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.     

Development of a 14.1‐in. UXGA TFT‐LCD using LTPS technology

A 14.1‐in. UXGA low‐temperature poly‐Si TFT‐LCD has been developed using p‐MOS technology. Both the peripheral driving circuits and the pixel switches are implemented using only p‐channel TFTs. The device performance for the driving circuits and the panel design issues, such as crosstalk and flicker, were investigated. The image quality required for the notebook‐PC display has been achieved by optimizing the panel design and by improving the device performance. In addition, the redundant gate driving structure has been developed to minimize the degradation of the panel yield.     

A full integration of electromagnetic resonance sensor and capacitive touch sensor into LCD

We have developed a transmissive and reflective LCD that integrates electromagnetic resonance (EMR) and capacitive touch sensors using existing in‐cell process. This development has been achieved by utilizing our hybrid‐in‐cell technology with low resistance material for the RX, which is an improvement of over 80% compared with conventional indium thin oxide (ITO) material. For EMR detection, we have slightly modified the TX layer used for capacitive touch sensing, by making a coil loop that generates a magnetic field on the panel. The direction of current on the coil can be modulated by the low‐temperature polycrystalline silicon (LTPS) circuit. Our in‐cell touch sensing has separately assigned timings for display and touch units. This time‐sharing method provides immunity from display noise and consequently better signal‐to‐noise ratio (SNR) than other out‐cell types. In parallel, we have developed a new controller that can support both EMR and capacitive sensing as a one‐chip solution, with the capability of maximizing signal levels lowering noise and detecting the frequency precisely when there is pressure on the pen tip. Our in‐cell technologies contribute not only a good SNR for EMR pen but also the added benefits for thin design, lightweight panel, compared with conventional LCD techniques.     

Incorporation of input function into displays using LTPS TFT technology

Abstract— A new display in which an input function is incorporated has been developed by using LTPS TFT technology. A new circuit configuration that includes a lateral p‐i‐n diode with an in‐pixel amplifier, an LTPS A/D converter on the periphery of the glass substrate and an external image‐processing LSI is presented. The experimental results of two major applications of the image‐capture function and touch‐panel function are discussed.     

Touch‐screen panel integrated into 12.1‐in. a‐Si:H TFT‐LCD

Abstract— A touch‐screen‐panel (TSP) embedded 12.1‐in. LCD employing a standard existing a‐Si:H TFT‐LCD process has been successfully developed. Compared with conventional external touch‐screen panels, which use additional components to detect touch events, the new internal TSP exhibits a clearer image and improved touch feeling, as well as increased sensing speed using discrete sensing lines to enable higher‐speed sensing functions including handwriting. The new internal digital switching TSP can be fabricated with low cost because it does not require any additional process steps compared to a standard a‐Si:H TFT‐LCD.     

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.     

Improved image quality of a high‐transflective tRGB‐t/rW TFT‐LCD

Abstract— This work combines a very simple resolution rescaling method, a well‐known RGB‐to‐YUV converting technique and a detection strategy into an optimized switchable mechanism in order to eliminate the problems of obvious zigzag profiles caused by the special layouts of transflective tRGB‐t/rW TFT‐LCDs and the poor reflective gray‐level contrast ratio effected by the minimum white data in the transmissive RGB‐W + subpixel rendering algorithms. Finally, a transflective tRGB‐t/rW TFT‐LCD is revealed not only to have no visible zigzag profiles and high visibility of reflective gray‐level contrast ratio, but also to have extreme reflectance and transmittance. The excellent optical performance of the proposed system makes it particularly suitable for single‐panel applications that need both high‐transmissive main displays and high‐reflective subdisplays.     

Flexible OLED display with 620°C LTPS TFT and touch sensor manufactured by weak bonding method

By weak bonding method, the first organic light‐emitting diode (OLED) display with 620°C low‐temperature poly‐silicon (LTPS) thin film transistor (TFT) and touch sensor, without polyimide (PI) substrate, formed on glass substrates is transferred to non‐PI flexible substrates. After transfer, the display image is free from defect, and touch sensor functions normally. Compared with device made on PI substrate, the advantages of device stability and pitch variation by transferring are shown.     

