PATENT DOCUMENT

Publication Number: US-8294850-B2
Application Number: US-41584809-A
Country: US
Kind Code: B2

Title: LCD panel having improved response

Abstract:
A liquid crystal display (LCD) having a liquid crystal layer is provided. In one embodiment, the liquid crystal layer includes a nematic liquid crystal material having liquid crystal molecules in an untwisted state. A chiral dopant is dispersed within the liquid crystal layer and configured to bias the liquid crystal molecules toward a twisted state. Furthermore, a polymer network is disposed among the liquid crystal molecules and configured to bias the liquid crystal molecules toward the untwisted state. Various additional devices and methods are also provided.

Claims:
1. A liquid crystal display (LCD) panel, comprising:
 a liquid crystal layer disposed between two substrates, the liquid crystal layer including:
 a nematic liquid crystal material comprising a plurality of liquid crystal molecules in an untwisted state; 
 a right-handed chiral dopant dispersed within the nematic liquid crystal material and configured to bias the plurality of liquid crystal molecules in a right-handed direction while maintaining the liquid crystal molecules in the untwisted state; and 
 a polymer network disposed among the plurality of liquid crystal molecules and configured to bias the liquid crystal molecules toward the untwisted state. 
 
 
     
     
       2. The LCD panel of  claim 1 , wherein the LCD panel comprises a fringe field switching (FFS) LCD panel. 
     
     
       3. The LCD panel of  claim 1 , wherein the right-handed chiral dopant is less than about 1% of the liquid crystal layer by weight. 
     
     
       4. The LCD panel of  claim 1 , wherein the polymer network is less than about 10% of the liquid crystal layer by weight. 
     
     
       5. The LCD panel of  claim 1 , wherein a ratio of a thickness of the liquid crystal layer between the two substrates to a pitch of the right-handed chiral dopant is less than about 1. 
     
     
       6. The LCD panel of  claim 1 , wherein a ratio of a thickness of the liquid crystal layer between the two substrates to a pitch of the right-handed chiral dopant is between about 0.01 to 0.8. 
     
     
       7. 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 pixel electrode; 
 a common electrode disposed adjacent to a first side of the pixel electrode; and 
 a liquid crystal layer disposed adjacent to a second side of the pixel electrode, the second side being substantially opposite from the first side, wherein the liquid crystal layer comprises a plurality of liquid crystal molecules in an untwisted state; 
 wherein the plurality of liquid crystal molecules are configured to twist in response to an electrical field generated between the pixel electrode and the common electrode, and wherein the liquid crystal layer comprises a chiral dopant configured to bias the plurality of liquid crystal molecules toward a twisted state while permitting the plurality of liquid crystal molecules to remain in the untwisted state until the electrical field is applied. 
 
 
     
     
       8. The electronic device of  claim 7 , wherein the chiral dopant enables reduction of a response time of the LCD at a given driving voltage. 
     
     
       9. The electronic device of  claim 7 , wherein the chiral dopant enables reduction of a driving voltage of the LCD while maintaining a response time of the LCD. 
     
     
       10. The electronic device of  claim 7 , comprising a polymer network disposed within the liquid crystal layer. 
     
     
       11. The electronic device of  claim 10 , wherein the polymer network is configured to reduce a response time of the LCD. 
     
     
       12. A display panel comprising:
 a liquid crystal layer having a thickness and a plurality of liquid crystal molecules configured to transition between an untwisted state that inhibits transmission of light through the display panel and a twisted state that facilitates transmission of light through the display panel, wherein the liquid crystal layer includes an amount of chiral dopant sufficient to bias the liquid crystal molecules toward the twisted state but less than that which would effect rotation of the liquid crystal molecules toward the twisted state in the absence of an electrical field. 
 
     
     
       13. The display panel of  claim 12 , wherein the chiral dopant is less than about 0.20% of the liquid crystal layer by weight. 
     
     
       14. The display panel of  claim 12 , wherein the chiral dopant is between about 0.05% and 0.75% of the liquid crystal layer by weight. 
     
     
       15. The display panel of  claim 12 , wherein a ratio of the thickness to a pitch of the chiral dopant is between about 0.05 and 0.55. 
     
     
       16. A liquid crystal display (LCD) panel comprising:
 a liquid crystal layer having a plurality of liquid crystal molecules configured to transition between an untwisted state that inhibits transmission of light through the LCD panel and a twisted state that facilitates transmission of light through the LCD panel, wherein the liquid crystal layer includes an amount of chiral dopant sufficient to bias the liquid crystal molecules toward the twisted state but less than that which would effect rotation of the liquid crystal molecules toward the twisted state in the absence of an electrical field, and a polymer network configured to bias the liquid crystal molecules toward the untwisted state. 
 
