PATENT DOCUMENT

Publication Number: US-9305941-B2
Application Number: US-201213667942-A
Country: US
Kind Code: B2

Title: Device and method for improving AMOLED driving

Abstract:
Devices and methods for increasing the aperture ratio and providing more precise gray level control to pixels in an active matrix organic light emitting diode (AMOLED) display are provided. By way of example, one embodiment includes disposing a gate insulator and an interlayer dielectric material between a gate electrode of a thin-film transistor of a driving circuit and a channel of the thin-film transistor. The improved structure of the driving circuit facilitates a higher voltage range for controlling the gray level of the pixels, and may increase the aperture ratio of the pixels.

Claims:
What is claimed is: 
     
       1. A display for an electronic device comprising: an array of pixels, each pixel comprising:
 a portion of a first thin-film transistor (TFT) disposed over a substrate, wherein the portion of the first TFT comprises a first source, a first drain, and a first channel disposed adjacent to the first source and the first drain; 
 a portion of a second TFT disposed over the substrate, wherein the portion of the second TFT comprises a second source, a second drain, and a second channel disposed adjacent to the second source and the second drain; 
 a first via directly and electrically coupled to the first drain of the first TFT; 
 a first insulator layer disposed over the portion of the first TFT and the portion of the second TFT; 
 a first gate of the first TFT disposed over the first insulator layer; 
 a second insulator layer disposed over the first insulator layer and the first gate of the first TFT; 
 a contact disposed over the second insulator layer and directly and electrically coupled to the via; 
 and a second gate of a second TFT disposed over the second insulator layer and directly and electrically coupled to the contact; 
 wherein the deposition of the second gate of the TFT over the second insulator layer reduces a capacitance between the second gate and the second channel; 
 wherein an accuracy of a gray level control of the pixel is increased due to the reduced capacitance; and 
 wherein the deposition of the contact and the second gate of the TFT over the second insulator layer reduces a width of the electrical coupling between the contact and the second gate, thereby allowing an increased pixel aperture ratio. 
 
     
     
       2. The display of  claim 1 , comprising a third insulator layer disposed over the second gate of the second TFT. 
     
     
       3. The display of  claim 1 , comprising a second via directly coupled to the second source and extending through the first insulator layer and the second insulator layer. 
     
     
       4. The display of  claim 1 , comprising a pixel electrode disposed over the second insulator layer. 
     
     
       5. The display of  claim 1 , comprising a conductor configured to electrically couple the second drain to a pixel electrode. 
     
     
       6. The display of  claim 1 , comprising an organic light emitting diode (OLED) layer disposed over the second insulator layer. 
     
     
       7. The display of  claim 1 , comprising a top electrode layer disposed over the second insulator layer. 
     
     
       8. An electronic display comprising:
 a matrix of pixels, each pixel comprising:
 a portion of a driving thin-film transistor (TFT) comprising a first source, a first drain, and a first channel; 
 a portion of a circuit TFT comprising a second source, a second drain, and a second channel; 
 a via directly and electrically coupled to the second drain; 
 a gate insulator layer disposed over the portion of the driving TFT and the portion of the circuit TFT; 
 a dummy gate electrode of the driving TFT and a first gate of the circuit TFT disposed over the gate insulator layer; 
 an interlayer dielectric (ILD) disposed over the dummy gate electrode and the first gate of the circuit TFT; 
 a contact disposed directly over the ILD and directly and electrically coupled to the via; 
 a gate of the driving TFT disposed over the ILD; and 
 a connection formed between the gate of the driving TFT and the contact and disposed over the ILD, wherein the deposition of the connection over the ILD reduces a width of the connection, thereby allowing an increased pixel aperture ratio of the pixel; 
 wherein the gate of the driving TFT is directly and electrically coupled to the second drain of the circuit TFT and the contact; 
 whereby the circuit TFT is configured to control an activation and a deactivation of the driving TFT; and 
 wherein a first height between the gate of the driving TFT and the first channel is larger than a second height between the gate of the circuit switching TFT and the second channel. 
 
