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.     

Implementation of delta—sigma analog‐to‐digital converter in LTPS process

Abstract— An on‐panel delta—sigma analog‐to‐digital converter (ADC) has been implemented and verified for 3‐μm low‐temperature polysilicon (LTPS) technology with two basic blocks: a delta—sigma modulator and a decimation filter. From the experimental results, the digital output from the delta—sigma modulator is correctly matched with the analog input voltage ratio such that the digital output can be converted into 8‐bit digital code successfully under a supply voltage of 10 V from the decimation filter. The implemented on‐panel delta—sigma ADC can be used for the application of temperature‐to‐digital converter on glass substrate.     

Toward sub‐micron oxide thin‐film transistors for digital holography

High‐performance 2‐μm‐channel oxide thin‐film transistors (TFT) on glass substrate for a 7‐μm‐pixel‐pitch spatial light modulator panel for digital holography applications were fabricated using a two‐step source/drain etching process. It showed a μ_FE of 45.5 cm²/Vs, SS of 0.10 V/dec, and Von of near zero voltage. Furthermore, we succeeded in the demonstration of sub‐micron TFTs, which is an indispensable route to next‐generation spatial light modulation devices with near 1‐μm pixel pitch. The issue of short‐channel transistors for display applications is also introduced. Finally, the digital holographic demonstration results based on the fabricated backplane are presented.     

Peripheral circuit designs using low‐temperature p‐type poly‐Si thin‐film transistors

Abstract— P‐type low‐temperature (450°C) polycrystalline‐silicon thin‐film‐transistor circuits for peripheral driver integration in active‐matrix displays are proposed and verified. A low‐voltage (5 V) driven poly‐Si scan driver is designed by employing a level shifter and shift register. A source driver for six‐bit digital interface is proposed, and the building blocks such as latch, DAC, and analog buffer are described. The latch samples and holds the digital bits (D and D') without an output voltage loss. A new source‐follower type analog buffer is developed and exhibits a small offset deviation regardless of the V_TH variation of the buffer TFT. The simulation and measurement results ensure that the proposed circuits were successfully designed for p‐type panel integration.     

Organic light‐emitting diodes with enhanced out‐coupling efficiency using high‐refractive‐index glass frit

We have fabricated a novel type of substrate for organic light‐emitting diodes (OLEDs) to improve the light out‐coupling efficiency. It was fabricated by forming an excellent flat layer using a high‐refractive‐index B₂O₃‐SiO₂‐Bi₂O₃ frit glass on the light diffusive glass substrate. By using this substrate, we have sufficiently reduced the total internal reflection of OLEDs, and we successfully obtained more than 1.9 times higher light out‐coupling efficiency without spectral changes and viewing angle dependency. Furthermore, we have also successfully demonstrated 50 × 50 mm large‐area white OLEDs with this novel substrate.     

Effects of localized warpage and stress on chip‐on‐glass packaging: Induced light‐leakage phenomenon in mid‐sized TFT‐LCD

Abstract— Mura defects become visible in a 13.3‐in. TFT‐LCD using chip‐on‐glass (COG) packaging when the thickness of the glass substrate is decreased from 0.5 to 0.3 mm. Mura, the non‐uniform brightness in LCDs, is caused by COG packaging due to the mismatch of the coefficient of thermal expansion (CTE) and Young's modulus between the glass substrate and the IC‐driver Si chips. In this paper, a 3‐D finite‐element‐analysis (FEA) model, coupled with transient thermal analysis is first established to examine the warpage and stress behavior in the upper‐glass‐plate post‐COG‐package processing for identifying the root causes of the light‐leakage phenomenon. Prior to that, the simulated warpage results are validated by surface‐contour measurement. Data and modeling results show that a low bonding temperature together with a low modulus in novel ACF materials can effectively eliminate Mura. Besides, thinner silicon or a shorter length of Si chips as drivers offers enhanced reduction in the localized warpage, and thus can be a practical and low‐cost solution for eliminating mura defects.     

Switchable transmissive and reflective liquid‐crystal display using a multi‐domain vertical alignment

Abstract— A wide‐view transflective liquid‐crystal display (LCD) capable of switching between transmissive and reflective modes in response to different ambient‐light conditions is proposed. This transflective LCD adopts a single‐cell‐gap multi‐domain vertical‐alignment (MVA) cell that exhibits high contrast ratio, wide‐viewing angle, and good light transmittance (T) and reflectance (R). Under proper cell optimization, a good match between the VT and VR curves can also be obtained for single‐gamma‐curve driving.     

Resolution enhancement of integral‐imaging three‐dimensional display using directional elemental image projection

Abstract— A new approach to resolution enhancement of an integral‐imaging (II) three‐dimensional display using multi‐directional elemental images is proposed. The proposed method uses a special lens made up of nine pieces of a single Fresnel lens which are collected from different parts of the same lens. This composite lens is placed in front of the lens array such that it generates nine sets of directional elemental images to the lens array. These elemental images are overlapped on the lens array and produce nine point light sources per each elemental lens at different positions in the focal plane of the lens array. Nine sets of elemental images are projected by a high‐speed digital micromirror device and are tilted by a two‐dimensional scanning mirror system, maintaining the time‐multiplexing sequence for nine pieces of the composite lens. In this method, the concentration of the point light sources in the focal plane of the lens array is nine‐times higher, i.e., the distance between two adjacent point light sources is three times smaller than that for a conventional II display; hence, the resolution of three‐dimensional image is enhanced.     