     
     
       17. The LCD panel of  claim 16 , wherein the polymer network is less than about 20% of the liquid crystal layer by weight. 
     
     
       18. The LCD panel of  claim 16 , wherein the polymer network is between about 1% and 15% of the liquid crystal layer by weight. 
     
     
       19. The LCD panel of  claim 16 , wherein the chiral dopant is configured to reduce a response time of the LCD panel. 
     
     
       20. The LCD panel of  claim 16 , wherein the polymer network increases the tolerance of the LCD panel to mechanical distortion. 
     
     
       21. A method of manufacturing a fringe field switching (FFS) liquid crystal display (LCD) panel, the method comprising:
 forming a liquid crystal layer, wherein forming the liquid crystal layer comprises:
 disposing nematic liquid crystal material between a plurality of alignment layers, wherein the nematic liquid crystal material comprises a plurality of liquid crystal molecules in an untwisted state; 
 dispersing an amount of chiral dopant within the nematic liquid crystal material sufficient to bias the plurality of liquid crystal molecules toward a twisted state while maintaining the liquid crystal molecules in the untwisted state, wherein the chiral dopant is configured to reduce a response time of the FFS LCD panel; and 
 forming a polymer network within the liquid crystal layer, wherein the polymer network is also configured to reduce the response time of the FFS LCD panel. 
 
 
     
     
       22. The method of  claim 21 , wherein the chiral dopant is dispersed within the nematic liquid crystal material prior to disposing the nematic liquid crystal material between the plurality of alignment layers. 
     
     
       23. The method of  claim 21 , wherein forming the polymer network comprises dispersing a pre-polymer solution within the liquid crystal layer prior to disposing the nematic liquid crystal material between the plurality of alignment layers. 
     
     
       24. The method of  claim 23 , wherein forming the polymer network comprises polymerizing the pre-polymer solution after dispersing the chiral dopant within the nematic liquid crystal material. 
     
     
       25. The method of  claim 21 , wherein disposing the nematic liquid crystal material between the plurality of alignment layers comprises disposing the nematic liquid crystal material on a first alignment layer and disposing a second alignment layer on the nematic liquid crystal material.