 
     
     
       9. The electronic display of  claim 8 , comprising an insulator layer disposed over the gate of the driving TFT and the ILD. 
     
     
       10. The electronic display of  claim 8 , comprising a pixel electrode disposed over the ILD and electrically coupled to the first drain. 
     
     
       11. The electronic display of  claim 8 , comprising an organic light emitting diode (OLED) layer disposed over the ILD. 
     
     
       12. The electronic display of  claim 8 , comprising a top electrode layer disposed over the ILD. 
     
     
       13. The electronic display of  claim 8 , wherein the electronic display is an active matrix organic light emitting diode display. 
     
     
       14. A display comprising:
 an array of pixels, each pixel comprising:
 a portion of a first driving TFT and a portion of a circuit TFT comprising a drain disposed over a substrate; 
 a via directly and electrically coupled to the drain of the circuit TFT; 
 a gate insulator layer disposed over the portion of the first driving TFT and the portion of the circuit TFT; 
 a gate of the circuit TFT disposed over the gate insulator layer; 
 an inter-layer dielectric (ILD) disposed over the gate insulator layer and the gate of the circuit TFT; 
 a contact directly disposed over the ILD and directly and electrically coupled to the via; and 
 a gate of the first driving TFT disposed over the ILD and directly and electrically coupled to the drain of the circuit TFT by the contact and the via; 
 wherein the deposition of the gate of the first driving TFT over the ILD reduces a capacitance between the gate of the first driving TFT and the portion of the first driving TFT; 
 wherein an accuracy of a gray level control of the pixel is increased due to the reduced capacitance; and 
 wherein the deposition of the contact and the gate of the first driving TFT over the ILD reduces a width of the electrical coupling between the contact and the gate of the first driving TFT, thereby allowing an increased pixel aperture ratio. 
 
 
     
     
       15. The display of  claim 14 , comprising an insulator layer disposed over the ILD and the gate of the driving TFT. 
     
     
       16. The display of  claim 14 , comprising a pixel electrode disposed over the ILD and is electrically coupled to a drain of the driving TFT. 
     
     
       17. The display of  claim 14 , comprising an organic light emitting diode (OLED) layer disposed over the ILD. 
     
     
       18. The display of  claim 14 , comprising a top electrode layer disposed over the ILD. 
     
     
       19. A method comprising:
 disposing a portion of a first driving TFT and a portion of a circuit TFT comprising a drain over a substrate; 
 disposing a gate insulator layer over the portion of the first driving TFT and the portion of the circuit TFT; 
 disposing a gate of the circuit TFT over the gate insulator layer; 
 disposing a via over the portion of the circuit TFT; 
 directly and electrically coupling the via to the drain of the circuit TFT; 
 disposing an interlayer dielectric (ILD) over the gate insulator layer and the gate of the circuit TFT, wherein the via is configured to extend through the ILD; 
 disposing a contact directly over the ILD; 
 directly and electrically coupling the contact to the via; 
 disposing a gate of the first driving TFT over a portion of the ILD; 
 directly and electrically coupling the gate of the first driving TFT to the contact; and 
 electrically coupling an organic light emitting diode (OLED) layer to the first driving TFT; 
 wherein the deposition of the gate of the first driving TFT over the portion of the ILD increases an accuracy of a gray level control of a pixel comprising the first driving TFT, the circuit TFT, the gate insulator layer, the ILD, and the OLED layer; and 
 wherein the deposition of the contact and the gate of the first driving TFT over the ILD reduces the width of the electrical coupling between the contact and the gate of the first driving TFT, thereby allowing an increased pixel aperture ratio of the pixel. 
 
     
     
       20. The method of  claim 19 , comprising disposing a pixel electrode over the ILD layer, wherein the pixel electrode is electrically coupled to a drain of the driving TFT and to the OLED layer. 
     