Digital time‐modulation pixel memory circuit in LTPS technology

Abstract— A digital time‐modulation pixel memory circuit on glass substrate has been designed and verified for a 3‐μm low‐temperature polysilicon (LTPS) technology. From the experimental results, the proposed circuit can generate 4‐bit digital codes and the corresponding inversion data with a time‐modulation technique. While the liquid‐crystal‐display (LCD) panel operates in the still mode, which means the same image is displayed on the panel, a data driver for an LCD panel is not required to provide the image data of the frame by the proposed pixel memory circuit. This pixel memory circuit can store the frame data and generate its corresponding inversion data to refresh a static image without activating the data driver circuit. Therefore, the power consumption of a data driver can be reduced in the LCD panel.     

Trench‐type deep N‐well dual guard ring for the suppression of substrate noise coupling

This article presents a study on the isolation performance of the trench‐type deep n‐well (DNW) dual guard ring (GR) and its effect on the suppression of the substrate digital noise coupling on a low noise amplifier (LNA) based on measurement and TCAD simulation. The trench‐type DNW dual GR, in which the DNW is formed beneath the ring‐shaped n‐well region only, can be adopted for protecting the noise‐sensitive analog/RF circuits or circuit blocks against the substrate noise. An in‐depth analysis on the performance of the trench‐type DNW was carried out based on both measurement and a heavy use of TCAD. The results show that the trench‐type DNW dual GR exhibits comparable isolation to that of the pocket‐type DNW dual GR at high frequency regime. The effect of various GR dimension parameters and GR bias conditions on the GR isolation performance was also investigated and analyzed. Furthermore, the trench‐type DNW dual GR was applied to a 5.8‐GHz LNA and its effect on the suppression of the substrate digital noise coupling was studied for various digital noise conditions and GR bias schemes. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

10‐bit source driver with resistor‐resistor‐string digital‐to‐analog converter

Abstract— A 10‐bit gray‐scale source driver using a resistor‐resistor‐string digital‐to‐analog converter (RR‐DAC) is proposed for a TFT‐LCD source driver. The 10‐bit RR‐DAC consists of an 8‐bit resistor‐string DAC and a two‐bit resistor‐string DAC without an intermediate unity‐gain buffer to isolate the parallel‐connected resistor string. The output deviation of the proposed source driver is less than ±3 mV. The chip area of the proposed 10‐bit source driver with an RR‐DAC is increased to 29% of that of an 8‐bit source driver.     

Study on wet patterning of thin films in vertical‐transfer wet station for thin‐film‐transistor manufacturing

Abstract— To overcome the “pseudo‐puddling effect” in a low‐angle‐tilt transfer system with an oversized glass substrate over 2 m, a vertical transfer is suggested. The aim of the present work is to study the wet‐etching behavior of an aluminum/molybdenum double layer deposited on the glass substrate in a vertical transfer wet etching system and compare it with a typical 5°‐tilt‐transfer system. Compared with the tilt‐transfer wet station, the vertical etching system has three advantages, namely, 50% space savings, higher throughput due to the high etch rate, and good etch uniformity over the entire glass for thin‐film‐transistor application. The computational fluid‐dynamics analysis is used to predict the change of the etch uniformity as a function of the tilt angle of the glass substrate.     

Metasurface‐based low‐profile high‐gain substrate‐integrated Fabry‐Pérot cavity antenna

A metasurface‐based substrate integrated Fabry‐Pérot cavity (FPC) antenna is presented for improved radiation performance associated with the low profile. A novel partially reflective planar (PRS) artificial magnetic conductor (AMC) structure is proposed as the upper reflector of the substrate integrated FP resonant cavity. A microstrip patch antenna is embedded inside the cavity as a feed. The proposed antenna is designed to operate at 9.35 GHz with the maximum realized gain of 14.2 dBi and the overall profile of λ₀/10 (λ₀ is the operating wavelength in free space). The low‐profile performance of the proposed design outperforms any previous substrate‐integrated FPC antenna design with this gain performance. The influences of the FP cavity on the reduction of the antenna profile and the enhancement of the antenna gain are also investigated. Good agreement between the measured and simulated results validates the feasibility of the analysis and design approach.     

