PATENT DOCUMENT

Publication Number: US-8558978-B2
Application Number: US-37136809-A
Country: US
Kind Code: B2

Title: LCD panel with index-matching passivation layers

Abstract:
A liquid crystal display (LCD) having one or more index-matching layers is provided. In one embodiment, an index-matching passivation layer is provided between two additional layers of the LCD. The index-matching passivation layer may include a refractive index greater than a first layer of the two additional layers and less than a second layer of the two additional layers. Various additional devices and methods are also provided.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 one or more input structures; 
 a storage structure encoding one or more executable routines; 
 a processor capable of receiving inputs from the one or more input structures and of executing the one or more executable routines when loaded in a memory; and 
 a liquid crystal display (LCD) capable of displaying an output of the processor, wherein the LCD includes:
 a first passivation layer disposed in contact with a second passivation layer, wherein the first passivation layer includes a refractive index less than that of the second passivation layer; 
 a plurality of electrodes formed on a common surface of the first passivation layer; and 
 
 a liquid crystal layer disposed over the plurality of electrodes, wherein the electrodes of the plurality of electrodes are spaced apart along the common surface such that portions of the liquid crystal layer are disposed between the electrodes and the first passivation layer, wherein the first passivation layer includes a plurality of regions having different refractive indices, wherein the plurality of regions includes a first region in contact with an electrode of the plurality of electrodes and a second region in contact with the liquid crystal layer, wherein the first region of the first passivation layer has a refractive index between those of the second passivation layer and the electrode, while the second region of the first passivation level has a refractive index between those of the second passivation layer and the liquid crystal layer. 
 
     
     
       2. The electronic device of  claim 1 , wherein the first region of the first passivation layer has a refractive index of approximately 1.9. 
     
     
       3. The electronic device of  claim 1 , wherein the second region of the first passivation layer has a refractive index of approximately 1.74. 
     
     
       4. The electronic device of  claim 1 , wherein the liquid crystal layer has a refractive index of approximately 1.5. 
     
     
       5. The electronic device of  claim 1 , wherein the electrode has a refractive index of approximately 1.8. 
     
     
       6. The electronic device of  claim 1 , wherein the second passivation layer has a refractive index of approximately 2.0. 
     
     
       7. The electronic device of  claim 1 , wherein the LCD comprises a fringe field switching LCD panel. 
     
     
       8. A liquid crystal display, comprising:
 a first passivation layer disposed in contact with a second passivation layer, wherein the first passivation layer includes a refractive index less than that of the second passivation layer; 
 a plurality of electrodes formed on a common surface of the first passivation layer; and 
 a liquid crystal layer disposed over the plurality of electrodes, wherein the electrodes of the plurality of electrodes are spaced apart along the common surface such that portions of the liquid crystal layer are disposed between the electrodes and the first passivation layer, wherein the first passivation layer includes a plurality of regions having different refractive indices, wherein the plurality of regions includes a first region in contact with an electrode of the plurality of electrodes and a second region in contact with the liquid crystal layer, wherein the first region of the first passivation layer has a refractive index between those of the second passivation layer and the electrode, while the second region of the first passivation level has a refractive index between those of the second passivation layer and the liquid crystal layer. 
 
     
     
       9. The liquid crystal display of  claim 8 , wherein the first region of the first passivation layer has a refractive index of approximately 1.9. 
     
     
       10. The liquid crystal display of  claim 8 , wherein the second region of the first passivation layer has a refractive index of approximately 1.74. 
     
     
       11. The liquid crystal display of  claim 8 , wherein the liquid crystal layer has a refractive index of approximately 1.5. 
     
     
       12. The liquid crystal display of  claim 8 , wherein the electrode has a refractive index of approximately 1.8. 
     
     
       13. The liquid crystal display of  claim 8 , wherein the second passivation layer has a refractive index of approximately 2.0. 
     
     
       14. The liquid crystal display of  claim 8 , wherein the liquid crystal display comprises a fringe field switching liquid crystal display panel.