     
       21. The method of  claim 20 , comprising disposing an insulator layer over the ILD, the gate of the driving TFT, and the pixel electrode. 
     
     
       22. The method of  claim 21 , comprising disposing a top electrode layer extending over the OLED layer and the insulator layer. 
     
     
       23. An apparatus, comprising:
 a display panel, wherein the display panel comprises a plurality of unit pixel comprising:
 a portion of a first thin-film transistor (TFT) disposed over a substrate, wherein the portion of the TFT comprises a first source, a first drain, and a first channel disposed adjacent to the first source and the first drain; 
 a portion of a second TFT disposed over the substrate, wherein the portion of the second TFT comprises a second source, a second drain, and a second channel disposed adjacent to the second source and the second drain; 
 a first insulator layer disposed over the portion of the first TFT and the portion of the second TFT; 
 a gate of the second TFT disposed over the first insulator layer; 
 a second insulator layer disposed over the first insulator layer and the gate of the second TFT; 
 a via directly and electrically coupled to the second drain of the second TFT, wherein the via is configured to extend through the first and second insulator layers; 
 a contact disposed over the second insulator layer and directly and electrically coupled to the via; and 
 a gate of the first TFT disposed over the second insulator layer and directly and electrically coupled to the contact disposed over the second insulator layer and the via, thereby reducing a width of the connection and allowing an increased a pixel aperture ratio of the pixel; 
 
 a processing device coupled to the display panel; and 
 a housing comprising the display panel and the processing device. 
 
     
     