Description:
BACKGROUND 
     1. Technical Field 
     This disclosure 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, the response time of pixels in 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. Response time may be determined using a variety of techniques such as measuring transition time between pixel states. For example, response time may be computed by adding a rotation time to a realignment time. Rotation time corresponds to the transition period of the liquid crystal molecules from an orientation that inhibits light transmission to an orientation that facilitates light transmission. Conversely, realignment time corresponds to the transition period of the liquid crystal molecules from an orientation that facilitates light transmission to an orientation that inhibits light transmission. Response time may be reduced by increasing a driving voltage that induces liquid crystal molecule transition. Unfortunately, increasing driving voltage also increases power consumption, and may reduce battery life in portable electric devices having LCDs. 
     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 reducing response time, decreasing driving voltage and/or increasing transmittance of an LCD. In accordance with the present disclosure, the LCD may include a liquid crystal layer having liquid crystal molecules. A chiral dopant may be dispersed within the liquid crystal layer and configured to bias the liquid crystal molecules toward a twisted state that facilitates light passage through the LCD. Such a configuration may reduce response time and/or decrease driving voltage. Alternatively, the chiral dopant may be configured to bias the liquid crystal molecules toward an untwisted state that inhibits light passage through the LCD. Such a configuration may reduce response time and/or increase transmittance. In addition, a polymer network may be disposed among the liquid crystal molecules and configured to bias the liquid crystal molecules toward the untwisted state, thereby reducing response time of the LCD. The polymer network may be employed alone or in conjunction with the chiral dopant. 
     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 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 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 cutaway cross-sectional side view of an LCD pixel having liquid crystal molecules oriented to inhibit light passage, in accordance with aspects of the present disclosure; 
         FIG. 7  is a cutaway cross-sectional side view of an LCD pixel having liquid crystal molecules oriented to facilitate light passage, in accordance with aspects of the present disclosure; 
         FIG. 8  depicts liquid crystal molecules in a nematic phase, in accordance with aspects of the present disclosure; 
         FIG. 9  depicts a chiral dopant having twisted molecules, in accordance with aspects of the present disclosure; 
         FIG. 10  is a graph of driving voltage, response time and transmittance as a function of chiral dopant pitch ratio, in accordance with aspects of the present disclosure; 
         FIG. 11  is a cutaway cross-sectional side view of an LCD pixel having a polymer network disposed among the liquid crystal molecules, in accordance with aspects of the present disclosure; and 
         FIG. 12  is a flowchart of a method of manufacturing an LCD having a liquid crystal layer including a chiral dopant and a polymer network, 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 only exemplary 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 of the present disclosure, 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 reducing response time, decreasing driving voltage and/or increasing transmittance of an LCD panel. Certain embodiments may include a chiral dopant dispersed within a liquid crystal layer of the LCD. The chiral dopant may reduce response time and/or decrease driving voltage by biasing liquid crystal molecules toward a state that facilitates light passage through the LCD. The chiral dopant may also reduce response time and/or increase transmittance by biasing liquid crystal molecules toward a state that inhibits light passage through the LCD. Certain embodiments may include a polymer network disposed among the liquid crystal molecules and configured to reduce response time by biasing the molecules toward a state that inhibits light passage through the LCD. 
     With these foregoing features in mind, a general description of suitable electronic devices using LCD displays having such reduced response time, decreased driving voltage and/or increased 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 include 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 another 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 varying an electrical 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 electrical 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 electrical 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 referring once again to the figures,  FIG. 4  depicts an exploded view showing different layers that may be implemented in a unit pixel of an LCD  32 . The pixel, referred to herein by the reference number  60 , includes an upper polarizing layer  62  and a lower polarizing layer  64  that polarize light emitted by a light source  66 , which may be provided as a backlight assembly unit or a light-reflective surface. In embodiments where the light source  66  is a backlight assembly unit, any type of suitable lighting device, such as cold cathode fluorescent lamps (CCFLs), hot cathode fluorescent lamps (HCFLs), and/or light emitting diodes (LEDs), may be utilize to provide lighting. 
     As shown in the present embodiment, a lower substrate  68  is disposed above the lower polarizing layer  64 . The lower substrate  68  is generally formed from a light-transparent material, such as glass, quartz, and/or plastic. A thin film transistor (TFT) layer  70  is depicted as being disposed above the lower substrate  68 . For simplicity of illustration, the TFT layer  70  is depicted as a generalized structure in  FIG. 4 . In practice, the TFT layer  70  may itself include various conductive, non-conductive, and semiconductive layers and structures which generally form the electrical devices and pathways which drive operation of the unit pixel  60 . For example, in an embodiment in which the pixel  60  is part of an FFS LCD panel, the TFT layer  70  may include the respective data lines (also referred to as “source lines”), scanning lines (also referred to as “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  60 , be formed using transparent conductive materials, such as indium tin oxide (ITO) or indium zinc oxide (IZO), for example. The TFT layer  70  may further 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 electrodes and common electrodes, a TFT, and the respective data and scanning lines used to operate the unit pixel  60 , as described in further detail below with regard to  FIG. 5 . In the depicted embodiment, a lower alignment layer  71 , which may be formed from polyimide or other suitable materials, may be disposed between the TFT layer  70  and a liquid crystal layer  72 . 
