An amorphous oxide semiconductor thin-film transistor route to oxide electronics

Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) invented only one decade ago are now being commercialized for active-matrix liquid crystal display (AMLCD) backplane applications. They also appear to be well positioned for other flat-panel display applications such as active-matrix organic light-emitting diode (AMOLED) applications, electrophoretic displays, and transparent displays. The objectives of this contribution are to overview AOS materials design; assess indium gallium zinc oxide (IGZO) TFTs for AMLCD and AMOLED applications; identify several technical topics meriting future scrutiny before they can be confidently relied upon as providing a solid scientific foundation for underpinning AOS TFT technology; and briefly speculate on the future of AOS TFTs for display and non-display applications

Amorphous In-Ga-Zn-O Thin-Film Transistors for Next Generation Ultra-High Definition Active-Matrix Liquid Crystal Displays.

Next generation ultra-high definition (UHD) active-matrix flat-panel displays have resolutions of 3840x2160 (4K) or 7680x4320 (8K) pixels shown at 120 Hz. The UHD display is expected to bring about immersive viewing experiences and perceived realness. The amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) is a prime candidate to be the backplane technology for UHD active-matrix liquid crystal displays (AM-LCDs) because it simultaneously fulfills two critical requirements: (i) sufficiently high field-effect mobility and (ii) uniform deposition in the amorphous phase over a large area. We have developed a robust a-IGZO density of states (DOS) model based on a combination of experimental results and information available in the literature. The impact of oxygen partial pressure during a-IGZO deposition on TFT electrical properties/instability is studied. Photoluminescence (PL) spectra are measured for a IGZO thin films of different processing conditions to identify the most likely electron-hole recombination. For the first time, we report the PL spectra measured within the a IGZO TFT channel region, and differences before/after bias-temperature stress (BTS) are compared. To evaluate the reliability of a-IGZO TFTs for UHD AM-LCD backplane, we have studied its ac BTS instability using a comprehensive set of conditions including unipolar/bipolar pulses, frequency, duty cycle, and drain biases. The TFT dynamic response, including charging characteristics and feedthrough voltage, are studied within the context of 4K and 8K UHD AM-LCD and are compared with hydrogenated amorphous silicon technology. We show that the a-IGZO TFT is fully capable of supporting 8K UHD at 480 Hz. In addition, it is feasible to reduce a-IGZO TFT feedthrough voltage by controlling for non-abrupt TFT switch-off.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111526/1/ekyu_1.pd

Stacks of alternating conductive and non-conductive oxides for controlling electric fields at a spatial resolution of 100 nm in the core of a waveguide

Holography is a revolutionary display technology capable of creating a true three-dimensional 3D image. In Hollywood movies such as "Star Wars", advanced holograms at video-rate are often present and appreciated by the audience. Unfortunately, despite many efforts from the scientific community, fast rewritable high-quality holograms haven't been created yet. This work focuses on developing a structure capable of bringing this type of holography to life. To achieve this, a slab waveguide is proposed, where the core contains an electro-refractive material. By applying local electric fields with analog control and nano-precision inside the core, its refractive index will change locally. Light traveling along the core, when encountering the affected area, will be leaked into free space and create a hologram. These electric fields will be controlled through one of the conductive pillars of the cladding structure. For the latter, a novel metamaterial is being developed and this work centres on its optimization. For this, transparent conductive oxides (TCO) will be used, as metals will lead to parasitic scattering and absorption of light in the cladding. Hence, the optical properties of the alternating conductive and non-conductive oxide pillars of Indium Gallium Zinc Oxide (IGZO) and Silicon-Oxy Nitride (SiOxNy), respectively, need to be matched. In this study, the refractive index and extinction coefficient of both materials have been determined by spectroscopy ellipsometry (SE) and compared. IGZO pillars were created by optical photolithography and the appropriate etch time was optimized. Finite-difference time-domain (FDTD) simulations were carried out to be compared with future practical results of the structure altogether