       24. The apparatus of  claim 23 , comprising a top electrode layer disposed over the second insulator layer.

Description:
BACKGROUND 
     The present disclosure relates generally to electronic displays and, more particularly, to devices and methods for achieving more precise gray level control and an increased aperture ratio in active matrix organic light emitting diode (AMOLED) electronic displays. 
     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. 
     Flat panel displays, such as AMOLED displays, are commonly used in 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 display panels typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, such devices may 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. 
     AMOLED displays typically include picture elements (e.g. pixels) arranged in a matrix to display an image that may be viewed by a user. Individual pixels of an AMOLED display may generate light as a voltage is applied to each pixel. The voltage applied to a pixel of an AMOLED display may be regulated by two thin film transistors (TFTs). For example, a circuit switching TFT may be used to regulate current flowing into a storage capacitor, and a driving TFT may be used to regulate the voltage being provided to the OLED of an individual pixel. Connections between the TFTs in an AMOLED display may extend through an area of the pixel that may otherwise be used for displaying image data. In certain configurations, a pixel aperture ratio is a ratio between a transparent area of the pixel that can be used to display image data and a total area of the pixel. Thus, connections between the TFTs may decrease the area of a pixel that can be used to display image data and thereby lower the aperture ratio of pixels of the AMOLED display. 
     In electronic displays, the gray level of each pixel may determine the intensity of the output of the pixel. In certain displays, the intensity of each pixel&#39;s output may vary from black at the lowest intensity to white at the highest intensity. As mentioned above, one of the TFTs of an AMOLED display may regulate a voltage being provided to the OLED of an individual pixel. The range of voltages that is applied to a gate electrode of the driving TFT may determine the amount of current flowing to the OLED and thus, the gray scale level of a pixel. An increased range of voltages that may be applied to the gate of the driving TFT may give more precise control over the gray level in an AMOLED display. 
     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. 
     Embodiments of the present disclosure relate to devices and methods for increasing the aperture ratio and the gray level control of pixels of an AMOLED display. For example, a display for an electronic device may include a driving thin film transistor (TFT) having a first source, a first drain, a first channel, and a first gate electrode. Additionally, a circuit switching TFT may include a second source, a second drain, a second channel, and a second gate electrode. A gate insulator layer may be disposed over the first source, the first drain, and the first channel of the driving TFT, and the second source, the second drain, and the second channel of the circuit switching TFT. The second gate electrode of the circuit switching TFT may be disposed over the gate insulating layer. An interlayer dielectric (ILD) may be disposed over the gate insulating layer and the second gate electrode of the circuit switching TFT. The first gate electrode of the driving TFT may be disposed over the ILD. Disposing the first gate electrode over the ILD may allow a direct electrical connection to the second source of the circuit switching TFT. This direct connection may decrease an area occupied by the connection circuitry mentioned above. Moreover, because the area of the direct connection is reduced, the pixel aperture ratio of pixels of the display may be increased. Additionally, disposing the gate electrode over the ILD rather than over the gate insulator layer produces a larger separation between the gate electrode and the channel of the driving TFT. The larger separation may increase the voltage range applied to the gate electrode and improve the gray level control. 
     Various refinements of the features noted above may be made in relation to various aspects of the present disclosure. 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 disclosure alone or in any combination. 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 
       Various aspects of this disclosure may be better understood 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 which may include a driving thin film transistor (TFT), in accordance with an embodiment of the disclosure; 
         FIG. 2  is a front view of a handheld electronic device, in accordance with an embodiment of the disclosure; 
         FIG. 3  is a perspective view of a notebook computer, in accordance with an embodiment of the disclosure; 
         FIG. 4  is a circuit diagram illustrating a portion of a matrix of unit pixels of the display device of  FIG. 1 , in accordance with an embodiment of the disclosure; 
         FIG. 5  is a graph depicting a relationship between a gate voltage and a drain current for the TFT of an active matrix organic light emitting diode (AMOLED) display, in accordance with an embodiment of the disclosure; 
         FIG. 6  is a cross-sectional view of a portion of an AMOLED display having a driving TFT, in accordance with an embodiment of the disclosure; 