     The liquid crystal layer  72  may include liquid crystal molecules suspended in a fluid or embedded in polymer networks. The liquid crystal molecules may be oriented or aligned with respect to an electrical field generated by the TFT layer  70 . In practice, the orientation of the liquid crystal molecules in the liquid crystal layer  72  determines the amount of light (e.g., provided by the light source  66 ) that is transmitted through the pixel  60 . Thus, by modulation of the electrical field applied to the liquid crystal layer  72 , the amount of light transmitted though the pixel  60  may be correspondingly modulated. 
     Disposed on the side of the liquid crystal layer  72  opposite from the TFT layer  70  may be one or more alignment and/or overcoating layers  74  interfacing between the liquid crystal layer  72  and an overlying color filter  76 . The color filter  76 , in certain embodiments, may be a red, green, or blue filter, such that each unit pixel  60  of the LCD  32  corresponds to a primary color when light is transmitted from the light source  66  through the liquid crystal layer  72  and the color filter  76 . 
     The color filter  76  may be surrounded by a light-opaque mask or matrix  78 , commonly referred to as a “black mask,” which circumscribes the light-transmissive portion of the unit pixel  60 . For example, in certain embodiments, the black mask  78  may be sized and shaped to define a light-transmissive aperture over the liquid crystal layer  72  and around the color filter  76  and to cover or mask portions of the unit 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 . Further, in addition to defining the light-transmissive aperture, the black mask  78  may serve to prevent light transmitted through the aperture and color filter  76  from diffusing or “bleeding” into adjacent unit pixels. 
     In the depicted embodiment, an upper substrate  80  may be further disposed between the color filter  76  (including the black mask  78 ) and the upper polarizing layer  62 . 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  70  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  72  ( FIG. 4 ) to modulate light transmission through the liquid crystal layer  72 . 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. 
     The operation of a pixel  60  of the LCD  32  and, particularly, the arrangement of the pixel electrodes  110  and the common electrodes discussed in  FIG. 5  may be better understood with respect to  FIG. 6 , which illustrates the operation of the pixel  60  via a cutaway cross-sectional side view. As shown, the view of the pixel  60  in  FIG. 6  includes the layers generally described above with reference to  FIG. 4 , including the upper polarizing layer  62 , lower polarizing layer  64 , lower substrate  68 , TFT layer  70 , liquid crystal layer  72 , alignment layers  71  and  74 , color filter  76 , and upper substrate  80 . 
     As mentioned above, the TFT layer  70 , which was depicted as a generalized structure in  FIG. 4 , may include various conductive, non-conductive, and/or semiconductive layers and structures defining electrical devices and pathways for driving the operation of pixels  60 . In the illustrated embodiment, the TFT layer  70  is shown in the context of a fringe field switching (FFS) LCD display device and includes the pixel electrode  110 , an insulating layer  132 , and a common electrode layer  134 . The common electrode layer  134  is disposed above the lower substrate  68 , and the insulating layer  132  is disposed between the pixel electrode  110  and the common electrode  134 . 
     The pixel electrodes  110  and the common electrode layer  134  may be made of a transparent conductive material, such as ITO or IZO, as mentioned above. The common electrode layer  134  generally spans the pixel  60 , and may be connected to a common line (not shown), which may be parallel to a scanning line  102 . The pixel electrodes  110  may be formed as having one or more slit-like voids  138 , such that the portions of the pixel electrode  110  define “strip-like” or “finger-like” electrode shapes that generally lie within a plane of the LCD  32  defined by the x-axis and y-axis (x-y plane), as depicted by the reference axes shown in  FIG. 6 . As shown in the present figure, portions of the lower alignment layer  71  may at least partially protrude into the region defined by the slits  138 . 
     In accordance with FFS LCD operating principles, liquid crystal molecules  136  within the liquid crystal layer  72  may have a “default” orientation in a first direction based upon the configuration (e.g., the “rub” direction) of the lower  71  and upper alignment layers  74 . For present explanatory purposes, the default orientation of the liquid crystal molecules  136  in the illustrated embodiment is generally along the y-axis of the LCD  32 . In other words, both the lower alignment layer  71  and the upper alignment layer  74  are configured to generally orient the liquid crystal molecules  136  along the y-axis. However, as will be appreciated, the default orientation of the liquid crystal molecules  136  may be generally along the x-axis, z-axis, or a combination of the three axes in further embodiments. Moreover, in certain embodiments, the default orientation may be angled with respect to one or more axes to facilitate rotation of the liquid crystal molecules in a uniform direction. 
     A thickness d of the liquid crystal layer  72  is defined by the spacing between the upper alignment layer  74  and the lower alignment layer  71 , also referred to as the cell gap. The thickness d of the liquid crystal layer  72  may affect various properties of the LCD  32  such as response time R, light transmittance T and/or driving voltage V, among other properties. For purposes of illustration, four liquid crystal molecules  136  are spaced between the alignment layers  71  and  74 . Certain embodiments may include more liquid crystal molecules  136  spaced along the z-axis. In addition, while the liquid crystal molecules  136  are depicted as being arranged in substantially parallel columns, embodiments may include liquid crystal molecules  136  offset in the x-axis. 
     In the default orientation, the liquid crystal molecules  136  are arranged to inhibit light passage through the LCD  32 . Specifically, in the present embodiment, the polarization axis of the lower polarizing layer  64  may be oriented approximately 90 degrees relative to the upper polarizing layer  62 . As will be appreciated, when light passes through a polarizing filter, the light becomes polarized along the polarization axis of the filter. In other words, the filter blocks the passage of light having any polarization axis other than the polarization axis of the filter. Therefore, light passing through the lower polarizing layer  64  may become polarized along the polarization axis of the lower polarizing layer  64 . If each liquid crystal molecule  136  is oriented along substantially the same axis as the lower polarizing layer  64 , the light may maintain its polarization axis while passing through the liquid crystal layer  72 . Therefore, when the light impacts the upper polarizing layer  62 , the polarization axis of the light is approximately 90 degrees offset from the polarization axis of the upper polarizing layer  62 . 
