PATENT DOCUMENT

Publication Number: US-8441643-B2
Application Number: US-83543110-A
Country: US
Kind Code: B2

Title: Manufacturing and testing techniques for electronic displays

Abstract:
A method for testing photosensitivity of an electronic display module, such as a liquid crystal display module, is provided. In one embodiment, a method includes exposing a display module to light at a first intensity and measuring an amount of light transmitted through the display module. The method may also include exposing the display module to light at a second intensity and measuring an amount of that light transmitted through the display module. The measured amounts may then be compared to determine an optical property, such as photosensitivity, of the display panel. Various other methods, systems, and manufactures are also disclosed.

Claims:
What is claimed is: 
     
       1. A method comprising:
 transmitting light at a first luminance level from a backlight unit to illuminate a thin-film transistor liquid crystal display module produced by a manufacturing process, the thin-film transistor liquid crystal display module including a plurality of pixels and circuitry to control the amount of light permitted through the plurality of pixels; 
 operating the plurality of pixels at a plurality of gray scale levels; 
 measuring the transmittance of the thin-film transistor liquid crystal display module illuminated at the first luminance level at each of the plurality of gray scale levels; 
 transmitting light at a second luminance level from a backlight unit to illuminate the thin-film transistor liquid crystal display module; 
 operating the plurality of pixels at the plurality of gray scale levels; 
 measuring the transmittance of the thin-film transistor liquid crystal display module illuminated at the second luminance level at each of the plurality of gray scale levels; 
 identifying the photosensitivity of the thin-film transistor liquid crystal display module by determining the difference between transmittance of the thin-film transistor liquid crystal display module illuminated at the first and second luminance levels for each of the gray scale levels; 
 comparing the photosensitivity of the thin-film transistor liquid crystal display module to a sensitivity threshold; and 
 modifying at least one parameter of the manufacturing process based on the comparison. 
 
     
     
       2. The method of  claim 1 , wherein transmitting light at the first luminance level includes transmitting light at approximately the maximum brightness level of a light source to be assembled with the thin-film transistor liquid crystal display module in a housing. 
     
     
       3. The method of  claim 2 , comprising assembling the light source and the thin-film transistor liquid crystal display module in the housing. 
     
     
       4. The method of  claim 2 , wherein transmitting light at the second luminance level includes transmitting light at approximately the minimum brightness level of the light source. 
     
     
       5. A method comprising: exposing a liquid crystal display module including liquid crystal disposed between first and second substrates to light at a first intensity;
 measuring a first amount of the light at the first intensity transmitted through the liquid crystal display module; 
 exposing the liquid crystal display module to light at a second intensity; 
 measuring a second amount of light at the second intensity transmitted through the liquid crystal display module; and 
 comparing the measured first and second amounts of light to determine an optical property of the liquid crystal display module, wherein measuring the first and second amounts of light includes measuring the first and second amounts of light during operation of the liquid crystal display module at a plurality of gray levels. 
 
     
     
       6. The method of  claim 5 , wherein comparing the measured first and second amounts of light comprises comparing the measured first and second amounts of light prior to assembly of the liquid crystal display module with a light source. 
     
     
       7. The method of  claim 6 , comprising assembling the liquid crystal display module with the light source. 
     
     
       8. The method of  claim 7 , wherein assembling the liquid crystal display module with the light source comprises coupling an edge-lit backlight unit to the liquid crystal display module. 
     
     
       9. The method of  claim 5 , wherein comparing the measured first and second amounts of light to determine an optical property includes determining variations between transmittance of the liquid crystal display module when exposed to light at the first intensity and transmittance of the liquid crystal display module when exposed to light at the second intensity. 
     
     
       10. The method of  claim 9 , wherein determining the variations between transmittance of the liquid crystal display module when exposed to light at the respective first and second intensities includes determining the variations between transmittance of the liquid crystal display module when exposed to light at the first and second intensities for the plurality of gray levels. 
     
     
       11. A method comprising:
 backlighting a display panel under two different luminance conditions, the display panel including a thin-film transistor layer having photosensitive active regions; 
 calculating transmittance differences of the display panel between the two different luminance conditions; 
 determining a transmittance parameter from the calculated transmittance differences; and 
 determining whether photosensitivity of the display panel exceeds a maximum desired level by comparing the transmittance parameter to a predetermined transmittance threshold based on the maximum desired level, wherein the transmittance parameter includes a transmittance parameter selected from the group consisting of:
 a maximum transmittance difference determined from transmittance differences calculated over multiple display panel gray levels; and 
 a mean transmittance difference determined from transmittance differences calculated over multiple display panel gray levels. 
 
 
     
     
       12. The method of  claim 11 , wherein the transmittance parameter includes the maximum transmittance difference determined from transmittance differences calculated over multiple display panel gray levels. 
     
     
       13. The method of  claim 11 , wherein the transmittance parameter includes the mean transmittance difference determined from transmittance differences calculated over multiple display panel gray levels. 
     
     
       14. The method of  claim 11 , wherein backlighting the display panel includes backlighting a liquid crystal display panel. 
     
