active layer420 is similar toactive layer320 of display300 (shown and described with respect toFIG. 13). In the example illustrated,active layer420 comprises a polymer-dispersed liquid crystal, permitting alignment layers206 and208 to be omitted. In other embodiments,active layer420 may comprise other materials configured to change between different light attenuating or light absorbing states in response to different electric fields. For example, in other embodiments,active layer420 may comprise other liquid crystals. In those environments in whichactive layer420 includes liquid crystals that should be aligned, such as twisted nematic crystals,display400 may additionally includealignment layers206,208 as described above with respect toFIG. 12.
• Active layer420 includesregions444,448,450 and454.Regions444,448,450 and454 experience different electrical fields as a result oflayers140 and440. Consequently,regions444,448,450 and454 change between different light attenuating or light absorbing states at different times in response to different voltages applied acrosselectrodes204 and212.
• Layer440 is substantially similar tolayer140.Layer440 is supported bysubstrate202 and extends betweenelectrode204 andactive layer420.Layer440 is formed according to one of the methods described above with respect toFIGS. 1-4,5A,5B orFIG. 7. As shown byFIG. 14,layer440 includesdistinct portions464,468,470 and474 which have different thicknesses and which extend opposite toportions124,128,130 and134 oflayer140, respectively.
• Likelayer140,layer440 controls the strength of the electrical field experienced byactive layer420 even though a common voltage is created betweenelectrodes204 and212. As a result, regions444-454 will change between different light attenuating states or wavelength absorbing states at different times or in response to different voltages created betweenelectrodes204 and212. For example, becauseportion474 has the smallest thickness,region454 experiences the strongest electrical field for a given voltage betweenelectrodes204 and212. As a result,region454 will change between different light attenuating or absorbing states at a lower voltage betweenelectrodes204,212 as compared to regions444-450. Similarly,region450 will change at a lower voltage as compared toregions444 and448 andregion448 will change at a lower voltage as compared toregion444. Thus, the multiple distinct thicknesses oflayer440 enable distinct regions ofactive layer420 and the associated pixel ofdisplay400 to be selectively actuated between different light absorbing or light attenuating states based upon the voltage applied acrosselectrodes204 and212 by bothdriver222 andcontroller224. Becausedisplay400 includes bothlayers140 and440, greater electrical field variations betweenelectrodes204 and212 may be achieved, permitting selective actuation of regions444-454 with less costly and less precise voltage control. In addition, the greater electric field variations facilitate the addition of more selectively actuatable regions ofactive layer420. The selective actuation of regions444-454 may be achieved without electrical switching elements provided for each of regions444-454, reducing the cost and complexity ofdisplay400.
• FIG. 15 schematically illustrates anindividual pixel499 ofdisplay500, another embodiment ofdisplay200.Display500 is substantially similar to display400 except thatdisplay500 includessubstrate510,adhesive layer511,electrode512 andmulti-level layer540 in lieu ofsubstrate210,electrode212 andlayer140, respectively. Those remaining elements ofdisplay500 which correspond to elements ofdisplay400 are numbered similarly. Likesubstrate210,substrate510 is formed from one or more layers of one or more optically clear or transparent dielectric materials. In one embodiment,substrate510 may be formed from an optically clear and flexible dielectric material that is birefringence free such as polyethersulfone (PES). In other embodiments, that omit a polarizer, transparent films or materials having birefringence such as polyethyleneterephthalate (PET) may be employed. In other embodiments,substrate510 may be formed from other transparent dielectric materials that may be inflexible such as glass. In yet other embodiments in which display500 is a front-lit display,substrate510 may be formed from an opaque or reflective dielectric material.
• Adhesive layer511 connects and spaces electrode512 andsubstrate510.Adhesive layer511 comprises a transparent adhesive. In one embodiment, the adhesive may comprise a UV-curable material such as NOA81 (Norland Optical Products), but alternatively may be thermal or moisture cured.
• Electrode512 is similar toelectrode212 except thatelectrode512 is stepped as it extends overportions124,128,130 and134 oflayer140. Likeelectrode212,electrode512 is formed from an optically clear or transparent a likely conductive material. In one embodiment,electrode512 may constitute a transparent conductor such as ITO or PEDOT:PSS. In other embodiments the transparent conductive coating may comprise other materials such as carbon nanotubes, zinc oxide, tin oxide, zinc tin oxide, copper indium oxide, strontium copper oxide, cadmium oxide and thin layers of metals such as Al, Pt, Ag, Au, Cu. In other embodiments,electrode512 may be formed from other translucent or transparent electrically conductive materials. In still other embodiments in which display500 comprises a front-lit display,electrode512 may be formed from reflective or opaque electrically conductive materials.