     As previously discussed, a polarizing filter blocks the passage of light having a polarization axis offset from the polarization axis of the filter. Therefore, because the light is polarized 90 degrees relative to the polarization axis of the upper polarizing layer  62 , substantially no light passes through the upper polarizing layer  62 . Consequently, the default orientation of the liquid crystal molecules  136  substantially inhibits the passage of light through the LCD  32 . 
     As illustrated in  FIG. 7 , liquid crystal molecules  136  may be oriented to facilitate light passage through the LCD  32 . Specifically, when a driving voltage V is applied to the pixel electrode  110 , an electrical field is formed between the pixel electrodes  110  and common electrode layer  134 . As discussed above, the electrical field (referred to herein by the reference label E) controls the orientation of liquid crystal molecules  136  within the liquid crystal layer  72 , such that the orientation changes with respect to the default orientation, thereby allowing at least a portion of the light transmitted from the light source  66  (not shown in  FIGS. 6 and 7 ) to be transmitted through the LCD  32 . Thus, by modulating the electrical field E, the light provided by the light source  66  and transmitted through the LCD  32  may be controlled. In this manner, image data sent along the data lines  100  and scanning lines  102  may be perceived by a user viewing the LCD  32  as an image. 
     For example, the liquid crystal molecules  136  in the present embodiment are configured to twist in response to the electrical field E. Specifically, the electrical field E may induce liquid crystal molecules  136  to rotate about the z-axis from an orientation substantially aligned with the y-axis toward an orientation substantially aligned with the x-axis. As will be appreciated, a magnitude of the electrical field E may decrease as distance from the pixel electrode  110  increases. As a result, the liquid crystal molecules  136  positioned closer to the pixel electrode  110  may rotate to a greater extent than the liquid crystal molecules  136  positioned farther from the pixel electrode  110 . Therefore, the liquid crystal molecules  136  may be arranged in a substantially twisted pattern, as illustrated in  FIG. 7 . 
     It is noted that the polarization axis of light may be influenced by the orientation of the liquid crystal molecules  136 . For example, light passing through the lower polarizing layer  64  may be polarized in a direction substantially parallel to the y-z plane. As the light passes through the twisted liquid crystal molecules  136 , the polarization axis of the light may rotate toward the x-z plane. Specifically, because molecule  136   a  is substantially oriented along the x-axis, molecule  136   a  may induce the polarization axis of the light to rotate toward the x-axis. Similarly, as the light passes through molecules  136   b  and  136   c , the polarization axis of the light may be further rotated because molecules  136   b  and  136   c  are at least partially oriented along the x-axis. Conversely, because molecule  136   d  is oriented substantially along the y-axis, the polarization axis of the light may rotate back toward the y-z plane. However, the overall orientation of the liquid crystal molecules  136  may establish a net rotation toward the x-z plane. Therefore, a portion of the light may pass through the upper polarizing layer  62  because the polarization axis of the light has rotated toward the polarization axis of the upper polarizing layer  62 , i.e., offset from the polarization axis of the lower polarizing layer  64  or rotated toward the x-z plane. 
     In this configuration, LCD  32  may facilitate light passage when electrical field E is activated and inhibit light passage when electrical field E is deactivated. As illustrated in  FIG. 7 , the light passes through the upper polarizing layer  62  in a direction L. As will be appreciated, alternative orientations of the polarizing layers  62  and  64 , as well as alternative configurations of the liquid crystal molecules  136  may be employed in further embodiments. Moreover, the electrical field E may cause the liquid crystal molecules  136  to rotate about other axes, such as the x-axis and/or the y-axis, in certain configurations. 
     The electrical field E may induce liquid crystal molecules  136  to rotate over a finite time period, T on . Rotation time T on  may be affected by a variety of factors such as viscosity of the liquid crystal layer  72 , spacing between pixel electrodes  110 , width of pixel electrodes  110 , thickness d of the liquid crystal layer  72  and/or magnitude of the electrical field E, among other factors. For example, rotation time T on  may be reduced by increasing the magnitude of the electrical field E. However, such an increased electrical field magnitude may involve applying additional driving voltage V between the pixel electrode  110  and the common electrode  134 . As a result, a battery within a portable device may be drained more rapidly. Therefore, it may be desirable to reduce rotation time T on  without increasing the electrical field magnitude. Similarly, it may be desirable to reduce the electrical field magnitude without increasing rotation time T on . 
     In addition, when the electrical field E is removed from the liquid crystal molecules  136 , the molecules  136  may rotate back to their initial state over a time period T off . The sum of the rotation time T on  and the realignment time T off  corresponds to the response time R of the LCD  32 . Alternative methods of computing response time R such as measuring a transition period between pixel states (e.g., gray-to-gray) may also be employed. Faster response time R may facilitate higher frame rates for video playback on the LCD  32  and/or smoother transitions between images. 
       FIG. 8  depicts a nematic phase liquid crystal material  140  that may be included within the liquid crystal layer  72 . As illustrated, the liquid crystal molecules  136  within the nematic phase material  140  may include directors n orientated in substantially the same direction. In other words, the liquid crystal molecules  136  may be substantially parallel to one another. Absent an external force, intermolecular forces between the liquid crystal molecules  136  of a nematic phase material  140  may maintain the molecules  136  in the illustrated orientation. Therefore, the nematic phase material  140  may be well suited for the previously described LCD  32  because the liquid crystal molecules  136  may remain oriented in one direction outside the presence of the electrical field E. Upon application of the electrical field E, liquid crystal molecules  136  within the nematic phase material  140  may twist as previously described. Conversely, once the electrical field E is deactivated, intermolecular forces may direct the liquid crystal molecules  136  to return to their original alignment, i.e., untwisted orientation. 
