Abstract:
The present invention replaces conventional lighting devices, such as incandescent lamps, fluorescent lamps, and LED lamps, with an integrated electro-luminescent film structure, subdivided into electrically isolated micro-panels. Ideally, the electro-luminescent structure comprises separate red, green and blue micro-panels providing a full range of color adjustment. Alternatively, the electro-luminescent film structure includes stacked groups of layers, in which each group emits a different color and is independently controllable.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/840,511 filed Aug. 17, 2007 now U.S. Pat. No. 7,616,272 which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a backlight for a liquid crystal display (LCD), and in particular to a LCD backlight comprised of an electro-luminescent multi-layered film. 
     BACKGROUND OF THE INVENTION 
     Liquid crystal displays (LCD&#39;s) are rapidly becoming the universally dominant display technology. Over 250 million large, i.e. &gt;10-inch, LCD flat-panel displays (FPDs) are built annually for the manufacture of televisions, desktop computer monitors and notebook computers, and over 1 billion smaller, i.e. &lt;10-inch, displays are built annually for other applications, such as mobile phones and personal digital assistants (PDAs). Since LCD is a passive, i.e. non-emissive, technology, the display assembly usually requires a backlighting unit (BLU) in order to function in the application. Accordingly, there is a very strong demand for BLUs, e.g. annual BLU sales are approximately $14 billion and growing strongly as FPDs rapidly displace conventional cathode ray tube (CRT) technology in virtually all applications. 
     At the current state-of-the-art, the BLU is typically constructed using cold-cathode fluorescent (CCFL) tubes mounted in a complex arrangement that results in a very costly subassembly. In fact, the BLU for a typical LCD display today accounts for 25% to 35% of the bill-of-materials (BOM) cost. Therefore, there is a very strong motivation in the industry to find alternative methods of backlighting that reduce the BOM cost. In addition, the CCFL component contains mercury, which is classed as a toxic substance, creating a further motivation for displacing CCFL. 
     In order to produce a color image, the state-of-the-art LCD technology must incorporate a color filter (CF) component, which must be finely aligned with the LCD pixels. The color filter is another very costly element, accounting for some 20% of the BOM cost. In addition, the color filter degrades the contrast ratio and, more importantly, degrades the efficiency of the display by more than a factor of three, thus adding to the backlight cost and seriously impacting the energy efficiency of the FPD and therefore of the end-product. 
     Despite the serious cost and performance shortcomings of conventional BLU technologies that have been in use and incrementally improved over the last twenty-five years, the industry has so far been unable to create a viable alternative, which adequately addresses the fundamental issues of cost and efficiency. 
       FIGS. 1 ,  2  and  3  illustrate the construction of a conventional LCD display, including polarizers  1  mounted on the front and back of the display for filtering incoming and outgoing light, i.e. only passing light of a certain polarization into the liquid crystal and only passing light of a different polarization out of the LCD. Sheets of glass  2  are provided for sandwiching the liquid crystals therebetween and providing substrates for the remaining elements. Seals  3  and spacers  4  provide the necessary distance between the sheets of glass  2  and contain the liquid crystal therebetween. Transparent electrodes  5 , e.g. a transparent conductive oxide (TCO) such as indium tin oxide (ITO), enable an electric field to be applied to the liquid crystal for altering the polarization of light passing therethrough, and therefore the amount of light that is able to pass through the top polarizer  1 . A hard coat layer  6  and a polyimide film  7  provide protective coatings for the TCOs  5 . Thin-film transistor (TFT) control elements  8  define a matrix of independently addressable pixels through which the passage of light is controlled. A color filter (CF) layer  9  is comprised of a matrix of alternating red, green and blue filters enabling the color of the transmitted light to be controlled. The color filter layer  9  is the major cost driver in this assembly, accounting for some 20% of the bill-of-materials (BOM) cost of the FPD and also has very low optical efficiency, reducing the brightness of the display by 75%. 
       FIG. 2  illustrates the construction of a typical BLU that is mounted against the LCD assembly in order to build the complete FPD panel. Multiple elements are required in order to distribute the light from the CCFL tube  10  for the required brightness and uniformity including a cylindrical reflector  11  and a flat reflector  12 . A wedge-shaped light guide panel (LGP)  13  redirects the light at a 90° angle through a diffuser sheet  14 , a vertical prism sheet  15 , a horizontal prism sheet  16 , and a protective sheet  17 . The BLU is typically supplied to the FPD maker as a complete subassembly that accounts for some 25%-35% of the BOM cost of the FPD. 
     An alternative method of backlighting, disclosed in U.S. Pat. No. 5,121,234 issued Jun. 9, 1992 to Kucera, consists of placing a panel of electro-luminescent (EL) material immediately behind the LCD display. This method can have a relatively low cost and enable a relatively simple and thin assembly compared with the CCFL approach. However, conventional EL technology, despite decades of development, has not been able to achieve brightness levels much beyond 100 cd/m 2 , which is two orders of magnitude less bright than required in applications such as televisions and computer displays. Furthermore, even the best available EL materials have been unable to achieve anywhere close to the color gamut required in those applications or even in small color display applications, such as mobile phones. Therefore, EL technology at the current state-of-the-art is suitable as backlighting only for displays where high brightness and wide color gamut are not requirements, such as monochromatic displays for instrumentation or backlights for mobile phone keypads. 