Electrical models of TFT‐LCD panels for circuit simulations

Abstract— As thin‐film‐transistor liquid‐crystal‐display (TFT‐LCD) panels become larger and provide higher resolution, the propagation delay of the row and column lines, the voltage modulation of Vcom, and the response time of the liquid crystal affect the display images now more than in the past. It is more important to understand the electrical characteristics of TFT‐LCD panels these days. There are several commercial products that simulate the electrical and optical performance of TFT‐LCDs. Most of the simulators are made for panel designers. However, this research is for circuit, system, and panel designers. It is made in a SPICE and Cadence environment as a commercial circuit‐design tool. For circuit and system designers, it will help to design the circuit around a new driving method. Also, it can be easily modified for every situation. It also gives panel designers design concepts. This paper describes the electrical model of a 15‐in. XGA (1024 × 768) TFT‐LCD panel. The parasitic resistance and capacitance of the panel are obtained by 3‐D simulation of a subpixel. The accuracy of these data is verified by the measured values of an actual panel. The developed panel simulation platform, the equivalent circuit of a 1 5‐in. XGA panel, is simulated by HSPICE. The results of simulation are compared with those of experiment, according to changing the width of the OE signal. The proposed simulation platform for modeling TFT‐LCD panels can be especially applied to large‐sized LCD TVs. It can help panel and circuit designers to verify their ideas without making actual panels and circuits.     

Value‐added integration of functions for silicon‐on‐glass (SOG) based on LTPS technologies

Abstract— Low‐temperature polycrystalline‐silicon (LTPS) TFT‐LCDs are on their way to becoming advanced displays, which will lead to the use of system‐on‐glass (SOG) technology. Improvement in poly‐Si TFT performance is essential in order for them to become value‐added displays, where circuits for various functions are integrated onto the substrate. In this paper, the key processes of the applications for future displays will be described, including the recent development of SOG.     

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.     

Super‐large‐sized TFT‐LCD (55 in.) for HDTV application

Abstract— We have developed the world's largest TFT‐LCD, which has a 55‐in.‐diagonal size. This LCD features a 1920 × 1080 (16:9) resolution for full‐HDTV images, 500‐nit luminance, 72% color gamut, and 12‐msec response time at all gray levels. The size of the panel (55 in.) was determined by the maximum efficiency of our fifth‐generation line (glass size: 1100 × 1250 mm). To overcome the limitation of size in photolithography equipment, a new stitcking‐free technology was applied in both the TFT and color‐filter side. And the super‐IPS mode was used as a wide‐viewing‐angle technology because it is suitable in the fabrication of large panels. In this paper, we present issues on both the fabrication and characteristics of the 55‐in. TFT‐LCD.     

TFT‐LCD driver IC with embedded non‐volatile memory for portable applications

Abstract— To improve the display quality and yield of the TFT‐LCD driver IC, non‐volatile multiple‐time‐programmable (MTP) memory, which consists of an EEPROM cell and our proposed sense amplifier and power control circuit (SP), was integrated into a TFT‐LCD driver IC. The proposed SP has a 30% smaller layout area and a 18% faster response time compared to that of the conventional SP. The proposed SP also has lower power consumption because it does not use a static current. The TFT‐LCD quality was also improved by tuning the characteristics of the driver IC and the panel with the VREF, OSC, and VCOM blocks, using non‐volatile MTP memory. When the display quality improved, the yield also improved, along with a reduction in the failure ratio of the display module, which consists of the driver IC and the panel. As a result, the TFT‐LCD driver IC with the non‐volatile MTP memory demonstrated improved display quality and a higher yield compared to conventional driver ICs without such a memory.     

A study of roll‐printing technology for TFT‐LCD fabrication

Abstract— Recently, potential breakthrough technologies for low‐cost processing of TFT‐LCDs and new process developments for flexible‐display fabrication have been widely studied. A roll‐printing process using etch‐resist material as a replacement for photolithographic patterning was investigated. The characterization of the properties of patterns formed in roll printing, a method to fabricate cliché plates for fine patterns, and the design of a new formulation for resist printing ink is reported. The pattern position accuracy, which is one of the most important issues for the successful application of printing processes in display manufacturing was studied and how it can be improved by optimizing the blanket roll structure is explained. New design rules for the layout of the thin‐film‐transistor array was derived to improve the compatibility of roll printing. As a result, a prototype 15‐in.‐XGA TFT‐LCD panel was fabricated by using printing processes to replace all the photolithographic patterning steps conventionally used.     