       FIG. 9  depicts a chiral dopant  142  that may be included within the liquid crystal layer  72 . As compared to the parallel molecules of the nematic phase material  140 , the chiral dopant  142  includes molecules  144  twisted about a longitudinal axis  146 . Specifically, directors n rotate about the longitudinal axis  146  in a counter-clockwise direction  148 , forming a right-handed or positive chiral dopant  142 . The twisted pattern is established by intermolecular forces that urge each molecule  144  to align at a slight angle to a neighboring molecule  144 . A pitch p of the chiral dopant  142  may be defined as the length over which the directors n rotate 360 degrees about the longitudinal axis  146 . The chiral dopant  142  illustrated in  FIG. 9  only shows an approximately 180 degree rotation of the directors n. Therefore, the length of the illustrated chiral dopant  142  is half of the pitch, p/2. The smaller the pitch, the greater the twist of the chiral dopant  142 . 
     In certain embodiments, the chiral dopant  142  may be dispersed within the nematic phase material  140  of the liquid crystal layer  72 . The naturally twisted orientation of the chiral dopant  142  may bias the nematic phase material  140  toward a twisted state. As previously discussed, the liquid crystal molecules  136  twist in response to an electrical field E, causing light to pass through the LCD  32 . For example, the liquid crystal molecules  136  in the embodiment depicted in  FIG. 7  are configured to twist in a counter-clockwise direction. Therefore, a right-handed chiral dopant  142  may bias the liquid crystal molecules  136  toward a twisted state that facilitates light transmission. By way of example, the right-handed chiral dopant  142  may be a dopant designated as CB15 available from Merck Chemicals of Darmstadt, Germany. Conversely, if the liquid crystal molecules  136  are configured to twist in a clockwise direction, a left-handed or negative chiral dopant  142  may bias the molecules  136  toward the twisted state. For example, the left-handed chiral dopant  142  may be a dopant designated as ZLI-811 available from Merck Chemicals. 
     The bias may reduce rotation time T on  by facilitating faster twisting of the liquid crystal molecules  136 . However, the bias may also increase realignment time T off  by the same mechanism. In certain configurations, the reduction in T on  may be greater than the increase in T off , thus establishing a net faster response time R of the LCD  32 . Furthermore, the magnitude of the electrical field E may be reduced due to the biasing effect of the chiral dopant  142 . For example, the chiral dopant  142  may enable a smaller electrical field to produce a similar response time R to a larger electrical field without the presence of the chiral dopant  142 . This configuration may reduce the driving voltage V, thereby decreasing electrical power consumption of the LCD  32  and enhancing battery life for portable devices. 
     The concentration and the pitch p of the chiral dopant  142  may influence the degree of bias on the liquid crystal molecules  136 , and hence the reduction in response time R and/or electrical field E magnitude. For example, the smaller the pitch p, the greater the biasing effect on the nematic phase material  140 . Pitch p may be expressed as a non-dimensional ratio d/p between the thickness d of the liquid crystal layer  72  and the pitch p of the chiral dopant  142 . Certain embodiments may employ a chiral dopant  142  with a pitch ratio d/p of less than about 1. Further embodiments may employ chiral dopants  142  having a pitch ratio d/p of approximately 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.7, 0.8, 0.9 or any pitch ratio d/p therebetween. Increased pitch ratios d/p, having smaller pitches p, may produce faster response times R and/or reduced electrical consumption. 
     Similarly, the biasing effect on the nematic phase material  140  may be proportional to the concentration of the chiral dopant  142 . In other words, higher chiral dopant concentrations may increase the twisting bias on the nematic phase material  140 . Certain embodiments may include a liquid crystal layer  72  having less than 1% chiral dopant  142  by weight. Other embodiments may employ chiral dopant weight concentrations of approximately 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.5%, 0.75%, 0.9%, or any concentration therebetween. Higher chiral dopant concentrations may reduce response time R and/or driving voltage V. 
     However, excessive chiral dopant concentrations may cause the liquid crystal molecules  136  to twist outside the presence of the electrical field E. Such a condition may be undesirable because the electrical field E may no longer be capable of sufficiently modulating light passage through each pixel  60  of the LCD  32 . In other words, each pixel  60  may allow light to pass through without the influence of the electrical field E. As a result, images may not be properly formed on the LCD  32 . Therefore, in one embodiment, the concentration of chiral dopant  142  may be particularly selected to bias the liquid crystal molecules  136  toward a twisted state without causing the molecules  136  to twist. 
     Furthermore, the chiral dopant  142  may reduce the transmittance T of light through the LCD  32 .  FIG. 10  is a graph  150  of the effect of pitch ratio d/p on the response time R, driving voltage V and transmittance T. Specifically, the x-axis represents the pitch ratio d/p and the y-axis generally represents the driving voltage V, the response time R and the transmittance T. Curve  152  illustrates the relationship between pitch ratio d/p and driving voltage V. As previously discussed, as pitch ratio d/p increases, driving voltage V may be decreased. Similarly, as illustrated by curve  154 , as pitch ratio d/p increases, response time R may decrease. Furthermore, as represented by curve  156 , transmittance T may also decrease as pitch ratio d/p increases. While the above relationships are depicted as linear for purposes of illustration, the shape of curves  152 ,  154  and  156  may be dependent on the LCD  32  configuration. For example, concentration of chiral dopant  142  within the liquid crystal layer  72  may affect the shape of curves  152 ,  154  and  156 . 
     For example, the following table presents simulation data of the effect of pitch ratio d/p on rotation time T on , realignment time T off , response time R, driving voltage V and transmittance T. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 d/p 
                 T on  (ms) 
                 T off  (ms) 
                 R (ms) 
                 V (v) 
                 T (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 0 
                 16.4 
                 22.2 
                 38.6 
                 5.0 
                 17.90 
               