Description:
BACKGROUND 
     1. Field of the Invention 
     This relates generally to electronic display panels, such as liquid crystal displays. 
     2. Description of the Related Art 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Liquid crystal displays (LCDs) are commonly used as screens or displays for a wide variety of electronic devices, including such consumer electronics as televisions, computers, and handheld devices (e.g., cellular telephones, audio and video players, gaming systems, and so forth). Such LCD devices typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, such LCD devices typically use less power than comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to minimize power usage. 
     The performance of an LCD may be measured with respect to a variety of factors. For example, the brightness of the display, the visibility of the display when viewed at an angle, the refresh rate of the display, and various other factors may all describe an LCD and/or determine whether a display will be useful in the context of a given device. With respect to brightness, it is noted that the perceived brightness of an LCD is influenced by a number of factors. For example, an LCD panel typically includes a number of transparent layers through which light passes, and that these layers may have different refractive indices. As light passes between the various materials of these layers, some of the light may be reflected at interfaces between the materials, thus reducing the amount of light that passes completely through the LCD panel and is output to a user. 
     SUMMARY 
     Certain aspects of embodiments disclosed herein by way of example are summarized below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms an invention disclosed and/or claimed herein might take, and that these aspects are not intended to limit the scope of any invention disclosed and/or claimed herein. Indeed, any invention disclosed and/or claimed herein may encompass a variety of aspects that may not be set forth below. 
     The present disclosure relates to increasing the light transmission of electronic display pixels and panels. In accordance with the present disclosure, a display panel may include one or more intermediate index-matching layers interposed between other layers of the display panel having different refractive indices. More particularly, such an index-matching layer may have a refractive index between those of other adjacent layers, and may reduce the degree to which light is reflected as light passes through the display panel, such as an LCD panel. Moreover, by reducing the amount of light internally reflected by the display panel, the amount of light ultimately output from the display panel, such as to a user, is increased. While an index-matching layer may have any refractive index between those of other adjacent and opposing layers, in one embodiment the refractive index of the index-matching layer may be approximately equal to the square root of the product of the refractive indices of the adjoining layers. 
     Various refinements of the features noted above may exist in relation to various aspects of the present invention. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present invention alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of embodiments of the present invention without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the invention may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a block diagram of exemplary components of an electronic device, in accordance with aspects of the present disclosure; 
         FIG. 2  is a front view of a handheld electronic device in accordance with aspects of the present disclosure; 
         FIG. 3  is a view of a computer in accordance with aspects of the present disclosure; 
         FIG. 4  is an exploded view of exemplary layers of a pixel of an LCD panel, in accordance with aspects of the present disclosure; 
         FIG. 5  is a circuit diagram of switching and display circuitry of LCD pixels, in accordance with aspects of the present disclosure; 
         FIG. 6  is a partial cross-section of an LCD pixel in accordance with aspects of the present disclosure; 
         FIG. 7  is a partial cross-section of an LCD pixel in accordance with aspects of the present disclosure; 
         FIG. 8  is another partial cross-section of the LCD pixel of  FIG. 6  in accordance with aspects of the present disclosure; 
         FIG. 9  is a partial cross-section of another LCD pixel embodiment in accordance with aspects of the present disclosure; 
         FIG. 10  is another partial cross-section of the LCD pixel of  FIG. 6  in accordance with aspects of the present disclosure; 
         FIG. 11  is a partial cross-section of an additional LCD pixel in accordance with aspects of the present disclosure; and 
         FIG. 12  is a partial cross-section of another embodiment of an LCD pixel in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments of the present invention will be described below. These described embodiments are only exemplary of the present invention. Additionally, in an effort to provide a concise description of these exemplary embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, while the term “exemplary” may be used herein in connection to certain examples of aspects or embodiments of the presently disclosed subject matter, it will be appreciated that these examples are illustrative in nature and that the term “exemplary” is not used herein to denote any preference or requirement with respect to a disclosed aspect or embodiment. 
     The application is generally directed to increasing transmittance of pixels in an LCD panel. In some embodiments, such an increase may be achieved by including an index-matching passivation layers between two other layers of the panel that have refractive indices different from one another. For instance, one embodiment of an LCD pixel may include various electrode layers, passivation layers, a gate insulation layer, substrate layers, a liquid crystal layer, and the like. Some of these layers have refractive indices different from one another, causing light passing through these layers to be reflected at interfaces between the layers having different refractive indices. By including index-matching layers between other layers having different refractive indices, the total amount of light internally reflected at the layer interfaces is reduced, and transmittance is thereby improved. 
     With these foregoing features in mind, a general description of suitable electronic devices using LCD displays having such increased light transmittance is provided below. In  FIG. 1 , a block diagram depicting various components that may be present in electronic devices suitable for use with the present techniques is provided. In  FIG. 2 , one example of a suitable electronic device, here provided as a handheld electronic device, is depicted. In  FIG. 3 , another example of a suitable electronic device, here provided as a computer system, is depicted. These types of electronic devices, and other electronic devices providing comparable display capabilities, may be used in conjunction with the present techniques. 