     An object of the present invention is to overcome the shortcomings of the prior art by providing a backlighting arrangement that reduces the existing BOM cost and also provides a substantial efficiency improvement. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to a display comprising: 
     an electro-luminescent film structure for emitting light including an array of separate light emitting micro-panels; 
     a first polarizer for filtering the light emitted from the electro-luminescent device, thereby selectively emitting light of a first polarization; 
     a liquid crystal layer for rotating the polarization of the light passing therethrough to a second polarization in response to an electric field applied thereto; 
     first and second electrodes for applying the electrical field to the liquid crystal layer including pixelating means for addressing individual pixels within at least one of the first and second electrodes, whereby the electric field is applicable to selected pixels for rotating the polarization of the light passing therethrough; and 
     a second polarizer for filtering the light emitted from the liquid crystal layer, thereby selectively passing light of the second polarization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in greater detail with reference to the accompanying drawings which represent preferred embodiments thereof, wherein: 
         FIG. 1  is a cross-sectional view of a conventional LCD display; 
         FIG. 2  is an exploded view of a conventional BLU; 
         FIG. 3  is an exploded isometric view of a conventional LCD display; 
         FIG. 4  is an exploded isometric view of an LCD display in accordance with the present invention; 
         FIG. 5   a  is a side view of an electro-luminescent structure of the display of  FIG. 4 ; 
         FIG. 5   b  is a side view of an alternative electro-luminescent structure of the display of  FIG. 4 ; 
         FIG. 5   c  is a side view of an alternative electro-luminescent structure of the display of  FIG. 4 ; 
         FIG. 5   d  is a side view of an alternative electro-luminescent structure of the display of  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of a layered light emitting film structure in accordance with the device of  FIG. 4 ; 
         FIG. 7   a  is a cross-sectional view of an alternative layered light emitting film structure in accordance with the device of  FIG. 4 ; 
         FIG. 7   b  is a cross-sectional view of an alternative layered light emitting film structure in accordance with the device of  FIG. 4 ; 
         FIG. 8  is a cross-sectional view of a multi-paneled electro-luminescent structure; 
         FIG. 9  is an exploded isometric view of an LCD display in accordance with an alternate embodiment of the present invention; 
         FIG. 10  is an exploded isometric view of an LCD display in accordance with an alternate embodiment of the present invention; 
         FIG. 11  illustrates a field sequential color system in accordance with the embodiment of  FIG. 10 ; 
         FIG. 12   a  is an isometric view of a layered light emitting film structure with independently controlled stacks for emitting different colors in accordance with the embodiment of  FIG. 10 ; 
         FIG. 12   b  is a top view of the layered light emitting film structure of  FIG. 12   a;    
         FIG. 13  is an exploded isometric view of an LCD display in accordance with an alternate embodiment of the present invention; 
         FIG. 14  is an exploded isometric view of an LCD display in accordance with an alternate embodiment of the present invention; and 
         FIG. 15  is an exploded isometric view of an LCD display in accordance with an alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 4 , a liquid crystal display  120  in accordance with the present invention includes a liquid crystal material  121  sandwiched between upper and lower transparent substrates, e.g. glass plates,  122  and  123 , respectively. A first transparent electrode  124 , e.g. a transparent conductive oxide (TCO) such as indium tin oxide, is mounted adjacent the liquid crystal material  121  on a lower surface of the upper transparent substrate  122  to be supported thereby, while a color filter layer  126  is mounted on an upper surface of the upper transparent substrate  122  to be supported thereby. In alternative embodiments, the color filter layer  126  may be mounted instead on the lower surface of upper substrate  122 , or on either surface of lower substrate  123 . A second transparent electrode  127 , e.g. a TCO such as ITO, is mounted adjacent the liquid crystal material  121  on an upper surface of the lower transparent substrate  123  along with thin film transistor (TFT) control elements  128 . A lower polarizer  129  filters the incoming light, whereby only light of a certain polarization, e.g. horizontally polarized, is transmitted to the liquid crystal material, while an upper polarizer  131  only enables the light of a different polarization, e.g. vertically polarized, to pass, i.e. light rotated to the different polarization by the liquid crystal material. 
     The transparent electrodes  124  and  127  enable an electric field to be applied to the liquid crystal material  121  for altering the polarization of light passing therethrough, and therefore the amount of light that is able to pass through the top polarizer  131 . The thin-film transistor (TFT) elements  128  controlling the TCO layer  127  define a matrix of independently addressable pixels, six or which are identified as  127   a  to  127   f , through which the passage of light is controlled. Other means for pixelating the TCO layer  127  are within the scope of the invention, as well as pixelating the first transparent electrode  124 . The color filter (CF) layer  126  is comprised of a matrix of alternating red, green and blue filter sections enabling the color of the transmitted light to be controlled by selectively activating the liquid crystal pixels beneath the different colored filter sections to control the amount of red, blue and green light to pass corresponding to a desired color. 
     One embodiment of an electro-luminescent solid-state device  135  according to the present invention, shown in  FIG. 5   a , incorporates a conductive substrate  26 , such as N-type or P-type silicon or a conductive film deposited on a substrate of glass. A light-emitting film structure  20  (“layered light emitting film structure”), including one or more relatively thin active layers with luminescent centers, e.g. (i) rare earth elements in an oxide matrix; (ii) silicon nano-particles in a silicon nitride matrix, or (iii) zinc oxide, is deposited onto the top of the conductive substrate  26 . The film structure  20  can be deposited by one of many suitable methods, such as plasma enhanced chemical vapor deposition (PECVD), molecular beam epitaxy, pulsed laser deposition, sputtering, and sol-gel processes. An upper optically-transparent electrode layer  21 , e.g. indium tin oxide (ITO), is mounted on the film structure  20 , which, along with a back electrical contact  25 , enables AC or DC power to be applied thereto. Preferably, the upper transparent electrode layer  21  has a thickness of from 150 to 500 nm. Preferably, the chemical composition and the thickness of the upper transparent electrode layer  21  are such that the light emitting structure  20  has a resistivity of less than 70 ohm-cm. To enhance adhesion or provide a diffusion barrier, an intermediate electrical contact layer  22 , e.g. TiN, may be positioned between the upper transparent electrode layer  21  and an upper electrical contact  23 , e.g. a metal such as aluminum. The electrical contact layer  22  provides an ohmic contact point between the upper electrode layer  21  and the upper electrical contact  23 , while the upper electrical contact  23  provides a suitable surface for wire bonding contact. Other suitable materials for the upper transparent electrode layer  21  and electrical contact layer  22  might alternatively be employed. A back reflector  24  can be provided between the film structure  20  and the substrate  26  to reflect light, which is internally emitted towards the substrate  26 , back towards the emitting surface, i.e. the upper electrode layer  21 . 