     
       15. A manufacture comprising:
 one or more tangible, computer-readable storage media having application instructions encoded thereon for execution by a processor, the application instructions comprising:
 instructions for receiving transmittance data from a photodetector, the transmittance data including data representative of the transmittance of a liquid crystal display panel at a plurality of gray levels and a plurality of different illumination intensities; 
 instructions for calculating transmittance differences between the different illumination intensities for the plurality of gray levels; and 
 instructions for facilitating comparison of the calculated transmittance differences to one or more additional values indicative of a minimum desired optical performance of the liquid crystal display panel. 
 
 
     
     
       16. The manufacture of  claim 15 , wherein the instructions for facilitating comparison of the calculated transmittance differences to one or more additional values include instructions for determining a representative value from the calculated transmittance differences and comparing the representative value to the one or more additional values. 
     
     
       17. The manufacture of  claim 15 , wherein the one or more additional values are stored within the one or more tangible, computer-readable storage media. 
     
     
       18. The manufacture of  claim 15 , wherein the one or more tangible, computer-readable storage media include at least one of a magnetic storage medium or a solid-state storage medium.

Description:
BACKGROUND 
     1. Technological Field 
     This disclosure relates generally to electronic displays, such as liquid crystal displays. More specifically, the present disclosure relates to the manufacture and testing of such electronic 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 disclosure, 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 disclosure. 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. 
     LCDs typically include an LCD panel having, among other things, a liquid crystal layer disposed between opposing transparent substrates. The amount of light allowed to pass through the LCD panel varies based on the relative orientation of the liquid crystals. One or both substrates may include electrodes to create electric fields that control the orientation of the liquid crystals and, consequently, the amount of light transmitted by the LCD panel. 
     Additional circuitry may also be provided in the LCD panel to facilitate control of the liquid crystals. For example, thin-film transistors (TFTs) and various conductive lines may be formed on an LCD panel substrate along with electrodes during manufacturing. Circuitry of the LCD panel may be formed through a series of semiconductor fabrication processes that form and remove materials from a substrate. As this circuitry controls the orientation of the liquid crystals in the LCD panel, these fabrication processes impact the optical properties of the resulting LCD panel. 
     SUMMARY 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     The present disclosure generally relates to the manufacture of panels of electronic displays and the testing of optical properties of such panels. In one embodiment, the photosensitivity of a display panel is detected by measuring transmittance of pixels of the panel at different pixel voltage levels and at different light source (e.g., a backlight) luminance conditions. For example, gamma data or curves—representative of transmittance levels of pixels at different pixel voltage levels—may be measured for multiple luminance conditions, such as a first “dim” condition and a second “bright” condition. The gamma data may then be compared to determine transmittance differences for the pixels resulting from the different lighting conditions. Such measurements and determinations may be made before assembly of panels with other components of an electronic display (e.g., backlights and housings), and may facilitate a feedback loop for the panel manufacturing process. In other instances, the present techniques may be used to test assembled electronic displays, rather than just the display panel itself. 
     Various refinements of the features noted above may exist in relation to the presently disclosed embodiments. Additional features may also be incorporated in these various embodiments 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 embodiments 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 disclosure without limitation to the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present disclosure 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 perspective view of a computer in accordance with aspects of the present disclosure; 
         FIG. 3  is a perspective view of a handheld electronic device in accordance with aspects of the present disclosure; 
         FIG. 4  is an exploded view of a liquid crystal display (LCD) in accordance with aspects of the present disclosure; 
         FIG. 5  graphically depicts circuitry that may be found in the LCD of 
         FIG. 4  in accordance with aspects of the present disclosure; 
         FIG. 6  is a partial sectional view of an LCD panel of the LCD of  FIG. 4  depicting parasitic capacitances between various conductive components when the LCD panel is not illuminated via a backlight or other light source in accordance with aspects of the present disclosure; 
         FIG. 7  is a partial sectional view of the LCD panel of  FIG. 6  depicting increased parasitic capacitances between the various conductive components resulting from the increased conductivity of an active layer due to illumination of the LCD panel via the backlight or other light source in accordance with aspects of the present disclosure; 
         FIG. 8  is a graph illustrating the difference in leakage current characteristics of a TFT of the LCD panel of  FIG. 4  due to photosensitivity of its active channel in accordance with aspects of the present disclosure; 
         FIG. 9  is a flowchart generally depicting a method for manufacturing an LCD that implements a feedback loop based on measurement of the photosensitivity of an LCD panel in accordance with aspects of the present disclosure; 
         FIG. 10  depicts a testing apparatus to facilitate measurement of optical properties of an LCD module, such as an LCD panel, prior to assembly with a backlight or other components of an LCD in accordance with aspects of the present disclosure; 