     An example of a suitable electronic device may include various internal and/or external components which contribute to the function of the device.  FIG. 1  is a block diagram illustrating the components that may be present in such an electronic device  8  and which may allow the device  8  to function in accordance with the techniques discussed herein. Those of ordinary skill in the art will appreciate that the various functional blocks shown in  FIG. 1  may comprise hardware elements (including circuitry), software elements (including computer code stored on a computer-readable medium) or a combination of both hardware and software elements. It should further be noted that  FIG. 1  is merely one example of a particular implementation and is merely intended to illustrate the types of components that may be present in a device  8 . For example, in the presently illustrated embodiment, these components may include a display  10 , I/O ports  12 , input structures  14 , one or more processors  16 , a memory device  18 , a non-volatile storage  20 , expansion card(s)  22 , a networking device  24 , and a power source  26 . 
     With regard to each of these components, the display  10  may be used to display various images generated by the device  8 . In one embodiment, the display  10  may be a liquid crystal display (LCD). For example, the display  10  may be an LCD employing fringe field switching (FFS), in-plane switching (IPS), or other techniques useful in operating such LCD devices. Additionally, in certain embodiments of the electronic device  8 , the display  10  may be provided in conjunction with a touch-sensitive element, such as a touchscreen, that may be used as part of the control interface for the device  8 . 
     The I/O ports  12  may include ports configured to connect to a variety of external devices, such as a power source, headset or headphones, or other electronic devices (such as handheld devices and/or computers, printers, projectors, external displays, modems, docking stations, and so forth). The I/O ports  12  may support any interface type, such as a universal serial bus (USB) port, a video port, a serial connection port, an IEEE-1394 port, an Ethernet or modem port, and/or an AC/DC power connection port. 
     The input structures  14  may include the various devices, circuitry, and pathways by which user input or feedback is provided to the processor  16 . Such input structures  14  may be configured to control a function of the device  8 , applications running on the device  8 , and/or any interfaces or devices connected to or used by the electronic device  8 . For example, the input structures  14  may allow a user to navigate a displayed user interface or application interface. Examples of the input structures  14  may include buttons, sliders, switches, control pads, keys, knobs, scroll wheels, keyboards, mice, touchpads, and so forth. 
     In certain embodiments, an input structure  14  and display  10  may be provided together, such an in the case of a touchscreen where a touch sensitive mechanism is provided in conjunction with the display  10 . In such embodiments, the user may select or interact with displayed interface elements via the touch sensitive mechanism. In this way, the displayed interface may provide interactive functionality, allowing a user to navigate the displayed interface by touching the display  10 . 
     User interaction with the input structures  14 , such as to interact with a user or application interface displayed on the display  10 , may generate electrical signals indicative of the user input. These input signals may be routed via suitable pathways, such as an input hub or bus, to the processor(s)  16  for further processing. 
     The processor(s)  16  may provide the processing capability to execute the operating system, programs, user and application interfaces, and any other functions of the electronic device  8 . The processor(s)  16  may include one or more microprocessors, such as one or more “general-purpose” microprocessors, one or more special-purpose microprocessors and/or ASICS, or some combination of such processing components. For example, the processor  16  may include one or more reduced instruction set (RISC) processors, as well as graphics processors, video processors, audio processors and/or related chip sets. 
     The instructions or data to be processed by the processor(s)  16  may be stored in a computer-readable medium, such as a memory  18 . Such a memory  18  may be provided as a volatile memory, such as random access memory (RAM), and/or as a non-volatile memory, such as read-only memory (ROM). The memory  18  may store a variety of information and may be used for various purposes. For example, the memory  18  may store firmware for the electronic device  8  (such as a basic input/output instruction or operating system instructions), various programs, applications, or routines executed on the electronic device  8 , user interface functions, processor functions, and so forth. In addition, the memory  18  may be used for buffering or caching during operation of the electronic device  8 . 
     The components may further include other forms of computer-readable media, such as a non-volatile storage  20 , for persistent storage of data and/or instructions. The non-volatile storage  20  may include flash memory, a hard drive, or any other optical, magnetic, and/or solid-state storage media. The non-volatile storage  20  may be used to store firmware, data files, software, wireless connection information, and any other suitable data. 
     The embodiment illustrated in  FIG. 1  may also include one or more card or expansion slots. The card slots may be configured to receive an expansion card  22  that may be used to add functionality, such as additional memory, I/O functionality, or networking capability, to the electronic device  8 . Such an expansion card  22  may connect to the device through any type of suitable connector, and may be accessed internally or external to the housing of the electronic device  8 . For example, in one embodiment, the expansion card  22  may be a flash memory card, such as a SecureDigital (SD) card, mini- or microSD, CompactFlash card, Multimedia card (MMC), or the like. 
     The components depicted in  FIG. 1  also include a network device  24 , such as a network controller or a network interface card (NIC). In one embodiment, the network device  24  may be a wireless NIC providing wireless connectivity over any  802 . 11  standard or any other suitable wireless networking standard. The network device  24  may allow the electronic device  8  to communicate over a network, such as a Local Area Network (LAN), Wide Area Network (WAN), or the Internet. Further, the electronic device  8  may connect to and send or receive data with any device on the network, such as portable electronic devices, personal computers, printers, and so forth. Alternatively, in some embodiments, the electronic device  8  may not include a network device  24 . In such an embodiment, a NIC may be added as an expansion card  22  to provide similar networking capability as described above. 
     Further, the components may also include a power source  26 . In one embodiment, the power source  26  may be one or more batteries, such as a lithium-ion polymer battery or other type of suitable battery. The battery may be user-removable or may be secured within the housing of the electronic device  8 , and may be rechargeable. Additionally, the power source  26  may include AC power, such as provided by an electrical outlet, and the electronic device  8  may be connected to the power source  26  via a power adapter. This power adapter may also be used to recharge one or more batteries if present. 