         FIG. 7  is a flowchart of a process for manufacturing an AMOLED unit pixel for use in a display, in accordance with an embodiment of the disclosure; 
         FIG. 8  is a top view of the portion of the AMOLED display having the driving TFT of  FIG. 7 , in accordance with an embodiment of the disclosure; 
         FIG. 9  is a cross-sectional view of a portion of an AMOLED display having a driving TFT with a floating gate, in accordance with an embodiment of the disclosure; and 
         FIG. 10  is a flowchart of a process for manufacturing an AMOLED display. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are 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,” 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. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     As mentioned above, present embodiments relate to electronic displays, particularly to active matrix organic light emitting diode (AMOLED) displays. In particular, present embodiments include devices to increase the aperture ratio of pixels and the gray level control of pixels of an AMOLED display. Additionally, present embodiments include methods for fabricating AMOLED displays that have increased pixel aperture ratios. The pixel aperture ratios may be increased by reducing the area of connection circuitry within pixels of a display. Moreover, present embodiments include methods for fabricating AMOLED displays that have increased gray level control of pixels. The gray level control of pixels may be increased by increasing the distance between a gate electrode and a channel of a driving TFT. 
     With the foregoing in mind, a general description of suitable electronic devices that may employ electronic displays having pixels with improved gray level control and a larger pixel aperture ratio is described below. In particular,  FIG. 1  is a block diagram depicting various components that may be present in an electronic device suitable for use with such a display.  FIGS. 2 and 3  respectively illustrate perspective and front views of a suitable electronic device, which may be, as illustrated, a notebook computer or a handheld electronic device. 
       FIG. 1  is a block diagram illustrating the components that may be present in such an electronic device  8  and which may allow the device  8  to function in accordance with the techniques discussed herein. Those of ordinary skill in the art will appreciate that the various functional blocks shown in  FIG. 1  may comprise hardware elements (including circuitry), software elements (including computer code stored on a computer-readable medium) or a combination of both hardware and software elements. It should further be noted that  FIG. 1  is merely one example of a particular implementation and is merely intended to illustrate the types of components that may be present in a device  8 . For example, in the presently illustrated embodiment, these components may include a display  10 , I/O ports  12 , input structures  14 , one or more processors  16 , a memory device  18 , a non-volatile storage  20 , expansion card(s)  22 , a networking device  24 , and a power source  26 . As will be appreciated, the overall quality of image data shown on the display  10  may be affected by the controllability of gray levels and aperture ratios of the pixels of the display  10 . 
     With regard to each of these components, the display  10  may be used to display various images generated by the device  8 . Specifically, in certain embodiments, the display  10  may be an AMOLED display. 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 touch screen, 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 (e.g., 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 suitable 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 as 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  (e.g., 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 power 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 (e.g., 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 LANs or WANs. 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®, iPhone®, or iPad® available from Apple Inc. of Cupertino, Calif. 
     In the depicted embodiment, the handheld device  30  includes an enclosure or body  31  that protects the interior components from physical damage and shields them from electromagnetic interference. The enclosure  31  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  31  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 AMOLED display  32 . The AMOLED display  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 display  10 . Generally, the GUI  34  may include graphical elements that represent applications and functions of the handheld device  30 . 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 handheld device  30  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 touch screen included in the display  10 , or may be selected by a user input structure  14 , such as a wheel or button. 
     The handheld electronic device  30  also may include various input and output (I/O) ports  12  that allow connection of the handheld device  30  to external devices. For example, one I/O port  12  may be a port that allows the transmission and reception of data or commands between the handheld electronic device  30  and another electronic device, such as a computer. Such an I/O port  12  may be a proprietary port from Apple Inc. or may be an open standard I/O port. 