• Layer540 is substantially identical to layer140 except thatlayer540 is inverted.Layer540 includesportions124,128,130 and134 which extend opposite toportions464,468,470 and474 oflayer440. The differing thicknesses ofportions124,128,130 and134 result inactive layer420 experiencing different electric field strengths for a single given voltage betweenelectrode204 andelectrode512. As a result, regions444-454 ofactive layer420 may be selectively actuated between states by controlling the voltage acrosselectrodes204 and512.
• FIG. 16 schematically illustratespixel599 ofdisplay600, another embodiment of display200 (shown and described with respect toFIG. 12).Display600 is substantially similar to display500 ofFIG. 15 except thatdisplay600 includessubstrate602,adhesive layer603,electrode604 andmulti-level layer640 in lieu ofsubstrate202,electrode204 andlayer440, respectively. Those remaining elements ofdisplay600 which correspond to elements ofdisplay500 are numbered similarly. Likesubstrate202,substrate602 is formed from one or more layers of one or more optically clear or transparent dielectric materials. In one embodiment,substrate602 may be formed from an optically clear and flexible dielectric material that is birefringence free such as polyethersulfone (PES). In other embodiments, that omit a polarizer, transparent films or materials having birefringence such as polyethyleneterephthalate (PET) may be employed. In other embodiments,substrate602 may be formed from other transparent dielectric materials that may be inflexible such as glass.
• Adhesive layer603 connects and spaces electrode604 andsubstrate602.Adhesive layer603 comprises a transparent adhesive. In one embodiment, the adhesive may comprise a UV-curable material such as NOA81 (Norland Optical Products), but alternatively may be thermal or moisture cured.
• Electrode604 is similar toelectrode204 except thatelectrode604 is stepped as it extends overportions464,468,470 and474 oflayer640. Likeelectrode204,electrode604 is formed from an optically clear or transparent a likely conductive material. In one embodiment,electrode604 may constitute a transparent conductor such as ITO or PEDOT:PSS. In other embodiments the transparent conductive coating may comprise other materials such as zinc oxide, tin oxide, zinc tin oxide, copper indium oxide, strontium copper oxide, cadmium oxide, carbon nanotubes and thin layers of metals such as Al, Pt, Ag, Au, Cu. In other embodiments,electrode604 may be formed from other translucent or transparent electrically conductive materials
• Layer640 is substantially identical to layer440 except thatlayer640 is inverted.Layer640 includesportions464,468,470 and474 which extend opposite toportions124,128,130 and134 oflayer540. The differing thicknesses ofportions464,468,470 and474 result inactive layer420 experiencing different electric field strengths for a single given voltage betweenelectrode604 andelectrode512. As a result, regions444-454 ofactive layer420 may be selectively actuated between states by controlling the voltage acrosselectrodes604 and512. In addition, becauselayer420 has a substantially uniform thickness over the area of all thepixies600, improved performance and manufacturing efficiencies may result.
• FIGS. 17 and 18 illustratemulti-level layer740, another embodiment ofmulti-level layer140.Multi-level layer740 is similar tolayer140 except thatlayer140 includes a repeating pattern ofsets741 ofportions724,728,730 and734.Portion724,728,730 and734 are similar toportions124,128,130 and134 oflayer140, respectively, except thatportion734 comprises the floor oflayer740 extending betweenadjacent sets741, that portions of724,728 and730 are stacked upon one another so as to extend outwardly beyond one another and thatportions724,728 and730 are circular.
• Likeportions124,128 and130 and134,portion724,724,730 and734 have distinct thicknesses. In particular, eachportion724,728,730 and734 has a specific amount of a cross-linking agent, wherein eachportion724,728,730 and734 has a distinct thickness for the specified amount of the cross-linking agent. Each ofportions724,728,730 and734 also has a distinct remaining concentration and molecular weight distribution of a VRM such as BADGE.
• Portions724,728,730 and734 of each set741 oflayer740 are formed according to one of the methods illustrated and described with respect toFIGS. 1-4,5A,5B or7. As a result,layer740 is formed utilizing a single coating process (FIG. 1). Because such thickness variations are achieved based on different levels of cross-linking and volatizing materials fromlayer740, developing processes, etching processes and stripping processes may be omitted.
• Althoughportions724,728,730 and734 are illustrated as being circular, in other embodiments,portions724,728 and730 may alternatively be square, rectangle or, triangular or have other shapes. Althoughportions724,728 and730 are illustrated as having a common shape, in other embodiments, such portions may have differing shapes from one another. Although each set741 is illustrated as having four distinct portions or levels, in other embodiments, each set741 may include greater or fewer number of such portions.
• FIGS. 19-22 illustrate the formation of a multi-level layer840 (shown inFIG. 22) using multi-level layer740 (shown inFIG. 18). As shown byFIG. 19, afterlayer740 is formed, alayer760 of polymeric material is formed overlayer740.Layer760 may comprise a UV, thermal or moisture curable material. In other embodiments,layer760 may comprise one or more other polymeric materials.