               
                   
                 0.2 
                 14.0 
                 22.8 
                 36.8 
               
               
                   
                 0.5 
                 9.9 
                 24.2 
                 34.1 
                 4.3 
                 16.48 
               
               
                   
                 0.8 
                   
                   
                   
                 3.2 
                 13.42 
               
               
                   
                   
               
            
           
         
       
     
     In alternative embodiments, a chiral dopant  142  may be included within liquid crystal layer  72  that biases the liquid crystal molecules  136  toward an untwisted or aligned state. For example, the liquid crystal molecules  136  in the embodiment depicted in  FIG. 7  are configured to twist in a counter-clockwise direction. Therefore, a left-handed chiral dopant  142  may bias the liquid crystal molecules  136  toward an untwisted state that substantially inhibits light transmission. Conversely, if the liquid crystal molecules  136  are configured to twist in a clockwise direction, a right-handed chiral dopant  142  may bias the molecules  136  toward an untwisted state. 
     This reverse bias may reduce realignment time T off  by facilitating faster realignment of the liquid crystal molecules  136 . However, the reverse bias may also increase rotation time T on  by the same mechanism. In certain configurations, the reduction in T off  may be greater than the increase in T on , thus establishing a net faster response time R of the LCD  32 . However, the magnitude of the electrical field E may be increased due to the reverse biasing effect of the chiral dopant  142 . In other words, additional driving voltage V may be applied to achieve a desired response time R. Another effect of the reverse bias may be an increase in transmittance T due to better alignment of liquid crystal molecules  136  within the LCD  32 . Therefore, selection of right-handed or left-handed chiral dopant may be dependent on desired performance characteristics of the LCD  32 . 
     For example, the following table presents simulation data of the effect of pitch ratio d/p on rotation time T on , realignment time T off , response time R, driving voltage V and transmittance T for a reverse biasing chiral dopant. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 d/p 
                 T on  (ms) 
                 T off  (ms) 
                 R (ms) 
                 V (v) 
                 T (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 0 
                 16.4 
                 22.2 
                 38.6 
                 5.0 
                 17.90 
               
               
                   
                 0.2 
                 18.6 
                 21.8 
                 40.4 
                 5.1 
                 18.00 
               
               
                   
                 0.5 
                 19.0 
                 20.6 
                 39.6 
                 5.2 
                 18.13 
               
               
                   
                   
               
            
           
         
       