     In another embodiment of an electro-luminescent solid-state device  135  according to the present invention, shown in  FIG. 5   b , the lower electrode  25  is applied to the top of the substrate  26 , in which case the substrate  26  may be non-conductive. The lower electrode  25  may be on either side of, or combined with, the optional back reflector layer  24 . If the substrate  26  is transparent, e.g. glass, and the lower electrode  25  is also transparent, e.g. indium tin oxide (ITO), the back reflector layer  24  may be placed on the underside of the substrate  26 , while the lower electrode  25  is positioned between the substrate  26  and the film structure  20 , as in  FIG. 5   c . In another embodiment, shown in  FIG. 5   d , the light is emitted through the transparent substrate  26 , instead of through the upper electrode layer  21 . Accordingly, the upper electrode layer  21  is reflective, and the substrate  26  and lower electrode  25 , which is deposited onto the substrate  26 , are transparent. 
     The substrate  26 , on which the film structure  20  is formed, is selected so that it is capable of withstanding high temperatures in the order of 600° C. or more. Examples of suitable substrates include silicon or poly silicon, either of which can be n-doped or p-doped, e.g. with 1×10 20  to 5×10 21  of dopants per cm 3 , fused silica, high temperature glass, zinc oxide, quartz, sapphire, silicon carbide, or metal substrates. The substrate  26  can optionally have a thermally grown oxide layer, which oxide layer can be of up to about 2000 nm in thickness, a thickness of 1 nm to 20 nm being preferred. The substrate  26  can optionally have a deposited electrically conducting layer, which can have a thickness of between 50 nm and 2000 nm, but preferably between 100 nm and 500 nm. The thickness of the substrate is not critical, as long as thermal and mechanical stability is retained. 
     The layered light emitting film structure  20  can be comprised of a single active layer or of multiple active layers, each layer having an independently selected composition and thickness, for example: rare earth oxides or other semiconductor material with luminescent centers activated by impact ionization or impact excitation. In a preferred embodiment the active layers are comprised of rare earth elements, e.g. Er, Ce, Eu, Tb, in a silicon dioxide (SiO 2 ) matrix for the active layers, with SiO 2  for the buffer layers. Alternatively, the active layers may comprise semiconductor nano-particles, such as a group IV semiconductor (e.g. Si, Ge, Sn and PB) in a wide bandgap semiconductor or dielectric matrix, such as a group IV (e.g. Si, Ge, Sn and Pb) oxide or nitride matrix with or without rare earth doping elements and with or without carbon doping, as will hereinafter be described. By using active layers having different compositions, a multi-color structure can be prepared. For example, combining terbium layers, cerium layers and europium layers in a single multi-layer structure provides a structure that can luminesce at green (terbium), blue (cerium), and red (europium) or color combinations thereof, e.g. white. The layers can be either stacked or constructed side by side as separately controllable circuit elements. 
     One type of preferred layered light emitting film structure  20 , provided by an embodiment of the present invention, is a multi-layered emitter structure, shown by way of example in  FIG. 6 , which structure comprises multiple active layers  27  and  29 , e.g. terbium in a silicon dioxide matrix, with wide bandgap semiconductor or dielectric buffer layers  28 , e.g. silicon dioxide, otherwise known as “drift” or “acceleration” layers, deposited on the substrate  26 . Each of the active layers  27  and  29  has a thickness of from 1 nm to 10 nm. Each of the active layers  27  and  29  can comprise the same or different material, e.g. rare earth elements terbium and cerium, for generating the same or different wavelength of light, e.g. all of the active layers  27  emit one wavelength and all of the active layers  29  emit a second wavelength. The two wavelengths of light generated by the two sets of active layers  27  and  29  are combined together or with additional layers (not shown) to generate a desired color, e.g. white. The active layers  27  and  29  are separated by buffer layers  28 , such as silicon dioxide layers. The upper transparent electrode layer  21  is deposited on top of the multi-layer film structure  20 . There is no maximum thickness for the layered light emitting film structure, although a thickness of from 50 nm to 2000 nm is preferred and a thickness of from 150 nm to 750 nm is more preferred depending upon the available amount of voltage. 
     The structures shown in  FIG. 6  and the figures that follow show adjacent layers in contact with each other without intervening layers; however, additional layers can be utilized to the extent they do not interfere with the recited layers. Therefore, the terms coating and in contact do not exclude the possibility of additional intervening but non-interfering layers. 
     By embedding semiconductor nano-particles in a semiconductor nitride matrix, e.g. a group IV semiconductor, such as silicon, nano-particles in a group IV semiconductor, such as silicon, nitride matrix, the radiative lifetime of the semiconductor nano-particles can approach the nanosecond and/or sub-nanosecond regime due to the effect of surface passivation of the nano-particles by nitrogen atoms, and the effect of strong coupling of electron and hole wave functions of the excitons. However, uniformly deposited SiN x  films, in which semiconductor nano-particles are formed therein, generally have a relatively wide range of size, and a random spatial distribution, specifically the separation distances between nano-particles. In addition, semiconductor nano-particles formed in semiconductor nitride films may form connected small clusters when subjected to higher temperature, which would affect light emitting efficiency, thereby severely limiting device processing flexibility after film deposition. A combination of variations of nano-particles size and separation distance could result in significant impact on the electro-luminescence efficiency of semiconductor nano-particles structures formed in such films. 
     In the films in which semiconductor nano-particles are embedded in a semiconductor nitride matrix, current conduction in the films might be significantly affected by the high trap density of the semiconductor nitride host and hence impose detrimental effects on the effectiveness of injected charge carriers to gain energy from the electrical field to create excitons in the semiconductor nano-particles. However, the layered light emitting film structure according to the present invention eliminates all of the aforementioned problems by providing buffer (“drift” or “acceleration”) layers in between active layers of semiconductor nitride, thereby ensuring the proper distance between nano-particles. Moreover, providing thin active layers, i.e. nano-particle, size, the size of the nano-particles can be more closely controlled. 