• As shown byFIG. 20, upon solidification or curing oflayer760,layer760 is separated fromlayer740. As shown byFIG. 21, alayer764 of dielectric material is formed upon adielectric substrate766. Thereafter,layer760 is imprinted or embossed againstlayer764 to formmulti-level layer840 uponsubstrate766. As shown byFIG. 22, upon solidification or curing of the imprintedlayer764, layer760 (shown inFIG. 21) is separated fromlayer764 to producemulti-level layer840.Multi-level layer840 may be used in lieu oflayers140,440 and540 indisplays200,300,400 and500 as described above.Layer760 may also be used for forming additionalmultilevel layers840. In such an embodiment,layer764 andmultilevel layer840 may be formed from various dielectric materials.
• According to one embodiment,layer764 comprises a layer of a bisphenol-A novolac epoxy resin such as a fully epoxidized bisphenol-A/formaldehyde novolac co-polymer combined with an appropriate photo acid generator (an example of which is sometimes referred to as SU8). In such an embodiment,layer760 is formed from one or more UV radiation transmitting materials, whereinlayer764, while imprinted bylayer760, is exposed to ultraviolet radiation passing throughlayer760. In particular embodiments,layer764 may be provided with appropriate levels of BADGE anddistinct portions824,828,830 and834 oflayer764 being imprinted bylayer760 may be exposed to different doses of ultraviolet radiation throughlayer760 such that portions824-834 undergo different degrees of cross-linking and underground different degrees of volatization upon being subsequently heated so as to enlarge thickness differences betweenportions824,828,830 and834 of the resultingmultilevel layer840.
• FIGS. 23a-23eillustrate a method for forming apixel999 of a display1000 (shown inFIG. 25). Atransfer carrier901 is shown inFIG. 23a.Thecarrier901 comprises abase film902 on which is coated a planarconductive layer903. Thecarrier901 may be rigid or flexible. In this example, thebase film902 comprises 150 μm thick PET and theconductive layer903 is copper metal of about 1 μm thickness. In this example, thecopper layer903 is optically flat and has been passivated by immersion in 0.1 N potassium dichromate solution for 5 minutes, rinsed with deionised water and air-dried. Alternatively, the base film may itself be a conductor.
• Multi-level layer740 (described above) is formed on the surface of the conductive layer903 Atrench906 is formed inlayer740. If necessary, thetrench906 is plasma-etched to remove polymer from the bottom of thetrench906. Metal, in this example nickel, is then electroplated into thetrench906 to form a busbar908 (FIG. 23b). In one embodiment, theconductor903 forms the cathode of an electrolytic cell with a nickel anode and a nickel sulphamate-based electrolyte. Plating may be carried out with DC, with pulsed or biased AC current used to fill in thetrenches906 completely. Other existing electroplating or electroless plating techniques may be employed. Suitable metals include nickel, copper and gold. Thebusbars908 are linear structures which will run across the length or width of the display substrate (cell wall) to which they are transferred. They are typically about 100 μm apart and up to many metres in length. Thebusbars908 are about 5×5 μm is cross-section and have a low resistance that in use will apply an applied voltage evenly across the device. The metal of thebusbar908 is opaque but it is small enough not to reduce the aperture to a large extent.
• To form electrode structures, atransparent conductor910 is deposited onto themulti-level layer740 andbusbars908, as illustrated inFIG. 23c.Theconductor910 may comprise indium oxide, tin oxide, indium tin oxide (ITO) or the like, but is preferably an organic conductor such as PEDOT:PSS (HC Starck Baytron P), which may be applied by a printing technique such as inkjet printing. The transparent conductor is then selectively etched or bleached to providetransparent electrodes910. Standard photolithographic techniques can be used to prevent the conductor contacting more than onebusbar908. In the preferred embodiment, PEDOT:PSS is selectively bleached by UV light to form the electrode structures. Alternatively, standard photoresists and etching or chemical deactivation may be employed.
• It will be understood that, for simplicity, only a singlemulti-level layer740,busbar908 andelectrode track910 are shown. A plurality of similar dielectric structures, busbars and electrode structures will be formed, eachelectrode structure910 typically comprising one of a series of parallel row or column electrodes.
• After forming theelectrode structures910, the resulting structure is treated with atransparent adhesive914 and thefinal display substrate912 is laminated and the adhesive914 is cured (FIG. 23d). In a preferred embodiment the adhesive914 is a UV-curable material such as NOA81 (Norland Optical Products) but may be thermal- or moisture-cured. Thedisplay substrate912 is preferably a plastics material, for example, ZF-16 by Zeon Chemical, PEN (DuPont Teijin Teonex Q65), PES (Sumitomo Bakelite) or polyArylate (Ferrania SpA—Arylite), but could comprise glass, preferably a UV-translucent glass.
• The adhesions in the assembly shown inFIG. 23dare tuned such that when thetransfer carrier901 is peeled off, the adhesion breaks at the surface of the conductingcarrier substrate903. The whole of the rest of the structure remains adhered to thedisplay substrate912, as illustrated in thecell wall assembly905 ofFIG. 23e.This surface is flat so that the resulting LC layer will be a constant thickness. Theelectrode structures910, however, are embedded at different distances from thecell wall912. The distances are set by the heights or thicknesses ofportions724,728,730 and734 of layer740 (now a dielectric covering layer for the electrode structures910).