         FIG. 11  is a flowchart representative of a process for determining an optical property of an LCD module in accordance with aspects of the present disclosure; 
         FIG. 12  is a flowchart depicting a method for testing an LCD module and modifying a manufacturing process based on the testing in accordance with aspects of the present disclosure; 
         FIG. 13  is a flowchart depicting a method for testing an LCD module, in which at least one transmittance parameter of the LCD module is determined from transmittance differences of the LCD panel when exposed to light of different intensities and compared to a threshold in accordance with aspects of the present disclosure; and 
         FIG. 14  is a graph depicting examples of transmittance differences of several LCD panels at multiple gray scale levels in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. These described embodiments are provided only by way of example, and do not limit the scope of the present disclosure. 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 described below, the articles “a,” “an,” and “the” 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. Additionally, it should be understood that references to “one embodiment,” “an embodiment,” “some embodiments,” and the like are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the disclosed features. 
     As noted above, the present application is generally directed to the manufacturing and testing of optical properties of an electronic display, such as the photosensitivity of such displays resulting from the incorporation of photosensitive materials in the displays. For instance, a TFT-LCD display may include photosensitive active materials, such as amorphous silicon (a-Si), whose conductivity (and mobility) changes in response to light. In some displays, the photosensitive active materials may be used as active channels in TFTs of the displays. Even if these active channels in the TFTs are not directly exposed to light from a backlight unit in operation (e.g., gate material may shield the active channels), these active channels may be indirectly exposed and impacted by light. Additionally, in some LCD manufacturing process, photosensitive active materials may also be disposed beneath data lines formed on a substrate of the display panel. The extent to which the electrical properties of the active materials are impacted depend on the amount of light to which they are exposed and, consequently, on the design and construction of the TFT layer and the fabrication process tolerances. 
     With respect to LCD manufacturing processes, it is noted that the number of processing steps used in a particular manufacturing process impacts the ultimate manufacturing costs for producing LCDs. Such processing steps often include forming and patterning layers of material on substrates of display panels. Patterning of the materials is often accomplished via lithographic techniques that employ resist layers, photo masks, and etchants, applied at and for various times, to form desired structures on the display panels. Typically, reducing the number of steps results in increased production rates and reduced costs. 
     Accordingly, a four-mask manufacturing process (i.e., one that uses four masks in the patterning of the structures of the TFT layer) may be less expensive than a five-mask manufacturing process. In a five-mask process, the active layer of the TFT layer may be formed and patterned using a mask, and various conductive lines (e.g., data lines) and portions of the TFTs (e.g., sources and drains) may then be formed and patterned using a different mask. In contrast, a four-mask process may use a single mask for patterning both the active layer and the above-noted conductive portions (e.g., the data lines, sources, and drains), in which the conductive portions are disposed over the active layer. While this combination may reduce the manufacturing costs associated with displays, it may also increase the photosensitivity of the displays by increasing the amount of the active material (e.g., by including active material underneath the data lines) exposed to light during operation of the display. 
     In some instances, the photosensitivity of the a-Si or other active materials may result in visual artifacts in images output by the display. For example, in a display having a pulse-width modulated (PWM) backlight, optical beating between the horizontal-line frequency of a display (e.g., 40 kHz-60 kHz) and the PWM dimming frequency of the backlight (e.g., 400 Hz-600 Hz) may cause a user to perceive a “shimmering” effect in the displayed images. Further, as the brightness capabilities of LCD backlights increase, the visual artifacts resulting from the photosensitivity may also become more pronounced. 
     To reduce the perception of such visual artifacts, the PWM dimming frequency may be increased beyond the visual perception range of the human eye, such as to a level of about 20 kHz to about 60 kHz. This approach, however, may reduce the power efficiency of the backlight (e.g., of LED drivers) due to the increased PWM switching frequency, may generate acoustic noise, and may lead to other technical challenges. 
     Accordingly, the presently disclosed techniques facilitate measurement and improvement of the intrinsic photosensitivity of electronic displays to reduce visual artifacts in displayed images. As discussed in greater detail below, in one embodiment the transmittance of a display panel may be measured at different magnitudes of light exposure, and the measured transmittances may be compared to one another to determine the photosensitivity of the display panel. Additionally, if the photosensitivity exceeds a desired threshold, manufacturing process changes may be implemented to improve the photosensitivity of the resulting displays. The present techniques may enable better design flexibility and performance, while lowering manufacturing costs. With these foregoing features in mind, a general description of electronic devices including a display that may be manufactured, tested, or both, in accordance with the presently disclosed techniques is provided below. 