     With the foregoing in mind,  FIG. 2  illustrates an electronic device  8  in the form of a handheld device  30 , here a cellular telephone. It should be noted that while the depicted handheld device  30  is provided in the context of a cellular telephone, other types of handheld devices (such as media players for playing music and/or video, personal data organizers, handheld game platforms, and/or combinations of such devices) may also be suitably provided as the electronic device  8 . Further, a suitable handheld device  30  may incorporate the functionality of one or more types of devices, such as a media player, a cellular phone, a gaming platform, a personal data organizer, and so forth. 
     For example, in the depicted embodiment, the handheld device  30  is in the form of a cellular telephone that may provide various additional functionalities (such as the ability to take pictures, record audio and/or video, listen to music, play games, and so forth). As discussed with respect to the general electronic device of  FIG. 1 , the handheld device  30  may allow a user to connect to and communicate through the Internet or through other networks, such as local or wide area networks. The handheld electronic device  30 , may also communicate with other devices using short-range connections, such as Bluetooth and near field communication. By way of example, the handheld device  30  may be a model of an iPod® or iPhone® available from Apple Inc. of Cupertino, Calif. 
     In the depicted embodiment, the handheld device  30  includes an enclosure or body that protects the interior components from physical damage and shields them from electromagnetic interference. The enclosure may be formed from any suitable material such as plastic, metal or a composite material and may allow certain frequencies of electromagnetic radiation to pass through to wireless communication circuitry within the handheld device  30  to facilitate wireless communication. 
     In the depicted embodiment, the enclosure includes user input structures  14  through which a user may interface with the device. Each user input structure  14  may be configured to help control a device function when actuated. For example, in a cellular telephone implementation, one or more of the input structures  14  may be configured to invoke a “home” screen or menu to be displayed, to toggle between a sleep and a wake mode, to silence a ringer for a cell phone application, to increase or decrease a volume output, and so forth. 
     In the depicted embodiment, the handheld device  30  includes a display  10  in the form of an LCD  32 . The LCD  32  may be used to display a graphical user interface (GUI)  34  that allows a user to interact with the handheld device  30 . The GUI  34  may include various layers, windows, screens, templates, or other graphical elements that may be displayed in all, or a portion, of the LCD  32 . Generally, the GUI  34  may include graphical elements that represent applications and functions of the electronic device. The graphical elements may include icons  36  and other images representing buttons, sliders, menu bars, and the like. The icons  36  may correspond to various applications of the electronic device that may open upon selection of a respective icon  36 . Furthermore, selection of an icon  36  may lead to a hierarchical navigation process, such that selection of an icon  36  leads to a screen that includes one or more additional icons or other GUI elements. The icons  36  may be selected via a touchscreen included in the display  10 , or may be selected by a user input structure  14 , such as a wheel or button. 
     The handheld electronic device  30  also may include various input and output (I/O) ports  12  that allow connection of the handheld device  30  to external devices. For example, one I/O port  12  may be a port that allows the transmission and reception of data or commands between the handheld electronic device  30  and another electronic device, such as a computer. Such an I/O port  12  may be a proprietary port from Apple Inc. or may be an open standard I/O port. 
     In addition to handheld devices  30 , such as the depicted cellular telephone of  FIG. 2 , an electronic device  8  may also take the form of a computer or other type of electronic device. Such computers may include computers that are generally portable (such as laptop, notebook, and tablet computers) as well as computers that are generally used in one place (such as conventional desktop computers, workstations and/or servers). In certain embodiments, the electronic device  8  in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. By way of example, an electronic device  8  in the form of a laptop computer  50  is illustrated in  FIG. 3  in accordance with one embodiment of the present invention. The depicted computer  50  includes a housing  52 , a display  10  (such as the depicted LCD  32 ), input structures  14 , and input/output ports  12 . 
     In one embodiment, the input structures  14  (such as a keyboard and/or touchpad) may be used to interact with the computer  50 , such as to start, control, or operate a GUI or applications running on the computer  50 . For example, a keyboard and/or touchpad may allow a user to navigate a user interface or application interface displayed on the LCD  32 . 
     As depicted, the electronic device  8  in the form of computer  50  may also include various input and output ports  12  to allow connection of additional devices. For example, the computer  50  may include an I/O port  12 , such as a USB port or other port, suitable for connecting to another electronic device, a projector, a supplemental display, and so forth. In addition, the computer  50  may include network connectivity, memory, and storage capabilities, as described with respect to  FIG. 1 . As a result, the computer  50  may store and execute a GUI and other applications. 
     With the foregoing discussion in mind, it may be appreciated that an electronic device  8  in the form of either a handheld device  30  or a computer  50  may be provided with an LCD  32  as the display  10 . Such an LCD  32  may be utilized to display the respective operating system and application interfaces running on the electronic device  8  and/or to display data, images, or other visual outputs associated with an operation of the electronic device  8 . 
     In embodiments in which the electronic device  8  includes an LCD  32 , the LCD  32  may include an array or matrix of picture elements (i.e., pixels). In operation, the LCD  32  generally operates to modulate the transmission of light through the pixels by controlling the orientation of liquid crystal disposed at each pixel. In general, the orientation of the liquid crystals is controlled by a varying an electric field associated with each respective pixel, with the liquid crystals being oriented at any given instant by the properties (strength, shape, and so forth) of the electric field. 