     With particular reference to  FIGS. 7   a  and  7   b , a layered light emitting film structure  20 ′ or  20 ″, according to another embodiment of the present invention, is formed by a plurality of different stacks  32 ,  33  and  34  of organized layers, in which the active layers  35 ,  36  and  37  are separated by buffer layers  38 ,  39  and  40 , respectively, comprised of a pure wide bandgap semiconductor or dielectric material. 
     For layered light emitting film structures  20 ′ driven by AC voltage, a pair of electrodes  21 ′ and  25 ′ are positioned on opposite sides of the stack of layers  35  to  40 . Buffer layers  38  and  40  are disposed next to the electrodes  44  and  45 , respectively, as the current will flow in both directions as the voltage oscillates. Ideally one of the electrodes, e.g. electrode  21 ′, is transparent, e.g. ITO, and a reflective layer or coating  50  is added between one of the electrodes, e.g. electrode  25 , and the remaining stack of layers  35  to  40  to reflect any light back through the transparent electrode  21 ′. 
     In the case where the luminescent centers are comprised of nano-particles, the size of the nano-particles must be determined since the wavelength emitted is a function of nano-particle size. The size of the nano-particles, e.g. nanocrystals, is approximately equal to the thickness of the active layer  35 ,  36  and  37  (or  27  and  29  above) in which they reside (+10%). The size of the nano-particles in each active layer  35 ,  36  and  37 , i.e. the thickness of the active layer  35 ,  36  and  37 , is designed for a specific excitation energy to produce a desired colored light emission. A theoretical relationship between nano-particle diameter d (in nanometers) and excitation energy E (in electron-volts) for silicon nano-particles in a silicon dioxide matrix host doped with rare earth is given by:
 
 E= 1.143+5.845/( d   2 +1.274 d+ 0.905)−6.234/( d   2 +3.391 d+ 1.412);
 
     For example, ˜1.9 eV for red photons (d=2.9 nm), ˜2.3 eV for green photons (d=2.1 nm), or ˜2.8 eV for blue photons (d=1.6 nm). 
     For group IV, e.g. silicon, nano-particles in a, group IV, e.g. silicon, nitride matrix host without rare earth doping or for group IV, e.g. silicon, nano-particles in a silicon dioxide matrix host without rare earth doping the excitation energy equation to generate a specific excitation energy to produce a desired colored light emission from the nano-particles has been shown to be:
 
 E=E   0   +C/d   2  
 
     Where E 0 =1.16 eV and C=11.8 eV-nm 2    
     Accordingly, the thickness of the red light emitting layer, i.e. the diameter of the nano-particles in an active layer with silicon nano-particles in a silicon nitride matrix, is 4 nm, 3.25 nm for the green light emitting layer, and 2.6 nm for the blue light emitting layer. 
     The thickness of active layers with luminescent centers other than nano-particles, e.g. only rare earths in a suitable matrix, is typically determined empirically based on a tradeoff between the energy requirements and the brightness of the light. On the one hand, if the active layer is infinitely thin then the energy would be precisely known for the whole layer and therefore energy matching could be optimized; however, if the active layer is infinitely thin, there would be no luminescent centers and no light. The thicker the active layer is, the brighter the layer can be, since there would be more luminescent centers per sq mm; however, the energy will not be optimum throughout the entire thickness so there will be a loss of efficiency. 
     The thickness of the buffer layers  38 ,  39  and  40  (or  13  above) are determined as a function of the wavelength, and therefore of the required excitation energy of the corresponding active layers  35 ,  36  and  37  (or  27  and  29  above). For an electric field applied perpendicular to the plane of the layers  35  to  40 , an electron must gain sufficient energy from the applied electrical field to excite the luminescent centers to the correct energy—the energy gained in the buffer layers  38 ,  39  and  40  (measured in eV) is equal to the electric field multiplied by the thickness of the buffer layer  38 ,  39  or  40 . For example, for an applied electrical field of 5 MV/cm, the thickness of the buffer layer must be 3.8 nm or thicker to excite a luminescent center to 1.9 eV (1.9 eV/0.5 eV/nm=3.8 nm), 4.6 nm or thicker to excite a luminescent center to 2.3 eV, or 5.6 nm or thicker to excite a luminescent center to 2.8 eV. For layered light emitting film structures  20 ′ powered by AC electrical power, in which neighboring active layers, e.g.  35  and  36 , emit at different wavelengths, the intervening buffer layer, e.g.  38 , must be thick enough to excite the luminescent centers in the higher energy layer. 
     The layered light emitting film structure  20 ,  20 ′ or  20 ″ provides a great improvement in luminous flux (optical output power), efficiency (internal power conversion efficiency and external luminous efficacy), color rendering index (CRI), device reliability and lifetime, and device manufacturability/cost/yield of solid state light emitting devices based on any type of luminescent centers activated by impact ionization or impact excitation, e.g. rare earths or silicon nano-particles. 
     Rare earth ions may be incorporated into the active layers  35 ,  36  and  37 , into the buffer layers  38 ,  39  and  40 , or into both. The preferred structure incorporates rare earths only within the active layers  35 ,  36  and  37 , with a concentration such that the efficiency of energy transfer from the nano-particles to the rare earth ions is maximized and the radiative emission efficiency of the excited rare earth ions is maximized. Due to the complexity of the physical processes involved, optimization is generally an empirical process. The rare earth ion species placed within or next to a nano-particle active layer is selected to radiate at a wavelength matched to the excitation energy of the nano-particles within the active layer (or vice versa). Preferably, the rare earth elements are a lanthanide element, such as cerium, praeseodymium, neodynium, promethium, gadolinium, erbium, thulium, ytterbium, samarium, dysprosium, terbium, europium, holmium, or lutetium; however, they can also be selected to be an actinide element, such as thorium. 