     In addition to handheld devices  30 , such as the depicted cellular telephone of  FIG. 2 , an electronic device  8  may also take the form of a computer or other type of electronic device. Such computers may include computers that are generally portable (such as laptop, notebook, and tablet computers) as well as computers that are generally used in one place (such as conventional desktop computers, workstations and/or servers). In certain embodiments, the electronic device  8  in the form of a computer may be a model of a MacBook®, MacBook® Pro, MacBook Air®, iMac®, Mac® mini, Mac Pro®, or iPad® 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. The depicted computer  50  includes a housing  52 , a display  10  (e.g., the AMOLED display  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 display  10 . 
     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. 
     It should be noted that the electronic device  8  having the presently disclosed display  10  may include devices other than those discussed as examples. Further, the electronic device may also include any device having a display  10  such as a television, a stand-alone display device, and so forth. 
     As mentioned, the display  10  of the electronic device may be an AMOLED display  32 . The AMOLED display  32  includes a matrix of pixels that contain light emitting circuitry. Accordingly,  FIG. 4  illustrates circuitry including a portion of a matrix of pixels of the display  10 . As illustrated, the display  10  may include a display panel  60 . Moreover, the display panel  60  may include multiple unit pixels  62  arranged as an array or matrix defining multiple rows and columns of unit pixels  62  that collectively form a viewable region of the display  10  in which an image may be displayed. In such an array, each unit pixel  62  may be defined by the intersection of rows and columns, represented here by the illustrated gate lines  64  (also referred to as “scanning lines”) and source lines  66  (also referred to as “data lines”), respectively. Additionally, power supply lines  68  may provide power to each of the unit pixels  62 . 
     Although only six unit pixels, referred to individually by reference numbers  62   a - 62   f , respectively, are shown, it should be understood that in an actual implementation, each source line  66  and gate line  64  may include hundreds or even thousands of such unit pixels  62 . By way of example, in a color display panel  60  having a display resolution of 1024×768, each source line  66 , which may define a column of the pixel array, may include 768 unit pixels, while each gate line  64 , which may define a row of the pixel array, may include 1024 groups of unit pixels with each group including a red, blue, and green pixel, thus totaling 3072 unit pixels per gate line  64 . By way of further example, the panel  60  may have a resolution of 480×320 or 960×640. In the presently illustrated example, the unit pixels  62   a - 62   c  may represent a group of pixels having a red pixel ( 62   a ), a blue pixel ( 62   b ), and a green pixel ( 62   c ). The group of unit pixels  62   d - 62   f  may be arranged in a similar manner. Additionally, in the industry, it is also common for the term “pixel” may refer to a group of adjacent different-colored pixels (e.g., a red pixel, blue pixel, and green pixel), with each of the individual colored pixels in the group being referred to as a “sub-pixel.” 
     Each unit pixel  62   a - 62   f  shown in  FIG. 4  includes two thin-film transistors (TFTs)  70 , a driving TFT  72  and a circuit switching TFT  74 . The driving TFT  72  may include a source  76 , a drain  78 , and a gate  80 . Likewise, the circuit switching TFT  74  may include a source  82 , a drain  84 , and a gate  86 . In the illustrated embodiment, the source  76  of each driving TFT  72  may be electrically coupled to a power supply line  68 . Similarly, the drain  78  of each driving TFT  72  may be electrically connected to an organic light emitting diode (OLED)  88 . Furthermore, the source  82  of each circuit switching TFT  74  may be electrically connected to a source line  66 , while the drain  84  of each circuit switching TFT  74  may be electrically connected to the gate  80  of each driving TFT  72 . A gate  86  of each circuit switching TFT  74  may be electrically connected to a gate line  64 . Each TFT  70  serves as a switching element and may be activated and deactivated (e.g., switched on and off) for a predetermined period based upon the respective presence or absence of a gate activation signal (also referred to as a scanning signal) at the gates of the TFTs  70 . Furthermore, a storage capacitor  89  may be electrically connected to a drain  84  of each circuit switching TFT  74  and a gate line  64  of a different unit pixel  62 . 