Novel LTPS technology for large substrate

We developed partial laser anneal silicon (PLAS) thin‐film transistor (TFT) of novel low‐temperature polycrystalline‐silicon (LTPS) technology, which had the mobility of 28.1 cm²/Vs lager than that of mass produced oxide TFT and photo‐stability comparable with that of LTPS TFT in bottom gate structure. This innovative technology enables the conversion from an α‐Si TFT to a high‐mobility TFT most easily and inexpensively. Moreover, there is no limit of substrate size, such as Gen10 and more. Photo‐stability of PLAS will be suitable to organic light‐emitting diode backplane, high‐dynamic range TV, and outdoor IDP.     

Novel mobile TFT‐LCDs based on SLS technology

Abstract— Single‐crystal‐like silicon (SLS) technology is the most cost‐effective laser‐crystallization process ever invented. The throughput of the SLS process is about two times higher than that of the conventional excimer‐laser annealing (ELA) method. In addition, the performance of the TFTs fabricated by the SLS process is among the best utilized in mass production. Various TFT‐LCDs employing SLS technology, which included a 1.02‐in. full SOG LCD using an icon display for the sub‐display of cellular phones, a 1.9‐in. qVGA TFT‐LCD with a low‐power analog interface employing a low‐voltage driving scheme, and a 3.0‐in. VGA TFT‐LCD compatible with the 480i data format without additional signal processing were developed. Because the SLS process enables us to achieve highly uniform and reliable transistors, it can be effectively utilized in the mass production of mobile TFT‐LCDs with low power consumption and enhanced image quality.     

Development of middle size full in‐cell LCD module for PC with IGZO

We developed the world's first middle size full in‐cell LCD for PC with IGZO technology. We evaluated a new Gate driver In Panel structure with latch circuit and confirmed that there were no problems with display and touch panel performance. Furthermore, we did a feasibility study of higher display resolutions and larger size panels, which showed future possibilities.     

Ultra‐FFS TFT‐LCD with super image quality,fast response time,and strong pressure‐resistant characteristics

Fringe‐field‐switching (FFS) devices using liquid‐crystal (LC) with a negative dielectric anisotropy exhibit high transmittance and wide viewing angle simultaneously. Recently, we have developed an “Ultra‐FFS” thin‐film‐transistor (TFT) LCD using LC with a positive dielectric anisotropy that exhibits high transmittance, is color‐shift free, has a high‐contrast ratio in a wide range, experiences no crosstalk and has a fast response time of 25 msec. In this paper, the device concept is discussed, and, in addition, the pressure‐resistant characteristics of the devices compared with that of the twisted‐nematic (TN) LCD is discussed.     

Thermal‐deformation characterization on the panel of TFT‐LCD TV. Part I: Mechanism of color distortion

Abstract— In this study we applied both numerical simulation and experimental validation to characterize the thermal deformation of the panel and the direct‐lit backlight unit (BLU) of a thin‐film‐transistor liquid‐crystal‐display television (TFT‐LCD TV). Heat emitted from cold‐cathode fluorescent lamps (CCFLs) causes thermal deformation of the LCD and extrudes the panel from the metal front shield at both upper corners: this finally leads to color distortion. In the numerical simulation based on thermal‐fluidic fields of the TFT‐LCD TV, natural convection of air that surrounded the CCFLs resulted in a high temperature at the upper‐right and upper‐left corners of the LCD panel. Numerical results were verified by temperature measurements with good consistency. Additionally, this study has established a measurement system to characterize the temperature distribution on both the BLU and panel and the thermal deformation of the panel causing the color distortion.     

A 470 × 235‐ppi poly‐Si TFT‐LCD for high‐resolution 2‐D and 3‐D autostereoscopic displays

Abstract— We have developed a 470 × 235‐ppi poly‐Si TFT‐LCD with a novel pixel arrangement, called HDDP (horizontally double‐density pixels), for high‐resolution 2‐D and 3‐D autostereoscopic displays. 3‐D image quality is especially high in a lenticular‐lens‐equipped 3‐D mode because both the horizontal and vertical resolutions are high, and because these resolutions are equal. 3‐D and 2‐D images can be displayed simultaneously in the same picture. In addition, 3‐D images can be displayed anywhere and 2‐D characters can be made to appear at different depths with perfect legibility. No switching of 2‐D/3‐D modes is necessary, and the design's thin and uncomplicated structure makes it especially suitable for mobile terminals.