An in‐cell capacitive touch sensor integrated in an LTPS WSVGA TFT‐LCD

This paper discusses an In‐cell capacitive touch sensor and its integration in an LTPS TFT‐LCD with 7‐inch screen size and WSVGA resolution. The operation of the newly developed sensor is based on capacitive coupling between user's finger and the detection electrode on the TFT substrate, and is purely capacitive. The sensors and the sensor driver circuits have been integrated in the TFT substrate of the prototype TFT‐LCD using LTPS technology. The prototype having 256x150 sensors shows advantages such as smooth operation with no touch force, high position accuracy, multi‐touch (10 or more), a thin and light LCD module, high display quality, and thus is suitable for various applications such as cell‐phones, smart‐phones, mobile‐PCs, and automotive‐use displays.     

A highly sensitive and low‐noise IR photosensor based on a‐SiGe as a sensing and noise filter: Toward large‐sized touch‐screen LCD panels

Abstract— The a‐SiGe TFT photosensor for embedded touch‐screen panels (TSPs) was characterized by comparison with an a‐Si sensor. The photoresponse of an a‐SiGe sensor at a 850‐nm wavelength was much higher than that of a‐Si, indicating that a‐SiGe is a strong candidate material for an IR sensor. In order to increase the signal‐to‐noise ratio, the incident visible light was filtered by incorporating a bandpass‐filter layer. An a‐SiGe IR‐sensor‐embedded LCD panel was successfully demonstrated, showing an excellent multitouch property independent of ambient‐light conditions. This technology can be widely used in multifunctional TSPs.     

Novel LCDs with IR‐sensitive backlights

Abstract— In this paper, a novel multi‐touch LCD architecture with hover‐sensing capability is described. To detect multiple touch points and hover points simultaneously, a sensitive backlight, which is a backlight integrated with an IR sensor array, is introduced. The sensitive backlight uses visible light to display contents on a display screen and is also used to detect reflected IR light from objects on or near the display screen. The captured image from the sensitive backlight is used to extract touch and hover information. The proposed display architecture maintains the slim form factor of an LCD with no loss of display quality, while making it possible to sense multiple touches and hovers simultaneously.     

In‐cell capacitive‐type touch sensor using LTPS TFT‐LCD technology

Abstract— An LTPS TFT‐LCD with an in‐cell capacitive‐type touch sensor has been proposed and prototyped. The embedded sensor in the pixel was designed to amplify the voltage change caused by capacitive coupling between the detection electrode and conductive object (user's finger). No touch force is needed for sensor actuation and no extra electrical connection for the counter‐substrate is needed. The validity of the observed voltage difference of the sensor output on the TFT substrate was examined. The proposed architecture is considered to be applicable to larger LCDs for various applications such as smartphones, automotive navigation systems, and mobile internet devices.     

A 2‐in. a‐Si:H TFT‐LCD with embedded backlight control TFT sensors with various channel widths

Abstract— A 2.0‐in. a‐Si:H TFT‐LCD with embedded TFT sensors for the control of the backlight intensity according to the ambient light intensity has been developed. Two types of a‐Si:H TFT sensors with various channel widths were embedded into a TFT backplane with bottom‐ and top‐gate structures for measuring the ambient light and backlight illumination, respectively. The output signal, measured by a readout IC, increased with backlight intensity until 20,000 lux.     

Development of a 10.4‐in. UXGA display using low‐temperature poly‐Si technology

A new 10.4‐in.‐diagonal display with UXGA resolution (1600 H × 1200 V pixels) using low‐temperature polysilicon (poly‐Si) TFTs has been developed for notebook‐PC applications. The source drive technique uses integrated selector switches, which decreases the number of tape carrier packages (TCPs) for a poly‐Si TFT‐LCD and increases the connection pitch of the TCPs to the glass substrate. In this paper, we present a new display configuration and fabrication process.     

Active‐matrix sensor in AMLCD detecting liquid‐crystal capacitance with LTPS‐TFT technology

Abstract— An active‐matrix capacitive sensor for use in AMLCDs as an in‐cell touch screen has been developed. Pixel sensor circuits are embedded in each pixel by using low‐temperature polycrystalline‐silicon (LTPS) TFT technology. It detects a change in the liquid‐crystal capacitance when it is touched. It is thin, light weight, highly sensitive, and detects three or more touch events simultaneously.     