     Different types of LCDs may employ different techniques in manipulating these electrical fields and/or the liquid crystals. For example, certain LCDs employ transverse electric field modes in which the liquid crystals are oriented by applying an in-plane electrical field to a layer of the liquid crystals. Example of such techniques include in-plane switching (IPS) and fringe field switching (FFS) techniques, which differ in the electrode arrangement employed to generate the respective electrical fields. 
     While control of the orientation of the liquid crystals in such displays may be sufficient to modulate the amount of light emitted by a pixel, color filters may also be associated with the pixels to allow specific colors of light to be emitted by each pixel. For example, in embodiments where the LCD  32  is a color display, each pixel of a group of pixels may correspond to a different primary color. For example, in one embodiment, a group of pixels may include a red pixel, a green pixel, and a blue pixel, each associated with an appropriately colored filter. The intensity of light allowed to pass through each pixel (by modulation of the corresponding liquid crystals), and its combination with the light emitted from other adjacent pixels, determines what color(s) are perceived by a user viewing the display. As the viewable colors are formed from individual color components (e.g., red, green, and blue) provided by the colored pixels, the colored pixels may also be referred to as unit pixels. 
     With the foregoing in mind, and turning once again to the figures,  FIG. 4  depicts an exploded view of different layers of a pixel of an LCD  32 . The pixel  60  includes an upper polarizing layer  64  and a lower polarizing layer  66  that polarize light emitted by a backlight assembly  68  or light-reflective surface. A lower substrate  72  is disposed above the polarizing layer  66  and is generally formed from a light-transparent material, such as glass, quartz, and/or plastic. 
     A thin film transistor (TFT) layer  74  is depicted as being disposed above the lower substrate  72 . For simplicity, the TFT layer  74  is depicted as a generalized structure in  FIG. 4 . In practice, the TFT layer may itself comprise various conductive, non-conductive, and semiconductive layers and structures which generally form the electrical devices and pathways which drive operation of the pixel  60 . For example, in an embodiment in which the pixel  60  is part of an FFS LCD panel, the TFT layer  74  may include the respective data lines, scanning or gate lines, pixel electrodes, and common electrodes (as well as other conductive traces and structures) of the pixel  60 . Such conductive structures may, in light-transmissive portions of the pixel, be formed using transparent conductive materials, such as indium tin oxide (ITO). In addition, the TFT layer  74  may include insulating layers (such as a gate insulating film) formed from suitable transparent materials (such as silicon oxide) and semiconductive layers formed from suitable semiconductor materials (such as amorphous silicon). In general, the respective conductive structures and traces, insulating structures, and semiconductor structures may be suitably disposed to form the respective pixel and common electrodes, a TFT, and the respective data and scanning lines used to operate the pixel  60 , as described in further detail below with regard to  FIG. 5 . The TFT layer  74  may also include an alignment layer (formed from polyimide or other suitable materials) at the interface with the liquid crystal layer  78 . 
     The liquid crystal layer  78  includes liquid crystal particles or molecules suspended in a fluid or gel matrix. The liquid crystal particles may be oriented or aligned with respect to an electrical field generated by the TFT layer  74 . The orientation of the liquid crystal particles in the liquid crystal layer  78  determines the amount of light transmission through the pixel  60 . Thus, by modulation of the electrical field applied to the liquid crystal layer  78 , the amount of light transmitted though the pixel  60  may be correspondingly modulated. 
     Disposed on the other side of the liquid crystal layer  78  from the TFT layer  74  may be one or more alignment and/or overcoating layers  82  interfacing between the liquid crystal layer  78  and an overlying color filter  86 . The color filter  86 , in certain embodiments, may be a red, green, or blue filter, such that each pixel  60  corresponds to a primary color when light is transmitted from the backlight assembly  68  through the liquid crystal layer  78  and the color filter  86 . 
     The color filter  86  may be surrounded by a light-opaque mask or matrix, e.g., a black mask  88  which circumscribes the light-transmissive portion of the pixel  60 . For example, in certain embodiments, the black mask  88  may be sized and shaped to define a light-transmissive aperture over the liquid crystal layer  78  and around the color filter  86  and to cover or mask portions of the pixel  60  that do not transmit light, such as the scanning line and data line driving circuitry, the TFT, and the periphery of the pixel  60 . In the depicted embodiment, an upper substrate  92  may be disposed between the black mask  88  and color filter  86  and the polarizing layer  64 . In such an embodiment, the upper substrate may be formed from light-transmissive glass, quartz, and/or plastic. 
     Referring now to  FIG. 5 , an example of a circuit view of pixel driving circuitry found in an LCD  32  is provided. For example, such circuitry as depicted in  FIG. 5  may be embodied in the TFT layer  74  described with respect to  FIG. 4 . As depicted, the pixels  60  may be disposed in a matrix that forms an image display region of an LCD  32 . In such a matrix, each pixel  60  may be defined by the intersection of data lines  100  and scanning or gate lines  102 . 
     Each pixel  60  includes a pixel electrode  110  and thin film transistor (TFT)  112  for switching the pixel electrode  110 . In the depicted embodiment, the source  114  of each TFT  112  is electrically connected to a data line  100 , extending from respective data line driving circuitry  120 . Similarly, in the depicted embodiment, the gate  122  of each TFT  112  is electrically connected to a scanning or gate line  102 , extending from respective scanning line driving circuitry  124 . In the depicted embodiment, the pixel electrode  110  is electrically connected to a drain  128  of the respective TFT  112 . 
     In one embodiment, the data line driving circuitry  120  sends image signals to the pixels via the respective data lines  100 . Such image signals may be applied by line-sequence, i.e., the data lines  100  may be sequentially activated during operation. The scanning lines  102  may apply scanning signals from the scanning line driving circuitry  124  to the gate  122  of each TFT  112  to which the respective scanning lines  102  connect. Such scanning signals may be applied by line-sequence with a predetermined timing and/or in a pulsed manner. 
     Each TFT  112  serves as a switching element which may be activated and deactivated (i.e., turned on and off) for a predetermined period based on the respective presence or absence of a scanning signal at the gate  122  of the TFT  112 . When activated, a TFT  112  may store the image signals received via a respective data line  100  as a charge in the pixel electrode  110  with a predetermined timing. 