     As may be appreciated, electronic devices may include various internal and/or external components which contribute to the function of the device. For instance,  FIG. 1  is a block diagram illustrating components that may be present in one such electronic device  10 . Those of ordinary skill in the art will appreciate that the various functional blocks shown in  FIG. 1  may include hardware elements (including circuitry), software elements (including computer code stored on a computer-readable medium, such as a hard drive or system memory), or a combination of both hardware and software elements.  FIG. 1  is only one example of a particular implementation and is merely intended to illustrate the types of components that may be present in the electronic device  10 . For example, in the presently illustrated embodiment, these components may include a display  12 , input/output (I/O) ports  14 , input structures  16 , one or more processors  18 , one or more memory devices  20 , non-volatile storage  22 , expansion card(s)  24 , networking device  26 , and power source  28 . 
     The display  12  may be used to display various images generated by the electronic device  10 . The display  12  may be any suitable display, such as a liquid crystal display (LCD) or an organic light-emitting diode (OLED) display. Additionally, in certain embodiments of the electronic device  10 , the display  12  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  10 . 
     The I/O ports  14  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  14  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  16  may include the various devices, circuitry, and pathways by which user input or feedback is provided to processor(s)  18 . Such input structures  16  may be configured to control a function of an electronic device  10 , applications running on the device  10 , and/or any interfaces or devices connected to or used by device  10 . For example, input structures  16  may allow a user to navigate a displayed user interface or application interface. Non-limiting examples of input structures  16  include buttons, sliders, switches, control pads, keys, knobs, scroll wheels, keyboards, mice, touchpads, and so forth. Additionally, in certain embodiments, one or more input structures  16  may be provided together with display  12 , such an in the case of a touchscreen, in which a touch sensitive mechanism is provided in conjunction with display  12 . 
     Processors  18  may provide the processing capability to execute the operating system, programs, user and application interfaces, and any other functions of the electronic device  10 . The processors  18  may include one or more microprocessors, such as one or more “general-purpose” microprocessors, one or more special-purpose microprocessors or ASICS, or some combination of such processing components. For example, the processors  18  may include one or more reduced instruction set (RISC) processors, as well as graphics processors, video processors, audio processors, and the like. As will be appreciated, the processors  18  may be communicatively coupled to one or more data buses or chipsets for transferring data and instructions between various components of the electronic device  10 . 
     Programs or instructions executed by processor(s)  18  may be stored in any suitable manufacture that includes one or more tangible, computer-readable media at least collectively storing the executed instructions or routines, such as, but not limited to, the memory devices and storage devices described below. Also, these programs (e.g., an operating system) encoded on such a computer program product may also include instructions that may be executed by the processors  18  to enable device  10  to provide various functionalities, including those described herein. 
     The instructions or data to be processed by the one or more processors  18  may be stored in a computer-readable medium, such as a memory  20 . The memory  20  may include a volatile memory, such as random access memory (RAM), and/or a non-volatile memory, such as read-only memory (ROM). The memory  20  may store a variety of information and may be used for various purposes. For example, the memory  20  may store firmware for electronic device  10  (such as basic input/output system (BIOS)), an operating system, and various other programs, applications, or routines that may be executed on electronic device  10 . In addition, the memory  20  may be used for buffering or caching during operation of the electronic device  10 . 
     The components of the device  10  may further include other forms of computer-readable media, such as non-volatile storage  22  for persistent storage of data and/or instructions. Non-volatile storage  22  may include, for example, flash memory, a hard drive, or any other optical, magnetic, or solid-state storage media. Non-volatile storage  22  may be used to store firmware, data files, software programs, 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 one or more expansion cards  24  that may be used to add functionality, such as additional memory, I/O functionality, or networking capability, to electronic device  10 . Such expansion cards  24  may connect to device  10  through any type of suitable connector, and may be accessed internally or external to the housing of electronic device  10 . For example, in one embodiment, expansion cards  24  may include a flash memory card, such as a SecureDigital (SD) card, mini- or microSD, CompactFlash card, Multimedia card (MMC), or the like. Additionally, expansion cards  24  may include one or more processor(s)  18  of the device  10 , such as a video graphics card having a GPU for facilitating graphical rendering by device  10 . 
     The components depicted in  FIG. 1  also include a network device  26 , such as a network controller or a network interface card (NIC). In one embodiment, the network device  26  may be a wireless NIC providing wireless connectivity over any 802.11 standard or any other suitable wireless networking standard. The device  10  may also include a power source  28 . In one embodiment, the power source  28  may include one or more batteries, such as a lithium-ion polymer battery or other type of suitable battery. Additionally, the power source  28  may include AC power, such as provided by an electrical outlet, and electronic device  10  may be connected to the power source  28  via a power adapter. This power adapter may also be used to recharge one or more batteries of device  10 . 