Ultra‐low‐power LTPS TFT‐LCD technology using a multi‐bit pixel memory circuit

Abstract— Two types of low‐temperature poly‐Si TFT LCDs, which integrate a multi‐bit memory circuit and a liquid‐crystal driver within a pixel, have been developed using two different TFT process technologies. Both a 1.3‐in. 116‐ppi LCD having a 2‐bit pixel memory and a 1.5‐in. 130‐ppi LCD having a 5‐bit pixel memory consume very little power, less than 100 μW, which indicates that this technology is promising for mobile displays.     

Low‐temperature poly‐Si TFT data drivers for an SVGA a‐Si TFT‐LCD panel

Low‐temperature poly‐Si TFT data drivers for an SVGA a‐Si TFT‐LCD panel have been developed. The data drivers include shift registers, sample‐and‐hold circuits, and operational amplifiers, and drive LCD panels using a line‐at‐a‐time addressing method. To reduce the power consumption of the shift register, a dot‐clock control circuit has been developed. Using this circuit, the power consumption of the shift register has been reduced to 36% of that of conventional circuits. To cancel the offset voltage generated by the operational amplifier, an offset cancellation circuit for low‐temperature poly‐Si TFTs has been developed. This circuit is also able to avoid any unstable operation of the operational amplifier. Using this circuit, the offset voltage has been reduced to one‐third of the value without using the offset cancellation circuit. These data drivers have been connected to an LCD panel and have realized an SVGA display on a 12.1‐in. a‐Si TFT‐LCD panel.     

Requirements for large‐sized high‐resolution TFT‐LCDs

Abstract— A 22‐in. prototype TFT‐LCD with a resolution of 200 pixels per inch and wide‐viewing‐angle capability has been developed and its requirements in terms of screen quality and technology will be discussed. An in‐plane‐switching mode with dual‐domain structure, post‐spacers, and high‐resolution process were implemented to achieve superior front‐of‐screen quality. And, also, in order to improve reliability and productivity, we developed a new injection method for liquid crystals which enabled us to eliminate injection holes.     

Active‐matrix organic light‐emitting displays employing two thin‐film‐transistor a‐Si:H pixels on flexible stainless‐steel foil

Abstract— An active‐matrix organic light‐emitting diode (AMOLED) display driven by hydrogenated amorphous‐silicon thin‐film transistors (a‐Si:H TFTs) on flexible, stainless‐steel foil was demonstrated. The 2‐TFT voltage‐programmed pixel circuits were fabricated using a standard a‐Si:H process at maximum temperature of 280°C in a bottom‐gate staggered source‐drain geometry. The 70‐ppi monochrome display consists of (48 × 4) × 48 subpixels of 92 ×369 μm each, with an aperture ratio of 48%. The a‐Si:H TFT pixel circuits drive top‐emitting green electrophosphorescent OLEDs to a peak luminance of 2000 cd/m².     

Development of rapid thermal processor for large‐glass LTPS production

Abstract— A field‐enhanced rapid‐thermal‐processor (FE‐RTP) system that enables LTPS LCD and AMOLED manufacturers to produce poly‐Si films at low cost, high throughput, and high yield has been developed. The FE‐RTP allows for diverse process options including crystallization, thermal oxidation of gate oxides, and fast pre‐compactions. The process and equipment compatibility with a‐Si TFT manufacturing lines provides a viable solution to produce poly‐Si TFTs using a‐Si TFT lines.     

Compact modeling of amorphous‐silicon thin‐film transistors with BSIM3

Abstract— A novel approach of modeling a‐Si:H TFTs with the industry‐standard BSIM3 compact model is presented. The described approach defines the a‐Si:H TFT drain current and terminal charges as explicit functions of terminal voltages using a minimum set of BSIM3 parameters. The set of BSIM3 parameters is chosen based on the electrical and physical characteristics of the a‐Si:H TFT and their values extracted from measured data. By using the selected BSIM3 model parameters, the a‐Si:H TFT is simulated inside SPICE to fit the simulated I‐V and C‐V curves with the measured results. Finally, the extracted BSIM3 model is validated by simulating the kickback voltage effect in an AMLCD pixel array.     