     Other impurities, if required, will typically be incorporated only within the nano-particle active layers  35 ,  36  or  37 , although they could be placed anywhere within the structure  20 ,  20 ′ or  20 ″. For example, since observations have determined that the measured excitation energy of a nano-particle is not as high as expected theoretically, carbon atoms may be required to raise the excitation energy of the nano-particles transferred to the rare earth ions in the wide bandgap semiconductor or dielectric, e.g. silicon oxide, matrix. 
     The buffer layers  38 ,  39  and  40  should be of the highest quality, i.e. dense with few defects, achievable with such materials, within the capabilities of a specific processing technology, whereby the device lifetime and reliability under a high applied electric field will be maximized. 
     Silicon-rich silicon oxide, with or without carbon and rare earth doping, for the active layers  35 ,  36  and  37 , and silicon dioxide for the buffer layers  38 ,  39  and  40  are the preferred materials in the layered light emitting film structure. Other material systems, such as silicon-rich silicon nitride with or without rare earth doping for the active layers  35 ,  36  and  37 , and silicon nitride for the buffer layers  38 ,  39  and  40 , can also be used in this layered light emitting film structure. Rare earth oxides, which also act as luminescent centers, can also be used in the active layers  35 ,  36  and  37 . Zinc oxide is also a suitable material for use in the active layers as a luminescent center. Alumina (aluminum oxide) is also a suitable matrix in which to embed the luminescent centers such as rare earths. 
     The density of the luminescent centers in any layer can be changed by varying the deposition conditions in the layer during deposition and by varying the annealing conditions (annealing temperature and time, for example). The luminescent center density, within the active layers  35 ,  36  and  37 , is preferably as high as possible to increase the intensity of emitted light, while still remaining below the density that would result in interactions between the luminescent centers, i.e. quenching, or agglomeration thereof, i.e. clustering. 
     The total number of repeated layers  35  to  40  in the layered light emitting film structure  20 ,  20 ′ or  20 ″ is determined by the voltage that will be applied to the entire film and by the electric field required for efficient and reliable operation. In a simple approximation, very little voltage is dropped across the active layers  35 ,  36  and  37 , so that the number of layers required will be equal to the applied voltage divided by the electric field and divided by the thickness of the buffer layers  38 ,  39  and  40 . For example, if the applied voltage is 110 V, the desired electric field within one dielectric layer  39  is 5 MV/cm (i.e. 0.5 V/nm), and the desired excitation energy is 2.3 eV, then the dielectric layer is 4.6 nm thick, and the total number of repeated layer pairs  36 / 39  is:
 
(110 V )/(0.5 V/nm )/(4.6 nm )=48 layers or pairs.
 
     A single color can be emitted by the layered light emitting film structure  20 ,  20 ′ or  20 ″ by repeating identical pairs of active and dielectric layers, e.g. the layered light emitting film structure  20  with identical active layers  27  and  29 . Mixed colors, e.g. white, can be emitted by the layered light emitting film structure  20 ,  20 ′ or  20 ″, since the entire film will comprise several layer pairs for each constituent color. For example, N pairs of active/dielectric layers altogether may comprise k pairs for blue  35 / 38 , m pairs for green  36 / 39 , and n pairs for amber/red/orange  37 / 40 , where k+m+n=N. The number of each of the color pairs, e.g.  35 / 38 ,  36 / 39  and  37 / 40 , can be varied so that any desired color rendering index (CRI) can be achieved. For example, a warm white requires more pairs of red than blue  35 / 38 , while a cool white requires the opposite. 
     For white or other multi-color light emission, and for a device in which a back reflector  50  is included in the structure, it is preferable to place the lowest energy (longest wavelength, e.g. red) emission layers nearest to the reflector  50  and the highest energy (shortest wavelength, e.g. blue) layers nearest to the emitting surface. Layers emitting intermediate wavelengths, e.g. green, are placed intermediate the layers emitting the longest and shortest wavelengths. Alternatively, in the case in which a transparent substrate is employed, the reflective layer  50  may be positioned on the opposite side of the substrate. 
       FIG. 7   b  illustrates a layered light emitting film structure  20 ″ powered by DC electrical power, i.e. an anode  21 ″ and a cathode  25 ″. The active layers  35 ,  36  and  37  and most of the buffer layers  38 ,  39  and  40  are identical to those in the layered light emitting film structure  20 ′; however, since the electrons only travel in one direction, the intervening buffer layers between different types of active layers must be the correct thickness to excite the luminescent centers in the active layer closer to the anode  25 ″. Accordingly, the layered light emitting film structure  20 ″ is preferably terminated by one of the first buffer layers  38  at the cathode  21 ″ and by an active layer  37  at the anode  25 ″. Moreover, since the electrons travel only in one direction, i.e. from the cathode to the anode, one of the second buffer layers  39  is between the first stack  32  and the second stack  33 , and one of the third buffer layers  40  is between the second stack  33  and the third stack  34 . 
     In  FIG. 4 , the electro-luminescent solid-state device  135  is illustrated as having a plurality of uniformly or independently controlled micro-panels, six of which are indicated by  135   a  to  135   f , which substantially align with an N×M array of pixels, six of which are indicated by  127   a  to  127   f , defined by the TFT elements  128 , whereby light only is generated where it is useful, i.e. not under the TFT pixelation elements; however, it may be advantageous, from a manufacturing point of view, to have the light generated quasi uniformly to eliminate the need to align the separate substrates, whereby the EL device  135  emits light continually, and only the liquid crystal pixels control the passage of light. Accordingly, only a few (two to fifty) large micro-panels, each of which provides light to several of the pixels, is possible. 