     The electronic device  10  may take the form of a computer system or some other type of electronic device. Such computers may include computers that are generally portable (such as laptop, notebook, tablet, and handheld computers), as well as computers that are generally used in one place (such as conventional desktop computers, workstations and/or servers). In certain embodiments, electronic device  10  in the form of a computer may include a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, or Mac Pro® available from Apple Inc. of Cupertino, Calif. By way of example, an electronic device  10  in the form of a laptop computer  30  is illustrated in  FIG. 2  in accordance with one embodiment. The depicted computer  30  includes a housing  32 , a display  12  (e.g., in the form of an LCD  34  or some other suitable display), I/O ports  14 , and input structures  16 . 
     The display  12  may be integrated with the computer  30  (e.g., such as the display of the depicted laptop computer) or may be a standalone display that interfaces with the computer  30  using one of the I/O ports  14 , such as via a DisplayPort, Digital Visual Interface (DVI), High-Definition Multimedia Interface (HDMI), or analog (D-sub) interface. For instance, in certain embodiments, such a standalone display  12  may be a model of an Apple Cinema Display®, available from Apple Inc. 
     Although an electronic device  10  is generally depicted in the context of a computer in  FIG. 2 , an electronic device  10  may also take the form of other types of electronic devices. In some embodiments, various electronic devices  10  may include mobile telephones, media players, personal data organizers, handheld game platforms, cameras, and combinations of such devices. For instance, as generally depicted in  FIG. 3 , the device  10  may be provided in the form of handheld electronic device  36  that includes various functionalities (such as the ability to take pictures, make telephone calls, access the Internet, communicate via email, record audio and video, listen to music, play games, and connect to wireless networks). By way of further example, handheld device  36  may be a model of an iPod® or iPhone® available from Apple Inc. 
     Handheld device  36  of the presently illustrated embodiment includes a display  12 , which may be in the form of an LCD  34 . The LCD  34  may display various images generated by the handheld device  36 , such as a graphical user interface (GUI)  38  having one or more icons  40 . The device  36  may also include various I/O ports  14  to facilitate interaction with other devices, and user input structures  16  to facilitate interaction with a user. 
     One example of an LCD display  34  is depicted in  FIG. 4  in accordance with one embodiment. The depicted LCD display  34  includes an LCD panel  42  and a backlight unit  44 , which may be assembled within a frame  46 . As may be appreciated, the LCD panel  42  may include an array of pixels configured to selectively modulate the amount and color of light passing from the backlight unit  44  through the LCD panel  42 . For example, the LCD panel  42  may include a liquid crystal layer, one or more thin film transistor (TFT) layers configured to control orientation of liquid crystals of the liquid crystal layer via an electric field, and polarizing films, which cooperate to enable the LCD panel  42  to control the amount of light emitted by each pixel. Additionally, the LCD panel  42  may include color filters that allow specific colors of light to be emitted from the pixels (e.g., red, green, and blue). 
     The backlight unit  44  includes one or more light sources  48 . Light from the light source  48  is routed through portions of the backlight unit  44  (e.g., a light guide and optical films) and generally emitted toward the LCD panel  42 . In various embodiments, light source  48  may include a cold-cathode fluorescent lamp (CCFL), one or more light emitting diodes (LEDs), or any other suitable source(s) of light. Further, although the LCD  34  is generally depicted as having an edge-lit backlight unit  44 , it is noted that other arrangements may be used (e.g., direct backlighting) in full accordance with the present technique. 
     Referring now to  FIG. 5 , an example of a circuit view of pixel-driving circuitry found in an LCD  34  is provided. For example, the circuitry depicted in  FIG. 5  may be embodied on the LCD panel  42  described above with respect to  FIG. 4 . The pixel-driving circuitry includes an array or matrix  54  of unit pixels  60  that are driven by data (or source) line driving circuitry  56  and scanning (or gate) line driving circuitry  58 . As depicted, the matrix  54  of unit pixels  60  forms an image display region of the LCD  34 . In such a matrix, each unit pixel  60  may be defined by the intersection of data lines  62  and scanning lines  64 , which may also be referred to as source lines  62  and gate lines  64 . The data line driving circuitry  56  may include one or more driver integrated circuits (also referred to as column drivers) for driving the data lines  62 . The scanning line driving circuitry  58  may also include one or more driver integrated circuits (also referred to as row drivers). 
     Each unit pixel  60  includes a pixel electrode  66  and thin film transistor (TFT)  68  for switching the pixel electrode  66 . In the depicted embodiment, the source  70  of each TFT  68  is electrically connected to a data line  62  extending from respective data line driving circuitry  56 , and the drain  72  is electrically connected to the pixel electrode  66 . Similarly, in the depicted embodiment, the gate  74  of each TFT  68  is electrically connected to a scanning line  64  extending from respective scanning line driving circuitry  58 . 
     In one embodiment, column drivers of the data line driving circuitry  56  send image signals to the pixels via the respective data lines  62 . Such image signals may be applied by line-sequence, i.e., the data lines  62  may be sequentially activated during operation. The scanning lines  64  may apply scanning signals from the scanning line driving circuitry  58  to the gate  74  of each TFT  68 . Such scanning signals may be applied by line-sequence with a predetermined timing or in a pulsed manner. 
     Each TFT  68  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 its gate  74 . When activated, a TFT  68  may store the image signals received via a respective data line  62  as a charge in the pixel electrode  66  with a predetermined timing. 
