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.     

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.     

A novel low‐power‐consumption all‐digital system‐on‐glass display with serial interface

Abstract— A new conceptual ultra‐compact LCD panel, which features a simple interface and lower‐power consumption by using low‐temperature polysilicon thin‐film transistor (LTPS‐TFT) technology has been developed. This panel is capable of switching operation modes based on an input command, and all the data are directly communicated with the circuit inside the panel through a Serial Peripheral Interface (SPI) protocol. The integration of the serial‐data‐receiver function on glass substrate has enabled the achievement of a significant reduction in the number of interface pins. Moreover, a low power consumption of 15 μW for a 2.26‐in. reflective LCD panel in combination with the technique of integrating a memory circuit in each pixel has been achieved.     

LTPS circuit integration for system‐on‐glass LCDs

Abstract— A 3.5‐in. QVGA‐formatted driving‐circuit fully integrated LCD has been developed using low‐temperature poly‐Si (LTPS) technology. This display module, in which no external ICs are required, integrates all the driving circuits for a six‐bit RGB digital interface with an LTPS device called a “FASt LDD TFT” and achieves a high‐quality image, narrow frame width, and low power consumption. The LTPS process, device, and circuit technologies developed for system‐on‐glass LCD discussed. The development phase of LTPS circuit integration for system‐on‐glass LCDs is also reviewed.     

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.     

Digital‐to‐analog converter with gamma correction on glass substrate for TFT‐panel applications

Abstract— Low‐temperature polysilicon (LTPS) technology has a tendency towards integrating all circuits on glass substrate. However, the poly‐Si TFTs suffered poor uniformity with large variations in the device characteristics due to a narrow laser process window for producing large‐grained poly‐Si TFTs. The device variation is a serious problem for circuit realization on the LCD panel, so how to design reliable on‐panel circuits is a challenge for system‐on‐panel (SOP) applications. In this work, a 6‐bit R‐string digital‐to‐analog converter (DAC) with gamma correction on glass substrate for TFT‐panel applications is proposed. The proposed circuit, which is composed of a folded R‐string circuit, a segmented digital decoder, and reordering of the decoding circuit, has been designed and fabricated in a 3‐μm LTPS technology. The area of the new proposed DAC circuit is effectively reduced to about one‐sixth compared to that of the conventional circuit for the same LTPS process.     

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.     

Ultra‐low‐power polysilicon AMLCD with full integration

Abstract— An LTPS TFT‐LCD that only consumes 0.07 mW of power was developed. It is the world's first LCD equipped with all the circuits needed to display still images continuously for up to 1 year on a button battery. At the same time, the panel is capable of displaying 260,000‐color moving pictures.     

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.     

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.     

Low‐temperature poly‐Si TFT‐LCD with an integrated analog circuit

We have developed a 6‐bit D/A converter and amplifier integrated low‐temperature poly‐Si TFT‐LCD in which an integrated signal‐line driver is driven by a 5‐V power supply. We have employed a D/A converter including a new capacitor array and an original amplifier comprised of serially connected comparators to achieve high accuracy. The D/A converter performs gamma correction using upper significant bits of input data. Control signals for these circuits were generated by the integrated timing circuit. These advances in integration have been achieved for the first time using 3‐μm design rule and improved LTPS TFT technologies and provide an advanced display system with lower power consumption, smaller module size, and higher durability.     

A new low‐power driving method for high‐resolution mobile IPS LCDs

Abstract— High‐resolution displays are now needed for mobile equipment, not only for cell phones but for other devices such as ultra‐mobile PCs (UMPCs) and mobile Internet protocol televisions (IPTVs). A new low‐cost and low‐power driving method for high‐resolution in‐plane‐switching (IPS) liquid‐crystal displays (LCDs) on a low‐temperature polycrystalline‐silicon (LTPS) thin‐film‐transistor (TFT) platform has been developed. Because this method drives common electrodes separated by each line, it can reduce inversion frequency, unlike “dot‐inversion” or “column‐inversion” methods. On the other hand, it was found that horizontal smear is an obstacle to achieve this method. To solve this problem, techniques to optimize the timing of RGB time‐sharing are proposed. A 5‐in. WXGA (1366 × 768) prototype using the new driving method was fabricated, and it was found that the horizontal smear is less than ±1% of the luminance and that the power consumption of the display discharge and charge is 0.245 W.     

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.     

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.     

New approaches to process simplification for large‐area high‐resolution TFT‐LCDs

Abstract— Novel process architectures are proposed for fabricating large‐area high‐resolution TFT‐LCDs with a minimal number of process steps. A low contact resistance between Al bus lines and the transparent conductive oxide layer, necessary for large‐area panels, is obtained by inducing a self‐formed inter‐metallic compound layer at the interface without using any additional buffer or capping layers. For enhanced brightness and resolution, a new TFT array structure integrated on a color‐filter substrate, referred to as an Array on Color Filter (AOC) structure, has been developed. Good‐quality TFTs were successfully constructed on the newly developed color filter for AOC within a sufficiently wide process margin. By adopting these novel technologies, a 15.0‐in. XGA prototype panel was fabricated and shows good display performance. Thus, these novel technologies have improved cost efficiency and productivity for TFT‐LCD manufacturing, and can be applied to the development of TFT‐LCDs of extended display area and enhanced resolution, benefiting from the low resistance bus lines, the high aperture ratio, and reduction in total process steps.     

Towards large‐area full‐color active‐matrix printed polymer OLED television

Abstract— We have developed a new multi‐head polymer OLED ink‐jet‐printing technology to make large‐screen OLED television displays. This printer is used to make a 13‐in.‐diagonal 16:9‐format polymer‐OLED prototype driven by an LTPS active matrix with a pixel circuit which compensates for TFT threshold‐voltage variations. A novel scrolling‐bar addressing scheme is used to reduce motion artifacts and to make sparkling images with a high local peak brightness. The scalability of the polymer‐OLED technology to larger sizes for television applications is discussed.     

A high‐aperture‐ratio and low‐crosstalk pixel structure design for in‐plane‐switching‐mode TFT‐LCDs

Abstract— The TFT‐LCD market is growing rapidly, and the replacement of CRT TV by LCD TV requires the implementation of LC modes with wide viewing angles and high brightness. The IPS mode is an excellent technology to realize wide viewing angles, but it has a low aperture ratio that has now been improved by Advanced Super‐IPS (AS‐IPS). In this paper, we propose a novel pixel structure design that not only increases the aperture ratio but also reduces the crosstalk. We have improved the current AS‐IPS aperture ratio by 1.25 times and effectively reduced the capacitive coupling ratio from 1.2% to 0.05%.     

A new pixel design and a novel driving scheme for multi‐domain vertically aligned LCDs

Abstract— By using a new pixel design and a novel driving scheme that adds a bias electrode and a bias TFT to the ordinary pixel structure, a high‐contrast‐ratio and wide‐viewing‐angle LCD mode, refered to as the biased vertical‐alignment (BVA) mode, has been sucessfully developed. Compared to the published data on the PVA and MVA modes, the BVA mode has a distinct advantage of lower manufacturing cost due to the elimination of a lithographic process step that forms either ITO cuts or protrusions on the color‐filter substrates. The BVA mode requires ITO cuts on the TFT substrate similar to that for the PVA and MVA modes. The 15‐in. BVA‐mode XGA prototype exhibits a high contrast ratio of 1200:1 and high cell transmittance of 4.3%.     

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.     

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.