     The display  10  also includes a source driver integrated circuit (IC)  90 , which may include a chip, such as a processor or ASIC, configured to control various aspects of the display  10  and panel  60 . For example, the source driver IC  90  may receive image data  92  from the processor(s)  16  and send corresponding image signals to the unit pixels  62  of the panel  60 . The source driver IC  90  may also be coupled to a gate driver IC  94 , which may be configured to provide/remove gate activation signals to activate/deactivate rows of unit pixels  62  via the gate lines  64 . The source driver IC  90  may include a timing controller that determines and sends timing information  96  to the gate driver IC  94  to facilitate activation and deactivation of individual rows of unit pixels  62 . In other embodiments, timing information may be provided to the gate driver IC  94  in some other manner (e.g., using a timing controller that is separate from the source driver IC  90 ). Further, while  FIG. 4  depicts only a single source driver IC  90 , it should be appreciated that other embodiments may utilize multiple source driver ICs  90  to provide image signals  96  to the unit pixels  62 . For example, additional embodiments may include multiple source driver ICs  90  disposed along one or more edges of the panel  60 , with each source driver IC  90  being configured to control a subset of the source lines  66  and/or gate lines  64 . 
     In operation, the source driver IC  90  receives image data  92  from the processor  16  or a discrete display controller and, based on the received data, outputs signals to control the unit pixels  62 . For instance, to display image data  92 , the source driver IC  90  and the gate driver IC  94  may respectively supply voltage to the source  82  and gate  86  of the circuit switching TFT  74  to charge each storage capacitor  89 . The storage capacitor  89  may drive the gate  80  of the driving TFT  72  to provide a current from the power supply  98  to the OLED  88  of each unit pixel  62 . As may be appreciated, the color of a particular unit pixel depends on the color of the corresponding OLED  88 . The above-described process may be repeated for each row of pixels  62  in the panel  60  to reproduce image data  92  as a viewable image on the display  10 . 
     As mentioned above, pixels of the display  10  contain TFTs to drive and control the current being supplied to the display circuitry.  FIG. 5  is a graph  110  depicting a curve  112  for driving a TFT in a display  10 . The x-axis of the graph  110  represents a gate voltage  114  of the driving TFT  72 . The y-axis of the graph  110  represents a drain current  116  of the driving TFT  74 . A box  118  on the graph  110  shows the TFT gate voltage operation range. A larger gate voltage operation range may facilitate improved control of the gray level of each pixel in the display  10 . Additionally, a larger gate voltage operation range for a given current range may decrease the slope of the curve  112 . When the slope of the curve  112  decreases, a same gate voltage variation  120  may cause a smaller drain current difference  122 , thereby facilitating improved control of the gray level of each pixel in a display  10 . 
     The display  10  may be manufactured to facilitate greater control of gray levels of pixels and to increase the aperture ratio of pixels. Accordingly,  FIG. 6  illustrates a cross-sectional view of a unit pixel  62  of such a display  10 . The cross-sectional view of  FIG. 6  will be discussed in conjunction with  FIG. 7 .  FIG. 7  illustrates a flowchart  160  of a process for manufacturing the unit pixel  62  of  FIG. 6 . The unit pixel  62  may be formed from several layers. Specifically, the unit pixel  62  may include a substrate  130 , and one or more thin-film transistor (TFT) layers disposed on the substrate  130 , as represented by block  162  of  FIG. 7 . In the embodiment illustrated in  FIG. 6 , the unit pixel  62  includes the driving TFT  72  and the circuit switching TFT  74 . The driving TFT  72  includes the source  76 , a channel  132 , the drain  78 , and the gate  80 . Moreover, the circuit switching TFT  74  includes the source  82 , a channel  134 , the drain  84 , and the gate  86 . In some embodiments, the unit pixel  62  may include more than one driving TFT  72  and/or more than one circuit switching TFT  74 . As illustrated, a gate insulator layer  136  is disposed over the source  76 , the channel  132 , and the drain  78  of the driving TFT  72 . Further, the gate insulator layer  136  is disposed over the source  82 , the channel  134 , and the drain  84  of the circuit switching TFT  74 , as represented by block  164  of  FIG. 7 . The gate insulator layer  136  may insulate the channel  134  of the circuit switching TFT  74  from the gate  86  of the circuit switching TFT  74 . 
     As illustrated in  FIG. 6  and represented by block  166  of  FIG. 7 , the gate  86  of the circuit switching TFT  74  is disposed over the gate insulator layer  136  of the circuit switching TFT  74  to control current flow through the channel  134  of the circuit switching TFT  74 . An interlayer dielectric (ILD)  138  is disposed over the gate  86  and the gate insulator layer  136 , as represented by block  168  of  FIG. 7 . A pixel electrode  140  may be disposed along a portion of the ILD  138 , as represented by block  170  of  FIG. 7 . The pixel electrode  140  may be electrically coupled to the drain  78  of the driving TFT  72  by a contact  142  and a via  144 . One or more contacts  142  are disposed over the ILD  138  and electrically coupled to the source  76 , the source  82 , the drain  78 , and the drain  84  by respective vias  144  extending through the ILD  138  and the gate insulator layer  136 . The gate  80  of the driving TFT  72  is disposed over the ILD  138  directly above the channel  132  of the driving TFT  72  to control current flow through the channel  132  of the driving TFT  72 . The vias  144 , contacts  142 , and gate  80  of the driving TFT  72  may be disposed in a single manufacturing step, as represented by block  172  of  FIG. 7 . 