     The image signals stored at the pixel electrode  66  may be used to generate an electrical field between the respective pixel electrode  66  and a common electrode. Such an electrical field may align liquid crystals within a liquid crystal layer to modulate light transmission through the LCD panel  42 . Unit pixels  60  may operate in conjunction with various color filters, such as red, green, and blue filters. In such embodiments, a “pixel” of the display may actually include multiple unit pixels, such as a red unit pixel, a green unit pixel, and a blue unit pixel, each of which may be modulated to increase or decrease the amount of light emitted to enable the display to render numerous colors via additive mixing of the colors. 
     In some embodiments, a storage capacitor may also be provided in parallel to the liquid crystal capacitor formed between the pixel electrode  66  and the common electrode to prevent leakage of the stored image signal at the pixel electrode  66 . For example, such a storage capacitor may be provided between the drain  72  of the respective TFT  68  and a separate capacitor line. 
     As noted above, the optical properties of a LCD panel, such as the LCD panel  42 , may be impacted by exposure to light. By way of example, a partial cross-section of an LCD panel is depicted in  FIGS. 6 and 7  in accordance with one embodiment. Particularly,  FIGS. 6 and 7  generally illustrate differences in parasitic capacitances in such an LCD panel when the panel is not exposed to light (as generally represented by reference number  76 ) and when the panel is exposed to light (as generally represented by reference number  110 ). 
     In the presently illustrated embodiment, the LCD panel includes a layer of liquid crystals  78  disposed between substrates  80  and  82 . The substrates  80  and  82  may include glass substrates, or may be formed of other transparent materials. In one embodiment, gate metal  84  for the TFTs  68  may be formed on the substrate  80 . It is noted that the gate metal  84  may shield active channels of TFTs  68  (which may be formed of amorphous silicon) from light. A gate insulation layer  86  may be formed over the gate metal  84 , and an active layer  88  may be provided on the gate insulation layer  86 . The active layer  88  may be formed of any suitable material, such as amorphous silicon (a-Si). A conductive data line  62  may be formed over the active layer  88 , and an insulation layer  92  may be disposed over the gate insulation layer  86 , the active layer  88 , and the data line  62 . 
     Pixel electrodes  66  may be formed on the insulation layer  92 , and may be formed of any suitable material, such as indium tin oxide (ITO) or indium zinc oxide (IZO). As noted above with reference to  FIG. 5 , data lines  62  may generally cooperate with TFTs  68  to charge the pixel electrodes  66 . The substrate  82  may also include a black matrix layer  96  and a layer of conductive material, such as ITO or IZO, that serves as a common electrode  98  for at least some pixels of the LCD panel. 
     The pixel electrodes  66  and the common electrode  98  are charged to various levels to create electrical fields that manipulate orientation of the liquid crystals  78 . Parasitic capacitances within the LCD panel, however, also impact the orientation of the liquid crystals  78 . Those skilled in the art will appreciate that capacitance is directly proportional to the area of overlap of two conductive surfaces about an insulator, and is inversely proportional to the distance between the conductive surfaces. In the non-illuminated condition of  FIG. 6 , the parasitic capacitance  100  between the data line  62  and the pixel electrode  66  is inversely proportional to the distance  102  by which they are separated. Further, the parasitic capacitance  104  between the data line  62  and the common electrode  98  is generally proportional to the lateral surface area of the data line  62  depicted in  FIG. 6 . 
     In contrast, when the LCD panel is illuminated ( FIG. 7 ), the conductivity and mobility of the active layer  88  increases due to the photoelectric effect. This results in both a larger parasitic capacitance  112  between the combination of the data line  62  and the active layer  88 , and the pixel electrode  66  (as generally represented by the decreased distance  114 ), as well as a larger parasitic capacitance  116  between the data line  62 —active layer  88  combination and the common electrode  98 . These parasitic capacitances may impact the voltage differential between the pixel electrodes  66  and the common electrode  98 , and thus may impact the transmittance of the associated pixels and introduce visual artifacts in images rendered by the LCD panel. 
       FIG. 8  depicts a graph  120  illustrating the impact of the photosensitivity of an LCD panel on the leakage current of TFTs  68  of the panel. Particularly, the graph  120  illustrates the off-leakage current of the TFT  68  (i.e., the leakage current of the TFT  68  when in its “off” state) as a function of the voltage difference between its gate and its source (as provided along axes  122  and  124 , respectively). Curve  126  generally represents the off-leakage current of the TFTs  68  of an LCD panel when not exposed to light, while curve  128  generally represents the off-leakage current for the LCD panel when the panel is exposed to light of a certain luminance. This increase of the off-leakage currents for the TFTs  68  of the LCD panel upon exposure to light may also change the voltage differential between the pixel electrodes  66  and the common electrode  98  and increase the number, magnitude, or both, of visual artifacts perceived by a user. 
     In one embodiment, LCDs may be manufactured in accordance with flowchart  132  as depicted in  FIG. 9 . At block  134 , a TFT layer may be formed on a substrate, such as substrate  80  ( FIG. 6 ), as generally described above. An LCD panel may then be formed at block  136 . For example, forming the LCD panel may include coupling a TFT substrate, such as that formed at block  134 , with an additional substrate (e.g., substrate  82 ) and filling the assembly with liquid crystals  78  between the two substrates. The photosensitivity of the formed panel, and particularly of the active regions of the TFT layer, may be measured at block  138 . As discussed in greater detail below, feedback  140  may be provided and used to modify the manner in which the TFT layer is formed at block  134 . For instance, excessive levels of photosensitivity may indicate that the active layer  88  or some other circuitry of the TFT layer is out of specification and should be adjusted. If the photosensitivity of the LCD panel is within expected tolerances, the LCD panel may be coupled to one or more additional components at block  142 , such as a backlight unit and a housing. In other embodiments, the measurement at block  138  may be performed following the assembly with other components at block  142 , such as for validation purposes. 