Flexible amorphous‐silicon non‐volatile memory

Abstract— The development of a flexible, rewritable, non‐volatile memory (NVM) that is implemented on a standard, low‐temperature a‐Si:H process without additional mask steps is reported. This NVM is a part of a flexible‐display system. Each NVM cell is composed of differentially configured thin‐film‐transistors (TFTs). The cell reads out one of two stable states depending on the relative threshold voltages of the differentially configured TFTs. Information is stored in each cell by increasing the threshold voltage of one differential TFT or the other, utilizing the well‐known electrical‐stress degradation intrinsic to a‐Si:H TFTs. The stored information is retained indefinitely with no applied power. A test array of individually addressable NVM cells has been successfully fabricated and tested on flexible stainless‐steel substrates. Read and write operation, as well as preliminary reliability measurements, are described. The design is readily scalable to large memory arrays.     

Latest developments for “system‐on‐glass” displays using low‐temperature poly‐Si TFTs

Abstract— A 2.3‐in.‐diagonal QVGA‐formatted “System‐On‐Glass” display has been developed by using low‐temperature poly‐Si TFT‐LCD technology. This display fully integrates 6‐bit RGB digital interface drivers as well as all the power supply circuitry to drive the LCD, which requires neither external driver ICs nor power‐supply ICs. This paper discusses the newly developed TFT circuit technologies used in this LCD. The development trend of the “System‐On‐Glass” display is also reviewed.     

A touch‐sensitive display with embedded hydrogenated amorphous‐silicon photodetector arrays

Abstract— A new touch‐sensitive hydrogenated amorphous‐silicon (a‐Si:H) display with embedded optical sensor arrays is presented. The touch‐panel operation was successfully demonstrated by fabricating a prototype of a 16‐in. active‐matrix liquid‐crystal display (AMLCD). The proposed system, obviating the need for the extraction of information from the captured images in real time, provides the location of the finger touch. Due to the simple architecture of the system, the touch‐panel operation can be readily integrated within large‐area displays.     

Thermal dimensional stability of glass substrates for poly‐Si TFT‐LCD application

Abstract— Thermal dimensional stability of Fusion‐drawn Corning Code 1737 glass was investigated at simulated thermal cycles for low‐temperature poly‐Si TFT fabrication. For low‐temperature poly‐Si TFT processes between 550 and 600°C, annealed Code 1737 is required to meet a typical thermal shrinkage requirement of less than 20 ppm. For super‐low‐temperature poly‐Si TFT processes between 400 and 450°C, Code 1737 meets the requirement in the unannealed state. Code 1737 glass having a high strain point of 666°C provides thermal capabilities as a substrate for low‐temperature poly‐Si TFT‐LCD applications.     

Low‐power‐consumption TFT‐LCD with dynamic memory embedded in the pixels

A low‐power‐consumption thin‐film‐transistor liquid‐crystal display (TFT‐LCD) with dynamic memory cells embedded in each pixel using low‐temperature poly‐Si technology has been developed. By holding data in the memory, the operating rate of the data driver can be dramatically reduced to 4 Hz. Eight levels of gray scale with low power consumption can be achieved by using the area‐ratio gray‐scale method. This TFT‐LCD can be used for displaying fine still images, with low power consumption.     

A new a‐Si:H TFT pixel circuit employing data‐reflected negative‐bias annealing for a stable and uniform AMOLED

Abstract— A new a‐Si:H pixel circuit to reduce the VTH degradation of driving a‐Si:H thin‐film transistors (TFTs) by data‐reflected negative‐bias annealing (DRNBA) is presented. The new pixel circuit compensates VTH variation induced by non‐uniform degradation of each a‐Si:H pixel due to various electrical stress. The proposed pixel circuit was verified by SPICE simulations. Although the VTH of the driving a‐Si:H TFT varies from 2.5 to 3.0 and 3.5 V, the organic light‐emitting diode (OLED) current changes by only 1.5 and 2.8% in the emission period, respectively. During the negative‐bias annealing period, the negative VGS is applied to the driving TFT by using its own data signal. It is expected that the VTH shift of the driving TFT can be effectively reduced and the VTH shift can be compensated for in our new pixel circuit, which can contribute to a stable and uniform image from an a‐Si:H TFT active‐matrix OLED.     

Current status and future prospect of in‐cell‐polarizer technology

Abstract— A thin‐crystalline‐film (TCF) polarizer has been developed which can be used internally in liquid‐crystal‐display cells. Based on this material, a manufacturing process has been developed for the fabrication of monochrome LCDs with internal polarizers. A new TCF polarizer material and coating equipment, developed to realize a high‐performance color TFT‐LCD, are discussed.