     The image signals stored at the pixel electrode  110  may be used to generate an electrical field between the respective pixel electrode  110  and a common electrode. Such an electrical field may align liquid crystals within the liquid crystal layer  78  ( FIG. 4 ) to modulate light transmission through the liquid crystal layer  78 . In some embodiments, a storage capacitor may also be provided in parallel to the liquid crystal capacitor formed between the pixel electrode  110  and the common electrode to prevent leakage of the stored image signal at the pixel electrode  110 . For example, such a storage capacitor may be provided between the drain  128  of the respective TFT  112  and a separate capacitor line. 
     Various partial cross-sections of pixels of certain LCD panel embodiments are provided in  FIGS. 6-12  and discussed in greater detail below. Beginning with  FIG. 6 , a partial cross-section of a pixel  140  is provided in accordance with one embodiment. Although the pixel  140  is illustrated in accordance with a fringe field switching (FFS) LCD panel, the use of the presently disclosed techniques with other display technologies is also envisaged. As generally described above with reference to  FIG. 4 , the pixel  140  may include a lower substrate  72  and a control layer, such as a TFT layer  74 , disposed over the lower substrate  72  and capable of generating and varying electric fields to control orientation of liquid crystals within the pixel  140 . 
     In the illustrated embodiment, the TFT layer  74  includes a gate insulation layer  142  disposed over and in contact with the lower substrate  72 , electrode layers  144  and  146  disposed over the gate insulation layer  142  and the substrate  72 , and a passivation layer  148  disposed between the respective electrode layers  144  and  146 . The gate insulation layer  142  may be an oxide layer disposed over and in contact with the substrate  72 , and both the substrate  72  and the gate insulation layer  142  may, in at least some embodiments, have refractive indices of approximately 1.5. As will be appreciated by those skilled in the art, the gate insulation layer  142  may be disposed over gates  122  of TFTs  112  ( FIG. 5 ) formed on the substrate  72  to insulate the gates  122  from other conductive structures of the TFTs  112 . 
     The electrode layers  144  and  146  may be formed of any suitable material, such as ITO, which may have a refractive index of approximately 1.8. In one embodiment, the electrode layer  144  may be a common electrode shared by multiple pixels of the display panel, and the electrode layer  146  may be a pixel electrode having a number of elongated portions spaced apart from one another within the pixel  140 . It is noted, however, that in other embodiments the electrode layer  144  may be a pixel electrode and the electrode layer  146  may be a common electrode. The passivation layer  148  electrically isolates the electrode layers  144  and  146  from one another, and may also be formed of any suitable material. For instance, in some embodiments, the passivation layer  148  is a silicon nitride film, and may have a refractive index of approximately 2.0. 
     Although in other embodiments the electrode layer  144  may be disposed in contact with the gate insulation layer  142 , and the passivation layer  148  may be disposed in contact with either or both of the electrode layers  144  and  146 , in the presently illustrated embodiment the pixel  140  includes index-matching layers  150 ,  152 , and  154  that are interposed between these layers. Particularly, such index-matching layers may include intermediate passivation layers provided between other layers of the pixel  140  having different refractive indices, and these index-matching layers may have a refractive index between those of the adjoining layers to reduce internal reflectance within the pixel  140 , as described in greater detail below. 
     As generally indicated by reference numeral  160 , light incident on the substrate  72  may be transmitted through the various layers of the display stack illustrated in  FIG. 6 . As this light passes through the various media of the pixel  140 , a portion of the light is reflected at each interface between layers having different refractive indices, as generally represented at reference numerals  162 . As a result, and as generally represented by reference numeral  164 , the amount of light successfully transmitted through all of the layers of the substrate  72  and the TFT layer  74 , and into a liquid crystal layer  78  ( FIG. 4 ), is only a portion of the light incident on the lower substrate  72 . It will be further appreciated that additional reflective losses may occur at additional interfaces within the pixel  140 , such as at interfaces between various other layers described above with respect to  FIG. 4 . 
     It is noted that the addition of index-matching layers to the display stack of pixel  140  may generally increase the number of interfaces (and reflections) between materials having different refractive indices. Such index-matching layers, however, reduce the magnitude of reflection at each interface by such a degree that the aggregate amount of light reflected at the upper and lower surfaces of an index-matching layer is less, and in some cases substantially less (e.g., forty-five to approximately fifty percent), than that which would be reflected at a single interface between the layers on opposite sides of the index-matching layer. 
     By way of further example, different exemplary arrangements of several layers of the pixel  140  are illustrated in  FIGS. 7 and 8 . In the embodiment illustrated in  FIG. 7 , in which index-matching layers are omitted, light  170  passing through the lower substrate  72  propagates through the gate insulation layer  142 , the electrode layer  144 , and into the passivation layer  148 . In the embodiment of  FIG. 8 , however, index-matching layer  150  is disposed between the gate insulation layer  142  and the electrode layer  144 , while index-matching layer  152  is interposed between the electrode layer  144  and the passivation layer  148 . Although other layers of the pixel  140  have been omitted for the sake of clarity, it will be appreciated that the light entering the passivation layer  148  may, in turn, pass through a number of other layers, such as those described above, before exiting the pixel  140 . 
     In one embodiment, the substrate  72  and the gate insulation layer  142  may have substantially identical refractive indices of approximately 1.5, the electrode layer  144  may have a refractive index of approximately 1.8, and the passivation layer  148  may have a refractive index of approximately 2.0. For light normal to an interface between materials of different refractive indices, the component of the light that is reflected at such an interface may be generally represented as: 
                   R   =       [         n   2     -     n   1           n   2     +     n   1         ]     2             (   1   )               
where R is the ratio of reflected light to incident light, and n 1  and n 2  are the refractive indices of the materials the light is passing from and into, respectively, at the interface.
 