     
     In certain embodiments, a polymer network may be disposed among the liquid crystal molecules  136  of the liquid crystal layer  72 .  FIG. 11 , a cross-sectional view of a pixel  60  of the LCD  32 , presents a representation of a polymer network  158 . The polymer network  158  may include a complex of polymer strands disposed among the liquid crystal molecules  136 . In certain configurations, the polymer network  158  may reduce response time R by biasing the liquid crystal molecules  136  toward an untwisted state. The concentration of the polymer network  158  may be less than about 25% of the liquid crystal layer  72  by weight. Further embodiments may employ a polymer network concentration of less than about 10% of the liquid crystal layer  72  by weight. Other embodiments may have polymer network concentrations less than approximately 1%, 2%, 4%, 6%, 8%, 12%, 15%, or 20%. 
     In certain embodiments, polymer strands may limit the rotation of the liquid crystal molecules  136 . For example, when an electrical field E is applied, the liquid crystal molecules  136  may rotate. However, due to the presence of the polymer network  158 , the liquid crystal molecules  136  may experience resistance to rotation. Specifically, certain liquid crystal molecules  136  may contact the polymer strands as the molecules  136  rotate, causing the strands to stretch. Due to the plastic nature of the polymer strands, the deformed polymer network  158  may bias the liquid crystal molecules  136  toward the untwisted state, thereby reducing the realignment time T off . Furthermore, the biasing effect may also increase T on  and/or the magnitude of the electrical field E needed to maintain T on  because the molecules  136  may experience resistance to rotation. However, the increase in rotation time T on  may be less than the decrease in realignment time T off , resulting in a net reduction in response time R. 
     Additionally, in at least some embodiments, the polymer network  158  may improve the tolerance of the LCD  32  to mechanical distortion. For example, as generally noted above, an LCD panel including pixels  60  may be configured such that, in the absence of an electric field, the liquid crystal molecules  136  are substantially oriented parallel to the polarization axis of the lower polarizing layer  64  and perpendicular to the polarization axis of the upper polarizing layer  62 . While this configuration generally inhibits light transmission through the upper polarizing layer  62 , various mechanical forces acting on the LCD panel, such as pressure on certain portions of the panel from mounting components, user interaction with the panel, or the like, may be transmitted to some of the liquid crystal molecules  136 . Such mechanical forces on some of the liquid crystal molecules  136 , in turn, may cause these molecules to rotate into a different orientation, thus impacting the amount of light allowed to pass through the affected portions of the LCD panel. In some embodiments, however, the inclusion of the polymer network  158  may stabilize the liquid crystal layer  72  and reduce the magnitude of rotation of liquid crystal molecules  136  in response to mechanical forces on the LCD panel. 
     Certain embodiments may include both a polymer network  158  and a chiral dopant  142  within the liquid crystal layer  72 . Parameters of the polymer network  158  and the chiral dopant  142  may be configured to further reduce response time R, decrease driving voltage V and/or increase transmittance T. For example, a right-handed chiral dopant  142  may be dispersed within a liquid crystal layer  72  having molecules  136  configured to twist in a counter-clockwise direction. As previously discussed, this configuration may reduce rotation time T on , but increase realignment time T off . In addition, a polymer network  158  may be disposed among the molecules  136  of the liquid crystal layer  72 . The polymer network may reduce realignment time T off , but increase rotation time T on . By adjusting parameters of the chiral dopant  142  (e.g., pitch ratio d/p and/or concentration) and the polymer network  158  (e.g., concentration), a reduction in both rotation time T on  and realignment time T off  may be achieved. Therefore, response time R may be reduced in such configurations, thereby facilitating higher frame rates and/or smoother transitions between images on the LCD  32 . 
       FIG. 12  is a flowchart of a method  160  of manufacturing an LCD  32  having a liquid crystal layer  72  including a chiral dopant  142  and a polymer network  158 . As represented by block  162 , the method  160  begins by disposing nematic liquid crystal material  140  between the alignment layers  71  and  74 . As previously discussed, the alignment layers  71  and  74  may serve to align the liquid crystal molecules  136  in an untwisted state. Chiral dopant  142  may then be dispersed within the nematic liquid crystal material  140 , as represented by block  164 . The chiral dopant  142  may be configured to decrease response time R, reduce driving voltage V and/or increase transmittance T. Finally, as represented by block  166 , a polymer network  158  may be disposed between the alignment layers  71  and  74  with the liquid crystal layer  72 . For example, the nematic material  140  and the chiral dopant  142  may be mixed with a solution capable of polymerization (pre-polymer). The solution may then be polymerized, forming a polymer network  158  within the liquid crystal layer  72 . As will be appreciated, other methods of forming a polymer network  158  may be employed in alternative embodiments. 
     The order of steps within method  160  may be rearranged in alternative embodiments. For example, the chiral dopant  142  may be dispersed within the nematic liquid crystal material  140  prior to disposing the mixture between the alignment layers  71  and  74 . Similarly, the pre-polymer solution may be mixed with the nematic material  140  and/or the chiral dopant  142  prior to disposition between the alignment layers  71  and  74 . Furthermore, the nematic liquid crystal material  140 , the chiral dopant  142  and/or the pre-polymer solution may be disposed on the lower alignment layer  71 . The upper alignment layer  74  may then be placed over the mixture, forming the liquid crystal layer  72 . 
     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: 20090331
Publication Date: 20121023
Grant Date: 20121023
Priority Date: 20090331
Inventors: CHEN CHENG
ZHONG JOHN Z.
XU MING
GU MINGXIA
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/1396", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": true, "first": false, "tree": "[]"}, {"code": "C09K19/586", "inventive": true, "first": true, "tree": "[]"}, {"code": "C09K19/586", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1396", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13775", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13775", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 42783763