     Testing of the photosensitivity or other optical properties of an LCD module may be carried out with a testing system  148 , which is generally depicted in  FIG. 10  in accordance with one embodiment. The system  148  may be installed at a mass production line for manufacturing displays, enabling testing of optical properties of the LCD module before assembly into an LCD and real-time or near real-time process quality control. In other instances, the system  148  may be used for validation purposes (e.g., to ensure that manufactured display modules have acceptable photosensitivity or other optical characteristics). 
     In this depicted embodiment, a LCD module  150  (e.g., the LCD panel  42 ) including a TFT layer and a liquid crystal layer, and a photodetector  152  may be spaced apart at a distance  154 . In one embodiment, the distance  154  may be between about 400 mm and about 500 mm, though other distances  154  may instead be used. The photodetector  152  is generally positioned to receive light emitted through the LCD module  150  to facilitate measurement of transmittance differences of the LCD module  150  when exposed to lights of different intensities. The photodetector  152  may include any suitable device capable of measuring transmittance, such as the PR-650 manufactured by Photo Reasearch Inc. of Chatsworth, Calif.; the BM-5A manufactured by Topcon America Corp. of Paramus, N.J.; other spectroradiometers or charge-coupled devices (CCDs); or any of numerous alternatives. Also, testing of LCD modules  150  with the system  148  may be performed under dark room conditions to reduce potential error in the measurements. 
     In one embodiment, the LCD module  150  may be placed on a moveable stage  156  that facilitates placement of the LCD module  150  with respect to photodetector  152 . Additionally, the stage  156  may include a variable light source that emits light  158  at selected luminances. Light  160  that has passed through the LCD module  150  may be received by the photodetector  152 , which may measure the luminance of the received light  160 . In one embodiment, a lens  162  may be provided to focus the light  160  on a sensor or receiving aperture of the photodetector  152 . 
     A controller  164  may be used to control the components of the system  148  and to receive data from the photodetector  152 . The controller  164  may be a digital controller, such as a computer, including a memory  166  and a processor  168 . The memory  166  (e.g., an optical, magnetic, or solid-state storage medium) may include stored application instructions for performing various functionalities (including those described in the present disclosure), and these instructions may be executed by the processor  168 . The system  148  may vary the intensity of light transmitted from stage  156  (or from some other light source) and determine transmittance differences of the LCD module  150  for the different light intensities to which it is exposed. 
     One example of a process for determining optical properties of the LCD module  150 , such as photosensitivity, is depicted as a flowchart  170  in  FIG. 11  in accordance with one embodiment. The LCD module  150  may be exposed to light at a first luminance level at block  172 . Based on the amount of the light received at the photodetector  152 , at block  174  the transmittance of the LCD module  150  for the light received at block  172  may be determined. The LCD module  150  may then be exposed to light at a different luminance level at block  176 , and the transmittance of the LCD module  150  may be calculated at this level of luminance at block  178 . The luminance levels of blocks  172  and  176  may be set to any desired level. In some embodiments, these luminance levels may be selected to be representative of the maximum and minimum luminance levels that would be provided by a backlight unit of an assembled display. For instance, one of the luminance levels may be set to between about 20 cd/m 2  to about 30 cd/m 2 , and the other luminance level may be set to between about 400 cd/m 2  to about 500 cd/m 2 . The various transmittance differences of the LCD module  150  resulting from the two different light intensities may be compared to determine an optical property (e.g., photosensitivity) of the LCD module  150  at block  180 . 
     In one embodiment, the LCD panel or module  150  may also be tested at various gray scale levels (i.e., pixel voltage levels) of its pixels in accordance with flowchart  190  of  FIG. 12 . First, the LCD module  150  may be illuminated at a first luminance level at block  192 . As noted above, the light may be provided by the stage  156  or some other light source. While such light illuminates the LCD module  150 , the pixels of the LCD module  150  may be operated at multiple gray scale levels at block  194  by applying different voltages to the pixels. For instance, the pixel driving circuitry of the LCD module  150  may be capable of applying sixty-four different voltage levels (or 256 different levels, or some other number of discrete levels) to the pixel electrodes, and the amount of light transmitted through the pixels depends on the voltage level applied to and stored in the pixels. 
     The transmittance characteristics of the LCD module  150  at the first luminance level may be determined for one or more gray levels at block  196 . In some embodiments such measurements may be taken for each gray level that can be produced by the LCD module, but other embodiments may include taking transmittance measurements at a reduced number of gray levels. The number of gray levels for which measurements are taken, and the particular gray levels selected for measurement, may vary according to user preference. 