     The gate  80  of the driving TFT  72  is disposed over the ILD  138  and directly above the channel  132  of the driving TFT  72  to provide better voltage control of the driving TFT  72 . A greater distance between the gate  80  of the driving TFT  72  and the channel  132  of the driving TFT  72  may decrease the capacitance formed between the gate  80  and the channel  132  of the driving TFT  72 . This decreased capacitance between the gate  80  and the channel  132  of the driving TFT  72  may use a larger range of voltages applied to the gate  80  to cause a corresponding range of currents to flow through the channel  132  of the driving TFT  72 . A large range of possible input voltages may provide more precise voltage and current control. Moreover, better voltage and current control may provide more accurate gray level control. 
     As represented by block  174  of  FIG. 7 , an insulating layer  146 , such as an organic planarization layer, may be disposed over the ILD  138 , the contacts  142 , the first gate electrode  80  of the driving TFT  72 , and a portion of the pixel electrode  140 . The OLED  88  (e.g. an OLED layer) may be disposed directly over the pixel electrode  140 , as represented by block  176  in  FIG. 7 . In the present embodiment, the display  10  may be a bottom emission display. For example, a top electrode  148  may be disposed over the OLED  88  and the insulating layer  146 , as represented by block  178  of  FIG. 7 . Specifically, the OLED  88  may emit light when current flows between the pixel electrode  140  and the top electrode  148  (e.g., through the OLED  88 ). As may be appreciated, the pixel electrode  140  may comprise a transparent material which transmits the light emitted from the OLED  88 . 
     As mentioned above, by forming the unit pixel  62  as described in  FIGS. 6 and 7 , the pixel aperture ratio may be increased as compared to other designs where circuitry connecting the circuit switching TFT  74  and the driving TFT  72  is disposed in different layers of the unit pixel  62 .  FIG. 8  illustrates a top view of the unit pixel  62  shown in  FIG. 6 . As illustrated, the drain  84  of the circuit switching TFT  74  is electrically coupled to the gate  80  of the driving TFT  72 . As discussed above, the gate  80  is disposed over the ILD  138 . In contrast, the gate  86  is disposed beneath the ILD  138 . The formation of the gate  80  over the ILD  138  may facilitate a connection  160  of the gate  80  to the drain  84  using the contact  142  and the via  144 . As mentioned above, the connection  160  may be formed in the same manufacturing step as the gate  80 , the contacts  142 , and the vias  144  to reduce manufacturing steps. The connection  160  has a width  162  that may be reduced by forming the connection  160  in the same layer as the gate  80 , eliminating additional connection circuitry. For a given unit pixel  62 , reducing the width  162  may facilitate more area for the pixel electrode  140  and the OLED  88  of the display  10 , which may, in turn, increase the aperture ratio of the display  10 . 
     Other embodiments and variations of the embodiments mentioned above may have additional features. For example,  FIG. 9  illustrates a cross-sectional view of another embodiment of a unit pixel  62  of the display  10 . In this embodiment, a dummy gate electrode  164  is disposed over the gate insulator  136  and over the channel  132  of the driving TFT  72 . The dummy gate electrode  164  may act as a doping mask, allowing the source  76  and the drain  78  of the driving TFT  72  to be doped without using a photo resist layer to form a mask. Using the dummy gate electrode  164  as a doping mask may reduce the number of fabrication steps of manufacturing the TFTs  70  of the display  10 . The ILD  138  may also include a raised portion  166  to increase the thickness of the ILD  138  over the dummy gate electrode  164 . 
     A matrix of unit pixels  62  including TFTs  70  manufactured as described above may be manufactured into a display  10  to be used the electronic device  8 .  FIG. 10  illustrates a flowchart  180  of a process for manufacturing an AMOLED display. The matrix of unit pixels  62  may be formed, as described above, to provide the display panel  60 , as represented by block  182 . The display panel  60  may include multiple unit pixels  62  arranged in rows and columns, as illustrated in  FIG. 4 . The processor  16  (e.g., processing device) may be coupled to the display panel  60 , as represented by block  184 . Furthermore, the display panel  60  and the processor  16  may be disposed in a housing of the electronic device  8 , as represented by block  186 . 
     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: 20121102
Publication Date: 20160405
Grant Date: 20160405
Priority Date: 20121102
Inventors: CHANG SHIH CHANG
Chen yu cheng
Assignee: APPLE INC
CPC Classifications: [{"code": "H10D86/431", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D86/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D86/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10D86/431", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L27/1237", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50621873