An area‐ratio gray‐scale method to achieve image uniformity in TFT‐LEPDs

Abstract— An area‐ratio gray‐scale method (ARG) has been developed for low‐temperature‐polysilicon thin‐film‐transistor‐driven light‐emitting‐polymer displays (LTPS TFT‐LEPDs). A pixel consists of plural sub‐pixels, which are controlled to be in either an on‐state or off‐state. The gray scale is acquired by selecting the number of the on‐state sub‐pixels, that is, the ratio of the light‐emitting area. One advantage of the ARG is to improve image uniformity. In the on‐state, since TFT resistance is negligible, the current is determined by the LEP diode resistance. Therefore, the TFT characteristic deviation has no effect on the current. Moreover, the dimensions of each sub‐pixel are the same, and the shapes of the sub‐pixel are circular in order to improve their uniformity. As a result, the image becomes uniform. Another advantage of the ARG is to achieve digital operation, which makes interfacing easy. A digital‐analog converter (DAC) automatically exists in the sub‐pixel and the naked eye.     

Design and implementation of readout circuit on glass substrate with digital correction for touch‐panel applications

Abstract— A readout circuit on glass substrate with digital correction, which contains a transconductance amplifier, counter, and digital correction circuit, has been designed for touch‐panel applications for 3‐μm low‐temperature polysilicon (LTPS) technology. The voltage difference as a result of a change in capacitance due to a touch event is converted to current by a transconductance amplifier. By charging and discharging the capacitor in the counter, the counter displays different digital‐output codes according to touch or non‐touch events. Furthermore, not only can the touch or non‐touch event be distinguished, but also the influence of LTPS process variation can be compensated by a digital correction circuit in the proposed readout circuit.     

Multirate sampled‐data stabilization for a class of low‐order lower‐triangular nonlinear systems

This paper investigates the problem of sampled‐data controller design for a class of lower‐triangular systems in the p‐normal form (0<p<1). A multirate digital feedback control scheme is proposed to achieve the global strong stabilization of the sampled‐data closed‐loop system under some assumptions. In the design of the controller, the input‐Lyapunov matching strategy and multirate control approach are combined to obtain better stabilizing performance. Unlike the design method based on the approximate discrete‐time model, our controller is obtained from the exact discrete‐time equivalent model, which does not need to be computed completely. The approximate multirate digital controllers are proved to be effective in the practical implementation. It is shown that, compared with the emulated control scheme, our controller may provide faster decrease of Lyapunov function for each subsystem. This will lead to allow large sampling periods. An illustrative example is provided to verify the effectiveness of the proposed control scheme.     

A digitally driven pixel circuit with current compensation for AMOLED microdisplays

A novel digitally driven pixel circuit for active‐matrix organic light‐emitting diode (OLED) microdisplays is proposed and evaluated. This circuit supports both pulse width modulation and pulse density modulation digital drive approaches. Only three transistors and one capacitor are required per pixel for the proposed circuit. A current mirror is used to compensate for the pixel current changes that occur because of the degradation of the OLEDs over time. The compensation current depends on the potential of the common cathode, the properties of the current mirror, and the Width/Length (W/L) ratio of the drive transistor. The proposed digital pixel circuit also has advantages in circuit layout compared with analog pixel circuits.     

Silicon‐nanocrystal‐based photosensor integrated on low‐temperature polysilicon panels

Abstract— A photodetector using a silicon‐nanocrystal layer sandwiched between two electrodes is proposed and demonstrated on a glass substrate fabricated by low‐temperature poly‐silicon (LTPS) technology. Through post excimer‐laser annealing (ELA) of silicon‐rich oxide films, silicon nanocrystals formed between the bottom metal and top indium thin oxide (ITO) layers exhibit good uniformity, reliable optical response, and tunable absorption spectrum. Due to the quantum confinement effect leading to enhanced phonon‐assisted excitation, these silicon nanocrystals, less than 10 nm in diameter, promote electron‐hole‐pair generation in the photo‐sensing region as a result resembling a direct‐gap transition. The desired optical absorption spectrum can be obtained by determining the thickness and silicon concentration of the deposited silicon‐rich oxide films as well as the power of post laser annealing. In addition to obtaining a photosensitivity comparable to that of the p‐i‐n photodiode currently used in LTPS technology, the silicon‐nanocrystal‐based photosensor provides an effective backlight shielding by the bottom electrode made of molybdenum (Mo). Having a higher temperature tolerance for both the dark current and optical responsibility and maximizing the photosensing area in a pixel circuit by adopting a stack structure, this novel photosensor can be a promising candidate for realizing an optical touch function on a LTPS panel.     

STATE‐SPACE DIGITAL PID CONTROLLER DESIGN FOR MULTIVARIABLE ANALOG SYSTEMS WITH MULTIPLE TIME DELAYS

This paper presents a discrete‐time state‐space methodology for optimal design of digital PID controllers for multivariable analog systems with multiple time delays. The multiple time‐delayed multivariable analog systems are formulated in a state‐space generic form so that the exact discrete‐time state‐space model can be constructed. Then, the optimal digital PID controller is designed via a state‐feedback and state‐feedforward LQR approach. The developed PID controller can be applied to a general time‐delayed multivariable analog system represented by a semi‐proper or strictly proper transfer function matrix. Illustrative examples are given to compare the performance of the proposed approach with alternative techniques.     

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.