     In both the embodiments of  FIGS. 7 and 8 , because the lower substrate  72  and the gate insulation  142  have substantially identical refractive indices, the light  170  traveling through the substrate  72  may pass through an interface  172  between such layers with virtually no reflection. In the embodiment of  FIG. 7 , the light  170  then passes through the gate insulation  142  to an interface  174  between the gate insulation layer  142  and the electrode layer  144 . Given Equation 1 above, and that the refractive indices of the gate insulation layer  142  and the electrode layer  144  are approximately 1.5 and 1.8 respectively, it can be calculated that approximately 0.83 percent of the light normal to the interface  174  will be reflected, as generally indicated by reference numeral  176 , with the remaining light passing into the electrode layer  144 . 
     In turn, as the light reaches interface  178  between the electrode layer  144  (n˜1.8) and the passivation layer  148  (n˜2.0), approximately 0.28 percent of the light normal to the interface  178  will be reflected back into the electrode layer  144 , as generally represented by reference numeral  180 , rather than transmitted into the passivation layer  148 . Thus, the total amount of light passing into the passivation layer  148 , generally represented by reference numeral  182 , may be approximately 1.1 percent less than the amount of light  170  that entered the substrate  72 . While the amount of light reflected at any one interface may be relatively small, it will be appreciated that the aggregate transmittance losses due to internal reflectance between the many layers of the pixel  140  may noticeably reduce the brightness of the pixel  140 . 
     In sharp contrast, the index-matching layers  150  and  152  in  FIG. 8  may reduce the reflective losses resulting from the passage of light from the substrate  72  into the passivation layer  148 . In various embodiments, the refractive index of the index-matching layer  150  is greater than the refractive index of approximately 1.5 of the gate insulation layer  142 , and is less than the refractive index of approximately 1.8 of the electrode layer  144 . In one embodiment, the index-matching layer  150 , as well as any or all other index-matching layers, may have a refractive index that is approximately the square root of the product of the refractive indices of the layers on opposing sides of the index-matching layer. Consequently, in one embodiment, the index-matching layer  150  may have a refractive index of approximately 1.64 (i.e., approximately the square root of the product of 1.5 and 1.8). The index-matching layer  150  may be formed of any suitable material, such as that available from JSR Corporation of Tokyo, Japan, as product number KZ6676. 
     In this embodiment, the index-matching layer  150  may form interfaces  188  and  190  along the gate insulation layer  142  and the electrode layer  144 , respectively. Given Equation 1 above, it can be calculated that approximately 0.21 percent of the light passing through the gate insulation layer  142  along the normal of the interface  188  may be reflected at the interface  188  (generally indicated by reference numeral  196 ), and approximately 0.21 percent of the light passing similarly through the interface  190  may also be reflected (generally indicated by reference numeral  198 ). 
     Further, in an embodiment in which the passivation layer  148  has a refractive index of approximately 2.0, the index-matching layer  152  may have a refractive index of approximately 1.90, which is approximately the square root of the product of the refractive indices of the electrode layer  144  and the passivation layer  148 . In this embodiment, the reflective losses of light normal to the interfaces  192  and  194  may be calculated to be approximately 0.07 percent each, and are generally indicated by reference numerals  200  and  202 . Consequently, the amount of reflective losses from propagation of light from the substrate  72  into the passivation layer  148  in the embodiment of  FIG. 8  is only approximately 0.56 percent, leading to a greater amount of light  204  reaching the passivation layer  148  when compared to the embodiment of  FIG. 7 . It may be observed that although the embodiment of  FIG. 8  includes a greater number of interfaces from which light is reflected, the aggregate reflective losses through the illustrated layers of  FIG. 8  are only approximately half that of the corresponding layers in  FIG. 7 . 
     Although  FIG. 8  depicts two index-matching layers disposed between three other layers having different refractive indices, it will be appreciated that various index-matching layers may be added or omitted as desired in other embodiments. For example, as illustrated in  FIG. 9 , the index-matching layer  152  between the electrode layer  144  and the passivation layer  148  may be omitted. In this example, light  170  would be reflected at the sequential interfaces  188 ,  190 , and  178  by the amounts generally discussed above with respect to  FIGS. 7 and 8 , resulting in an amount of light  210  reaching the passivation layer  148 . 
     Although each index-matching layer  150 ,  152 , and  154  is illustrated as a single layer for explanatory purposes, it is noted that these index-matching layers, as well as other such layers, may be provided as a plurality of index-matching layers. For example, the index-matching layer  150  could be provided as two or more index-matching layers having different refractive indices than both each other and the adjoining layers. In one embodiment, multiple contiguous index-matching layers may have refractive indices such that the refractive index of each layer is the square root of the product of the refractive indices of the adjoining layers. 
     The passage of light through the passivation layer  148  and the electrode layer  146  of one embodiment of the pixel  140  is generally depicted in  FIG. 10 . In the presently illustrated embodiment, light  216  transmitted through the passivation layer  148  may pass through the index-matching layer  154  and the electrode layer  146  before reaching the liquid crystal layer  78 . As noted above, in some embodiments the passivation layer  148  may have a refractive index of approximately 2.0. Additionally, in one embodiment the electrode layer  146  and the liquid crystal layer  78  may have refractive indices of approximately 1.8 and 1.5, respectively. As the light  216  passes through the layers illustrated in  FIG. 10 , light may be reflected at interfaces  218 ,  220 , and  222  as a result of the differences in refractive indices of the materials of the layers (as generally represented by reference numerals  224 ,  226 , and  228 , respectively), and a remaining portion of light  230  may pass into the liquid crystal layer  78 . In one embodiment, the index-matching layer may have a refractive index between those of the passivation layer  148  and the electrode layer  146 , such as approximately 1.90 (i.e., approximately the square root of the product of the refractive indices of the passivation layer  148  and the electrode layer  146 ). In another embodiment, an additional index-matching layer may be provided between the electrode layer  146  and the liquid crystal layer  78  to reduce reflectance of light passing between these layers. 