     Studies into the planar breakdown of thin oxides, such as the ones used for the upper and lower electrode layers  21  and  25 , respectively, have shown that the edges of the upper electrodes  21  cause an enhanced concentration of the electric field over the layered light emitting film structure  20 . Placing a field oxide region below the upper electrode layers  21  has been suggested in International Patent Application No. WO 2007/073601, published Jul. 5, 2007, by the applicant of the present application, which is incorporated herein by reference, to minimize current injection below the upper electrode layer  21 , thereby maximizing current flow in the light emitting structure  20  adjacent to the upper electrode layer  21 . The edges of the upper electrode  21 , which are over the thick field oxide region, exhibits potential contours that are more spread out resulting in a reduction of the electric field at the edge of the upper electrodes  21 , which is due to the increased thickness of the field oxide region. The thick field oxide region further imposes a potential barrier to direct current flow between the upper and lower electrodes  21  and  25  and the substrate  26 . The incorporation of the thick field oxide into the EL device  135  significantly reduced the incident of edge related electric field concentration and breakdown. 
     An EL device based on the thick field oxide does not necessarily allow for the formation of arbitrarily large area micro-panels, because asperities or non-uniform film thicknesses, caused from the deposition techniques, can result in localized increases in the electric field under bias leading to the formation of breakdown spots or hot spots in the bottom of the light emitting structure. At low excitation power levels, the planar breakdowns that take place in the active area of the EL device  135  well tend to be of the self healing type. As the bias across the EL device  135  is increased, a breakdown or a hot spot forms where it is believed that the current on a microscopic scale increases suddenly and this leads to a rupture of the dielectric properties of the layered light emitting film structure  20  and a large amount of energy stored in the cables connecting the EL device  135  to the power source is suddenly released. As a result of this, the layered light emitting film structure  20  and the upper electrode layers  21  in the immediate surrounding area are vaporized and a crater is left behind. The defect that was the site of the initial breakdown/rupture has also been removed and ejected by this process and the pixel is found to continue to operate until the bias is increased and the next weakest point in the layered light emitting film structure  20  is found and the process repeats itself. 
     The aforementioned mode of breakdown is typically self healing; however, if the bias is large enough, when there is a rupture of the layered light emitting film structure  20  in a large area pixel, the breakdown will cease to be self healing and will become propagating in nature. Accordingly, the breakdown will continue with a burning action/arc in which the layered light emitting film structure  20  and the upper electrodes  21  in effect burn up. If left unchecked, the burning can continue with the near complete consumption of the entire active area well in the layered light emitting film structure  20  of the EL device  135 , unless the current to the EL device  135  is terminated. 
     With particular reference to  FIG. 8 , to overcome the problems with large area emitting structures, such as propagating breakdown, the total emitting area of the layered light emitting film structure  20  is subdivided into smaller area micro-panel emitters, e.g.  135   a  to  135   f , that are laterally isolated from one another by the presence of thick field oxide regions  65 . The presence of the thick field oxide regions  65  between adjacent micro-panels, e.g.  135   a  to  135   f , serves to electrically isolate the light emitting structure  20  and the upper electrode  21  from the underlying substrate  26 , whereby connections to metal power buses  66  can be made to the upper electrode  21  without resulting in a breakdown directly under the metal power buses  66 . Secondly the thick field oxide regions  65  serve as a barrier to disrupt the propagating nature of a high bias failure. 
     To construct the EL device  135 , the micro-panel emitters, e.g.  135   a  to  135   f , are patterned and the thick field oxide regions  65  are grown using a LOCOS technique. Alternatively, a thick field oxide layer can be grown over the substrate  26  and then etched back to the bare substrate  26  defining the thick field oxide regions  65 . As a result of either initial step, device wells are formed surrounded by the thick field oxide regions  65  to provide lateral isolation from adjacent device wells. Subsequently, the layered light emitting film structure  20 ,  20 ′ or  20 ″ is deposited using any suitable technique, e.g. sputtering, spin on, LPCVD, PECVD, ALE, MOCVD, or MBE techniques. The layered light emitting film structure  20  is deposited as a blanket layer or multi-layer structure over top of a plurality of device wells, i.e. micro-panels  135   a  to  135   f , and a plurality of field oxide regions  65  requiring no patterning and etching as isolation between micro-panel, e.g.  135   a , to micro-panel, e.g.  135   b , is provided by the thick field oxide regions  65 . The upper and lower electrodes  21  and  25  are then deposited as blanket layers, again using sputtering, spin on, LPCVD, PECVD, ALE, MOCVD, or MBE techniques. The upper electrode  21  is conductive and forms the upper contact electrode for all of the micro-panels, e.g.  135   a  to  135   f , simultaneously. Lateral isolation between adjacent micro panels, e.g.  135   a  to  135   f , is provided by the thick field oxide regions  65 . A schematic representation of the micro-paneled structure is shown in  FIG. 8 , in which the thick field oxide regions  65  separating the two device wells, i.e. micro-panels  135   a  and  135   b . In a large area emitter, there would be many of the micro-panels arranged in a larger array. 
     Once a propagating breakdown event is established in a micro-panel, e.g.  135   a  to  135   f , the burn front will move to consume both the layered light emitting film structure  20  and the upper electrode layer  21  laterally as long as the current source to the devices is maintained. As the burn front approaches the edge of the device well, i.e. the micro-panel, it will start to travel up and out of the device well as both the layered light emitting film structure  20  and the upper electrode  21  are continuous on top of the thick field oxide regions  65 . When this happens, the impedance of the arc will start to increase and there will be a tendency for the arc to self extinguish as the arc is established between the upper electrode  21  and the substrate  26 . The extinguishing of the arc is due to the reduction of the electric field across the emissive layer stack of the upper electrode  21  as the burn front moves up the thick field oxide region  65  and away from the substrate  26 . Accordingly, the inclusion of the thick filed oxide regions  65  between adjacent micro-panels  135   a  and  135   b  causes a propagating breakdown event to become an isolated event that is localized in the originating micro-panel. The breakdown event is effectively isolated by the presence of the thick field oxide regions  65  rendering the rest of the micro-panels in the large area array largely unaffected where they continue to operate under bias, whereby the thick field oxide regions  65  provide a built in self limiting mechanism by which propagating breakdowns are terminated without adjusting the bias current. 