• In this embodiment, one of thelayer740 is the full thickness of thebusbar908. It may be desirable to make the steps less than the full thickness of thebusbar908 to avoid increasing the switching threshold too much. The width of the step could be kept small to minimise the non-switching region. Alternatively, theinitial trench906 may be made somewhat shallower and the metal may be overplated to form abusbar908 that extends beyond thedielectric structures904 as illustrated inFIG. 24.
• FIG. 25 ilustrates adisplay device1000 having apixel999 withgreyscale capability Pixel999 comprises thecell wall assembly905 ofFIG. 23e,including afirst cell wall912aandfirst electrode structures910a,formed as previously described and in ohmic contact with thebusbar908. Thepixel999 in this example is a liquid crystal display device and has a layer of electro-optic material920 which comprises a nematic LC. Afirst surface alignment918ais provided on the innermost surface of thecell wall assembly905. Thesurface alignment918ain this example comprises a PABN surface textured with posts to provide bistable alignment to adjacent molecules of thenematic LC material920. Other bistable alignments could be used, or conventional alignment materials such as rubbed polyimide if the display is monostable, for example a supertwist or HAN cell.
• Asecond cell wall912bis of conventional construction, being formed from a flat glass or plastics material and havingsecond electrode structures910bformed thereon by a conventional etch technique using ITO. Asecond surface alignment918bis provided on thesecond electrode structures910b,in this example inducing homeotropic alignment in adjacent LC molecules. Means for distinguishing between different optical states are provided, in this example polarisers916 which are adhered to the outer surfaces of thecell walls912. It will be understood that surface alignments918 could be transposed; ie the PABN surface alignment could be provided on the innermost surface of the second cell wall and the homeotropic surface alignment could be provided on the firstcell wall assembly905. Thesecond cell wall912bmay be spaced apart from the firstcell wall assembly905 by conventional spacing means (not shown) for example microbeads or pieces of glass fibre or polymer fibre. Suitable spacing means are well known to those skilled in the art of LCD manufacture.
• The inner surfaces of bothcell walls912 are substantially planar and parallel to each other, and the layer ofnematic LC material920 is of substantially constant thickness. The shortest distance between theLC material920 and one of thefirst electrode structures910avaries within the area of the pixel illustrated inFIG. 25. Above a maximum threshold voltage all of the visible pixel area is in an ‘on’ state. For a bistable display, when the voltage is reduced or removed the pixel remains in the ‘on’ state. To switch the pixel to an ‘off’ state, a suitable pulse is applied.
• FIG. 26 illustratespixel999′, another embodiment ofpixel999. Thedisplay pixel999′ ofFIG. 26 is similar to that ofFIG. 25 except that the secondcell wall assembly905bis constructed similarly to that of the first cell wall assembly905a.Multi-level layer740 separates thesecond electrode structures910bfrom theLC920. The secondcell wall assembly905bmay be constructed by a similar transfer method to that used to make the first cell wall assembly905a.Thetransparent adhesive914bof the secondcell wall assembly905bmay be formed of the same adhesive material as the transparent adhesive914aof the first cell wall assembly. In this arrangement, the shortest distance between theLC material920 and one of thefirst electrode structures910avaries within the area of the pixel, as does the shortest distance between theLC material920 and one of the secondmulti-level layer740b.In this arrangement the cell may be symmetrical in a plane through theLC layer920 parallel to thecell walls912 and may be more easily constructed because the electrode variation may be shared between the two cell wall assemblies.
• FIG. 27 illustratespixel999″, another embodiment ofpixel999 in which thepolariser916 on theupper cell wall912ais provided on an inner surface, in this example between thefirst cell wall912aand the adhesive914, so that birefringence of thefirst cell wall912adoes not affect the display appearance. The switching voltage differs according to the shortest distance of theelectrode structure910aand theLC molecules920. EachMulti-level layer740 increases the switching threshold voltage. In order to switch the LC between stable states the electric field applied across the LC has to exceed a threshold. By putting the dielectric step between the electrode and the LC the electric field experienced by the LC will be reduced. Thus the applied voltage needed to switch the LC can be controlled by varying the thickness of the steps. In the illustration inFIG. 25, sufficient voltage has been applied viaelectrode structures910aand910bto alignLC molecules920a,in the outer regions, in the ‘on’ state. The applied voltage was insufficient to switchLC molecules920b,in inner regions, from the ‘off’ state. Increasing the amplitude of a switching pulse will cause more of the steps to switch and hence increase the proportion of the device that switches into one of the two states, ultimately reaching a fully-switched state as illustrated inFIG. 25. The eye averages the areas of the pixel that are in each state to give a perceived grey level. LC molecules under thebusbar908 inFIG. 27 are switched, but are not visible under the opaque busbar. The busbar is narrow (about 5 μm) so is not readily visible.
• Although the present disclosure has been described with reference to example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.