     It is noted, however, that in some embodiments of an IPS or FFS LCD panel a series of electrode portions (e.g., the electrode layer  146 ) may be separated from one another along a surface of the index-matching layer  154 , such that the index-matching layer  154  contacts the electrode layer  146  only along portions of the interface  220 , while other portions of the index-matching layer  154  may contact the liquid crystal layer  78 . Light  234  passing from the passivation layer  148  may generally propagate through the index-matching layer  154  and into the liquid crystal layer  78 , without passing through the electrode layer  146 . In such an embodiment, reflective losses for light  234  passing from the passivation layer  148  into the liquid crystal layer  78  may occur only at interfaces  218  and  220 , as generally indicated by reference numerals  236  and  238 , and the remaining light may pass into the liquid crystal layer  78 , as generally represented by reference numeral  240 . 
     Accordingly, in other embodiments, the index-matching layer  154  may have a refractive index between those of the passivation layer  148  and the liquid crystal layer  78 , and less than that of the electrode layer  146 . For example, in one embodiment, the index-matching layer  154  may have a refractive index of approximately 1.74 (i.e., approximately equal to the square root of the product of 1.5 and 2.0). As with the other index-matching layers described herein, the index-matching layer  154  may be formed of any suitable material, such as that available from JSR Corporation of Tokyo, Japan, as product number TT8038. 
     In another embodiment, the index-matching layer  154  may include multiple regions having different refractive indices, as generally depicted in  FIG. 11 . In this presently illustrated embodiment, portions  246  of the index-matching layer  154  having a first refractive index may be provided at regions directly between the passivation layer  148  and the electrode layer  146 . Additional portions  248  of the index-matching layer  154  having a second refractive index may be provided at positions directly between the passivation layer  148  and the liquid crystal layer  78 . In such an embodiment, the different refractive indices of the portions  246  and  248  may be independently selected to reduce reflectance across the relevant layers. For example, in one embodiment, the portions  246  may have a refractive index of approximately 1.90, while the portions  248  may have a refractive index of approximately 1.74. 
     As light  216  generally propagates from the passivation layer  148 , some of the light is reflected at the interface  218 , at a region  250  of the interface  220  between the portion  246  of the index-matching layer  154  and the electrode layer  146 , and at the interface  222 . These reflective losses are generally indicated as reference numerals  254 ,  256 , and  258 , respectively, and a remaining portion  260  of light passes into the liquid crystal layer  78 . Additional light  234  may pass through the passivation layer  148 , a portion  248  of the index-matching layer  154 , and into the liquid crystal layer  78 . The light  234  is partially reflected at interface  218  and a region  252  of the interface  220 , as generally represented by reference numerals  266  and  268 , and the remaining light passes through the liquid crystal layer  78 , as generally indicated by reference numeral  270 . 
     Although certain layers of display pixels have been described above, it is noted that pixels and displays of other embodiments may include fewer layers, and may include more layers in addition to, or in place of, those described above. For example, an embodiment of a pixel  274  having a greater number of layers than the pixel  140  is generally illustrated in  FIG. 12  in full accordance with the present techniques. The pixel  274  may include a lower substrate  72  and a TFT layer  74 . As noted above, the lower substrate  72  may be a transparent material, such as glass, and may have a refractive index of approximately 1.5. 
     The TFT layer  74 , in turn, may include a gate insulation layer  276 , and electrode layers  278  and  280  generally disposed about a passivation layer  282 . As in the examples described above, the gate insulation layer  276  may include an oxide layer having a refractive index substantially similar to that of the lower substrate  72 , such as approximately 1.5, although other gate insulation layers  276  having different refractive indices may also be used. The electrode layers  278  and  280  may be formed of any suitable material, such as ITO having a refractive index of approximately 1.8. The passivation layer  282  may, in one embodiment, include a silicon nitride film having a refractive index of approximately 2.0. Index-matching layers  284  and  286  may be disposed between the passivation layer  282  and the respective electrode layers  280  and  282 . Additional layers may include a passivation layer  288 , which in one embodiment may be formed of a silicon nitride film with a refractive index of approximately 2.0, and an organic passivation layer  292  having a refractive index of approximately 1.5. Further index-matching layers  290 ,  294 , and  296  may also be provided as generally illustrated in  FIG. 12 . 
     In some embodiments, any or all of the various index-matching layers of the pixel  274  may have a refractive index between those of layers in contact with opposite sides of the respective index-matching layer. In such an embodiment, light  298  passing through the various layers may be reflected (as generally indicated by reference numeral  300 ) by a reduced amount, and a remaining amount of light  302  may pass into the liquid crystal layer  78  above the TFT layer  74 . As generally noted previously, the index-matching layers of one embodiment may be formed of materials having refractive indices approximately equal to the square root of the product of the refractive indices of the layers in contact with opposite sides of the respective index-matching layer to further reduce reflective losses through the TFT layer  74 . 
     While the preceding examples describe configurations of pixels for use in a FFS LCD device, it should be understood that these examples are not intended to be limiting in scope and, indeed, the present teachings may also be applicable to other types of LCDs or display panels, such as IPS LCDs or others. More generally, while the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.

Metadata:
Filing Date: 20090213
Publication Date: 20131015
Grant Date: 20131015
Priority Date: 20090213
Inventors: CHEN CHENG
GU MINGXIA
CHANG SHIH CHANG
ZHONG JOHN Z.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/1362", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133502", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133502", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/1362", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 42559593