     There are additional benefits to designing large area emitters as a micro-paneled device. Most importantly, the metallization interconnect that supplies power via the upper electrode  21  to reduce spreading resistance and parasitic resistance effects associated with the upper electrode  21  can be run along the upper electrode  21  on top of the thick field oxide regions  65 , whereby the capacitance associated with the metallization interconnect is minimized and the metal does not eclipse any light generated. 
     In an alternate embodiment of a liquid crystal display  220 , illustrated in  FIG. 9 , the color filter layer  126  and the electro-luminescent layer  135  from the device of  FIG. 4  are replaced by a multi-color electro-luminescent solid-state device  235 , which has an array of colored micro-panels, which alternate in color between red, green and blue (R, G &amp; B). The remaining elements in the display  220 , i.e. the upper and lower glass plates  122  and  123 , the TCO layers  124  and  127 , the TFT elements  128 , and the upper and lower polarizers  131  and  132 , are identical or similar to like numbered elements in the device of  FIG. 4 . Typically, each pixel  127   a  to  127   f  in the liquid crystal display  220  has at least one of each of the color micro-panels, i.e. R, G &amp; B, associated therewith; however in another possible embodiment, illustrated in  FIG. 9 , each colored micro-panel  235   a  to  235   f  has only one TCO pixel  127   a  to  127   f  aligned therewith. In the LCD  220 , the colored micro-panels  235   a  to  235   f  can be kept on at all times, and the pixels  127   a  to  127   f  determine the amount of each color that passes through the LCD display  220 ; however, independent control of the micro-panels  235   a  to  235   f  is also possible by providing addressing means with drivers and control electronics. In another possible embodiment one of each of the colored panels  235   a  to  235   f  is aligned with several LC pixels  127   a  to  127   f ; however, having a panel to LC pixel ratio less than or greater than one is also possible, depending on the quality of the LC display required. The separate colored light emitting panels are several times more efficient than filtering the colored components out of white light with a color filter, as in the prior art. Moreover, by eliminating the light diffusers and other interconnect components an even higher efficiency can be achieved. 
     In an alternate embodiment, illustrated in  FIG. 10 , a color liquid crystal display  320  includes a multi-color light panel  325 , in which each pixel  127   a  to  127   f  has a plurality of micro-panels, e.g. micro-panels  325   a  to  325   i , including one or more of each color (R, G &amp; B) aligned therewith. Accordingly, a micro-controller  100  can control the pixels  127   a  to  127   f  and the micro-panels  325   a  to  325   i  under each pixel to provide a field sequential color (FSC) liquid crystal display. The pattern of micro-panels  325   a  to  325   i  may be finely defined so as to present an appearance of uniform color, e.g. white, behind each pixel  127   a  to  127   f . For the same reason, the different colored micro-panels  325   a  to  325   i  may be stacked on top of each other rather than side by side. The illustrated embodiment includes three red  325   c ,  325   e ,  325   g , three blue  325   b ,  325   d ,  325   i , and three green  325   a    325   f ,  325   h  micro-panels per LC pixel  127   a  to  127   f , although any number of micro-panels, e.g. one micro-panel to a plurality of pixels, is possible depending on the required quality of the display  320 . The remaining elements in the LCD display  320 , i.e. the upper and lower glass plates  122  and  123 , the TCO layers  124  and  127 , the TFT elements  128 , and the upper and lower polarizers  131  and  132 , are identical or similar to like numbered elements in the device of  FIGS. 4 and 9 . 
     The operation of a typical field sequential color (FSC) device  320  is as follows. All of the pixels  127   a  to  127   f  that require red light are activated by turning on the red micro-panels  325   c ,  325   e ,  325   g  under each pixel  127   a  to  127   f  that requires red, then all of the pixels  127   a  to  127   f  that require green light are activated by turning on the green sub-pixel micro-panels  325   c ,  325   e ,  325   g  under each pixel  127   a  to  127   f  that requires green light, and then all of the pixels  127   a  to  127   f  that require blue light are activated by turning on the blue sub-pixels micro-panels  325   b ,  325   d ,  325   i  under each pixel  127   a  to  127   f  that requires blue sequentially, whereby the LCD  320  passes the corresponding portions of each color making up the desired image. The viewer&#39;s eye integrates the combination of the three colors to form a full color image. In the example illustrated in  FIG. 11 , the red sub-pixels  325   c ,  325   e ,  325   g  corresponding to selected pixels making up the flower and pot are activated first, followed by the activation of the green sub-pixel micro-panels  325   c ,  325   e ,  325   g  corresponding to selected pixels making up the stem, leaves and pot, and finally by the activation of the blue sub-pixel micro-panels  325   b ,  325   d ,  325   i  corresponding to selected pixels making up the pot and base. The combination of the sequenced colors provides the viewer with a red flower, green leaves and stem, a blue base, and a white pot. The white color formed by the combination of the red, green and blue. The colored sub-pixel micro-panels  325   a  to  325   i  can be any set fraction, e.g. greater than or less than 1, of the size of the LC pixel  127   a  to  127   f  and do not have to be located only under them. 
     Electrical connections have to be provided so that all of the micro-panels of each color can be turned on and off as a group (e.g., a red group, a green group and a blue group). The different colored micro-panels are shown separated laterally; however, they may be stacked vertically for denser packing at the cost of process complexity. In the embodiment illustrated in  FIGS. 12   a  and  12   b , each pixel  127   a  to  127   f  has a single corresponding micro-panel, which is formed by a plurality of different stacks  32 ,  33  and  34  of organized layers, in which the active layers  35 ,  36  and  37  are separated by buffer layers  38 ,  39  and  40 , respectively, comprised of a pure wide bandgap semiconductor or dielectric material, as disclosed above with reference to  FIGS. 7   a  and  7   b.    