Claims (20)

1. An apparatus comprising:

a first electrode;

a second electrode;

a first polymeric layer between the first electrode and the second electrode, the first layer having portions, each portion including a specific amount of a cross-linking agent, wherein each portion has a distinct thickness for the specific amount of cross-linking agent.

2. The apparatus ofclaim 1, wherein each set includes at least three portions.

3. The apparatus ofclaim 1, wherein the first layer includes a photo-polymer.

4. The apparatus ofclaim 1, wherein the first layer includes bisphenol A epoxy resin.

5. The apparatus ofclaim 1, wherein the first layer includes at least 20% by solids of bisphenol A diglycidyl ether (BADGE).

6. The apparatus ofclaim 1 further comprising an electro-optical material between the first layer and the first electrode.

7. The apparatus ofclaim 6, wherein the first side of the first layer includes multiple levels.

8. The apparatus ofclaim 6, wherein the second side of the layer includes multiple levels.

9. The apparatus ofclaim 6, wherein the first layer is transparent and wherein the first electrode element is transparent.

10. The apparatus ofclaim 6, wherein the first layer is transparent and wherein the first electrode element is reflective.

11. The apparatus ofclaim 6, wherein the first layer is opaque.

12. The apparatus ofclaim 6 further comprising a second polymeric layer on an opposite side of the electo-optical material as the first polymeric layer, the second polymeric layer having second substantially similar second sets of portions, each portion of the second sets including a specific amount of a cross-linking agent, wherein each portion of the second sets has a distinct thickness for the specific amount of cross-linking agent

13. The apparatus ofclaim 12, wherein the second polymeric layer includes multiple levels on the same side of the second polymeric layer as the second electrode.

14. The apparatus ofclaim 12, wherein the second polymeric layer includes multiple levels on the same side as the electro-optical material.

15. The apparatus ofclaim 1, wherein at least a percentage of at least one portion is ramped.

16. A method comprising:

providing a layer of material;

selectively treating portions of the layer to form a pattern of multiple substantially similar sets of portions, wherein each set includes differently treated portions that exhibit different degrees of material volatization from the layer to form different thicknesses across the layer; and

forming electrodes on opposite sides of the layer.

17. A method comprising:

providing a first layer of material;

selectively treating portions of the first layer such a differently treated portions exhibit different degrees of material volatization from the first layer to form a first structure having different levels; and

applying one or more second layers of one or more materials over the levels and separating the first structure from the one or more second layers to form a second structure having a negative copy of the levels of the first structure.

18. The method ofclaim 17, wherein the levels include multiple substantially similar sets of levels, each set including portions having specific amounts of cross-linking agents, wherein each portion has a distinct thickness for the specified amount of the cross-linking agent.

19. The method ofclaim 17, wherein selectively treating comprises:

exposing the portions of the first layer to distinct exposure doses of radiation; and

heating the portions.

20. The method ofclaim 17 further comprising:

providing a substrate supporting a third layer of one or more materials; and

imprinting the third layer with the negative copy of the levels of the first structure.

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