     At block  198 , the LCD module may be illuminated at a second luminance level different than the first. One of the luminance levels may be comparable to lower levels of luminance capable of being provided by a backlight of an LCD in which the LCD module  150  is intended to be disposed, while the other luminance level may be comparable to higher levels of luminance capable of being provided by the backlight. As noted above, the first luminance level at block  192  may be about 20 cd/m 2  to about 30 cd/m 2  and the second luminance level may be about 400 cd/m 2  to about 500 cd/m 2 , but other luminance levels may be used in full accordance with the present disclosure. For example, the higher luminance level may be more than two, three, five, ten, twelve, fifteen, twenty, thirty, or fifty times greater than the lower luminance level. 
     The pixels of the LCD module  150  may again be operated at the one or more gray levels and the transmittance of the LCD module for these gray levels may be measured, as generally indicated at blocks  200  and  202 , respectively. The photosensitivity of the LCD module  150  may be identified at block  204 , such as by comparing the gamma curves or data obtained at blocks  196  and  202  or, more generally, comparing differences in transmittance for the gray levels at the different light intensities. In some embodiments this sensitivity may be compared to a desired threshold at block  206 . Further, if the photosensitivity of the LCD module  150  exceeds the desired threshold, a manufacturing process for forming the LCD module  150  may be modified at block  208 . For example, if the photosensitivity of the LCD module  150  is higher than a desired level, the TFT layer may be redesigned, processing times for forming and patterning the structures of the TFT layer may be altered (e.g., to change the critical dimensions of the TFT layer), other additional remedial actions may be taken, or some combination of these actions may be performed. 
     Additionally, further testing may be performed in accordance with flowchart  210  provided in  FIG. 13  in accordance with one embodiment. Particularly, at block  212 , a display panel (e.g., the LCD module  150 ) may be exposed to backlighting conditions of different luminances, as generally described above. Transmittance differences of the display panel resulting from the different luminances may be calculated at block  214 . Further, these transmittance differences may be used to determine one or more transmittance parameters at block  216 . 
     For example, in one embodiment, the transmittance differences at block  214  may be calculated for multiple gray levels of the display panel, and the maximum transmittance difference for any of the gray levels may be set as the transmittance parameter at block  216 . In other embodiments, the transmittance differences calculated at block  214  may be used to determine a mean transmittance difference or a median transmittance difference, which also may be set as the transmittance parameter at block  216 . Whether the transmittance parameters include a maximum transmittance difference, a mean transmittance difference, a median transmittance difference, or some other parameter derived from the transmittance differences calculated at block  214 , the transmittance parameters may generally represent the photosensitivity of the display panel and at block  218  it may be determined whether the photosensitivity of the display panel exceeds one or more corresponding thresholds. In other words, at block  218 , a maximum actual transmittance difference of the LCD panel may be compared to a maximum acceptable transmittance difference, a mean actual transmittance difference may be compared to a mean acceptable transmittance difference, and so forth. 
     A graph  230  generally depicting transmittance differences between three different panels (which may be calculated as described above) is generally provided in  FIG. 14  in accordance with one embodiment. In graph  230 , transmittance differences are depicted along the vertical axis  232  for multiple gray scale levels depicted along horizontal axis  234 . In the present depiction, the first curve  236  generally represents transmittance differences between two luminance levels (e.g., high and low) at multiple gray scale levels of an LCD panel produced by a four-mask process. The second curve  238  may generally represent transmittance differences between the same two luminance levels, at the multiple gray scale levels, of an LCD panel also produced by a (different) four-mask process, but exhibiting less photosensitivity and “shimmering” than the LCD panel represented by curve  236 . Further, curve  240  may generally represent transmittance differences between the two luminance levels and multiple gray scale levels of an LCD panel produced by a five-mask process. 
     As may be seen from the graph  230 , the transmittance differences for the LCD panel represented by curve  236  (i.e., the more photosensitive four-mask panel) are significantly higher than the transmittance differences for the LCD panel represented by curve  238  (i.e., the less photosensitive four-mask panel). As a result, a user may perceive the panel represented by curve  236  to have greater visual artifacts than the panel represented by curve  238 . In the present illustration, the curve  236  includes a maximum transmittance difference at data point  242 , the curve  238  includes a smaller maximum transmittance difference at data point  244 , and the curve  240  (representative of the five-mask produced panel) includes a still smaller maximum transmittance difference at data point  246 . 
     If the maximum desired transmittance difference specified by a manufacturer (or a purchaser, or some other user) was 0.5, the manufacturer could determine that the panel represented by curve  238  meets this specification, while the panel represented by curve  236  does not. Further, if the maximum desired transmittance difference specified was 0.4, the manufacturer could determine that neither of the four-mask-produced panels meets this specification and could make changes to the manufacturing processes for one or both panels. As previously noted, the other transmittance difference characteristics (e.g., median or mean transmittance differences) may also or instead be compared to thresholds and to one another for testing purposes. 
     The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Metadata:
Filing Date: 20100713
Publication Date: 20130514
Grant Date: 20130514
Priority Date: 20100713
Inventors: SON MOO KYUNG
YIN VICTOR HAO-EN
ZHONG JOHN Z.
CHEN WEI
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/1309", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/1309", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133606", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 45466696