     As above, for layered light emitting film structures driven by AC voltage, a pair of electrical contacts  52  and  53  are positioned on opposite sides of the stack of layers  32 , while a separate pair of independently controllable electrical contacts  54  and  55  are positioned on opposite sides of the stack of layers  33 , and a separate pair of independently controllable electrical contacts  56  and  57  are positioned on opposite sides of the stack of layers  34 . Buffer layers  38 ,  39  and  40  are disposed between active layers  35 ,  36  and  37 , respectively and next to the electrical contacts  52  to  56 , as the current will flow in both directions as the voltage oscillates. Ideally the electrical contacts  52  to  56  are transparent, e.g. ITO, and the reflective layer or coating  50  is added between the electrode  57  and the remaining stack of layers  32  to  34  to reflect any light back through the stacks. In addition, isolation layers  59 , between adjacent electrical contacts  53 / 54  and  55 / 56 , must be provided in order that each colored stack  32 ,  33  and  34  can be independently controlled. 
     With reference to  FIG. 13 , another display  420 , in accordance with the present invention, includes the liquid crystal layer  121  with an upper glass plate  122 , an upper electrode layer  124 , a color filter  126 , and an upper polarizer  131 , as in the display  120  of  FIG. 4 . However, instead of a lower glass plate  123  with TCO pixel layer  127  pixelated by TFT elements  128 , the display  420  includes a electro-luminescent solid-state device  435  with a lower electrode layer  427  pixelated by TFT elements  428  (or other suitable means) patterned directly thereon, thereby eliminating the need for a lower glass plate  123  and separate activating electronics for both the liquid crystal layer  121  and the EL device  435 . A polarizing layer  432  is mounted on and supported by the EL device  435  adjacent the liquid crystal layer  121  rather than on the underside of the lower glass plate  123 , as in  FIG. 4 . Preferably, the EL device  435  is similar or identical to the aforementioned EL device  135  with two or more micro-panels generating white light. 
     With reference to  FIG. 14 , another display  520 , in accordance with the present invention, includes the liquid crystal layer  121  with an upper glass plate  122 , and an upper polarizer  131 , as in the display  220  of  FIG. 9 . However, instead of a lower glass plate  123  with lower electrode layer  127  defined by TFT elements  128 , the display  520  includes a colored electro-luminescent solid-state device  535 , similar to multi-color light micro-panels  235  or  325 , with a lower electrode layer  527  pixelated by TFT elements  528  patterned directly thereon, thereby simplifying and reducing the cost of the entire assembly. A polarizing layer  532  is mounted on and supported by the EL device  535  adjacent the liquid crystal layer  121  rather than on the underside of the lower glass plate  123 , as in  FIG. 9 . The material forming the polarizing layer  532  is compatible with LC chemistry and/or any surface layers usually patterned on the inner surface of the device  535 . In a variant of this configuration, the TCO layers  124  and  527  may be reversed, i.e. the TFT-controlled TCO layer ( 527 / 528 ) may be placed on the upper glass plate  122  and the TCO rows  124  placed on the emitter panel  535 . In either of these cases, the emissive film, e.g.  20 ,  20 ′,  20 ″, may be placed on either surface of the emitter panel  535 . 
     With reference to  FIG. 15 , another display  620 , in accordance with the present invention, includes the liquid crystal layer  121  with an upper glass plate  122 , and an upper polarizer  131 , as in the displays  220  and  520  of  FIGS. 9 and 14 , respectively. However, instead of a lower glass plate  123  with lower electrode layer  127  pixelated by TFT elements  128 , the display  620  includes a colored electro-luminescent solid-state device  635 , similar to multi-color light micro-panels  235  or  325 , with a lower electrode layer  627  pixelated by TFT elements  628  patterned directly thereon, thereby simplifying and reducing the cost of the entire assembly. A polarizing layer  632  is patterned directly on the EL device  635  adjacent the liquid crystal layer  121  rather than on the underside of the lower glass plate  123 , as in  FIG. 9 . Preferably, the polarizing layer  632  comprises a thin film polarizer, which includes arrays of thin parallel lines (or grooves) etched in the materials. Advanced LC designs already nanostructure the inner surface of the display to enhance performance, the thin film polarizer in accordance with the present invention would be an extension of the nano-structured processes. The material forming the polarizing layer  632  is compatible with LC chemistry and/or any surface layers usually patterned on the inner surface of the device  635 . In a variant of this configuration, the TCO layers may be reversed, ie the TFT-controlled TCO layer ( 527 / 528 ) may be placed on the upper glass plate  122  and the TCO rows  124  placed on the emitter panel  535 . In any of these cases, the emissive film may be placed on either surface of the emitter panel  535 . 
     With reference to any of the LCD displays  120 ,  220 ,  320 ,  420 ,  520  and  620  in  FIG. 4 ,  9 ,  10 ,  13 ,  14  or  15 , additional control circuitry in micro-controllers  100  may be provided for controlling the voltage supplied to each micro-panel, such that groups of selected micro-panels  135   a  to  135   f  or  235   a  to  235   f  or  325   a  to  325   g  in the EL devices  135 ,  235 ,  325 ,  435 ,  535  or  635  may be dimmed in areas of the display in which the picture is momentarily darker, e.g. dimmed in pixels adjacent to black or closed pixels; or brightened as a group in areas of the display in which the picture is momentarily brighter, e.g. brightened in pixels adjacent to white or open pixels. As a result, enhanced contrast and reduced power consumption is possible. 
     Furthermore, additional control circuitry in the micro-controllers  100  may also enable rows of the micro-panels, e.g.  135   a  to  135   f  or  235   a  to  235   f  or  325   a  to  325   g , in the layered light emitting film structures  135 ,  235 ,  325 ,  435 ,  535  or  635  to be sequenced as a group in synchronism with the refresh scanning of the LCD pixel data. Accordingly, in the time when the LCD pixels are neither “ON” or “OFF” the micro-panels are turned off and do not emit light, thereby reducing motion artifacts, providing enhanced contrast, and reducing power consumption.