전류 센싱 피드백 시스템을 이용한 고안정성 산화물 TFT 쉬프트 레지스터의 설계 및 제작

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2017. 2. 정덕균.Integration of shift registers on the glass panel allows the display to be thinner, lighter, and cheaper to produce, thanks to the reduction of the number of ICs for scanning horizontal lines. Circuits of the shift register employing n-type thin film transistors (TFTs), such as hydrogenated amorphous silicon (a-Si:H) and oxide TFTs, have been reported. Recently, oxide TFTs attract much attention due to their high mobility (5~10 cm2/V∙s) compared with that of a-Si:H TFT (0.8cm2/V∙s). However, oxide TFTs often suffer from severe degradation of the threshold voltage (VTH) against the temperature and electrical stress. In this paper, in order to compensate the instability of oxide TFTs in the shift register, an oxide TFT with double gates, which can control VTH by varying the top gate bias (VTG) is adopted. The top gate of the double-gate TFT can be fabricated in the same process for the pixel IZO (Indium Zinc Oxide) so that an additional process only for the top gate is not required. Adequate VTG is provided timely, adaptively to the gate of the oxide TFTs to stabilize the threshold voltage. The fabrication result shows that the proposed shift register using VTG set at an adapted value become stable at 100℃ whereas the conventional one is mal-functioning. The optimum VTG varies from product to product and changes continuously over the lifetime of the display. Therefore, the feedback driving system suitable for the proposed shift register is required to search the optimum VTG. The system has two main functionsthe first is to sense the current of shift register and the second is the searching algorithm for finding the optimum VTG. When the transistors are degraded by an external stress, the current of the whole shift registers is changed. The information about the VTH degradation in the shift register can be gathered via current sensing circuit. The sensed current is integrated to generate the output and is forwarded to an ADC. The binary-converted current of shift register is processed by the proposed algorithm in the digital domain for obtaining an optimum VTG and then the result is converted back to analog to generate VTG. The IC implementing such functions is fabricated in a 0.18 μm BCDMOS process. When the shift register current is measured on the conventional system with increasing temperature up to 80℃, it is increased to more than 10 times than that at the room temperature. However, the proposed feedback system keeps a highly stable (<13%) current level of shift register up to 80℃ with an optimized VTG.Abstracts i Table of Contents iii List of Tables v List of Figures vi Chapter 1 Introduction 1 1.1 Background 2 1.2 Outline 7 Chapter 2 Review of oxide-based TFT device and N-type TFT circuit design 8 2.1 Overview 9 2.1.1 Characteristics of Oxide TFT 9 2.2 Oxide-based TFT 14 2.2.1 Electrical characteristics of oxide-based TFT 14 2.2.2 Stability of oxide-based TFT 18 2.3 NMOS driving circuit 24 2.3.1 Bootstrapping driving circuit 24 2.3.2 Shift register with n-type TFT 28 Chapter 3 Proposed Oxide TFT Shift Register 37 3.1 Overview 38 3.2 Characteristic of Double Gate TFT 39 3.3 Design of New shift register 46 3.3.1 Simulation Result of Conventional shift register 46 3.3.2 New shift register using Double Gate TFT 51 3.3.3 Simulation Modeling of Double Gate TFT 58 3.3.4 Simulation and Experimental Result 61 Chapter 4 Real Time Current-Sensing Feedback Compensation System 71 4.1 Overview 72 4.2 System Architecture 74 4.3 Circuit Design 77 4.3.1 Current Sensing Block 77 4.3.2 ADC/DAC Block 85 4.4 Optimum Point Searching Algorithm 100 4.5 System Verification 106 Chapter 5 Summary 116 Appendix A SPICE models 118 Bibliography 120Docto

Resistive switching RAM devices based on amorphous oxide semiconductors for system on panel applications

This work reports the mask design, fabrication and characterization of memristor devices with diode like electrical behavior at pristine state. It is due to the presence of Schottky junctions between Zinc-tin-oxide (ZTO) and platinum - Indium-galliumzinc- oxide (IGZO) and molybdenum oxide for two different Metal-Insulator-Metal (MIM) configurations. The devices were exclusively produced using physical vapor deposition processes without intentional heating. Typical advanced electrical analysis of ReRAM device was performed. The Pt-ZTO-TiAu devices showed pinched hysteresis properties with large Ron=of f ratio, fast switching which can be controlled in a digital SET and analog RESET operation. However, large device-to-device variations and stability are the main issues which is due to the processing. On the other hand, the Mo-IGZO-Mo devices showed a small Ron=of f ratio and only analog operation. There was a high yield and stability. However, using DC sweep for cycling led to a charging phenomenon. Using SET/RESET pulses, the devices sustain hundreds of cycles without deterioration or movement of the resistance states, showing great resilience and retention

Backplane Circuit Design with Amorphous Silicon Thin-Film Transistors for Flexible Displays

In recent years, rapid advancement in LED fabrication has enabled the possibility of using GaN micro-LEDs to be the light media in a display panel. It has superior performance in many aspects when compared with OLED technology, such as high contrast, wide viewing angle, and low power consumption. These advantages have enabled a possibility of using micro-LED technology to realize flexible displays. Currently, OLEDs need high mobility low-temperature-poly-silicon (LTPS) TFTs to be the backplane driving circuit material because lower mobility TFTs are inadequate to drive OLEDs. However, LTPS TFTs have poor uniformity over a large area due to unpredictable grain sizes and require additional fabrication processes which prevent it from being integrated onto a large-area flexible platform. On the other hand, conventional amorphous silicon (a-Si:H) technology used on LCD panels have an edge in terms of uniformity over large-area and low-cost fabrication. Even though the field-effect mobility of a-Si:H TFTs is much less than LTPS technology, it is sufficient to power up micro-LEDs with decent pixel density, which is impossible with OLEDs. However, the nature of amorphous materials gives rise to electrical instability issues. The output current of a-Si:H TFTs gradually decreases over time under electrical stress, which results in dimmer micro-LEDs in pixels. Moreover, the lack of complementary p-type TFTs in a-Si:H limits the integration of driver and control circuits onto the flexible platform to realize a full "system-on-flex". To overcome such shortcomings of a-Si:H technologies, this thesis makes a contribution in providing a solution to compensate the output current degradation by a novel pixel circuit with simple control scheme, as well as bootstrapped logic circuits that can be used as row driver and control circuits on flexible substrates. The proposed compensation pixel and row driver circuits can be combined to facilitate the realization of a "system-on-flex" backplane for a display panel with a-Si:H and micro-LED technologies

Wide Bandwidth - High Accuracy Control Loops in the presence of Slow Varying Signals and Applications in Active Matrix Organic Light Emitting Displays and Sensor Arrays

This dissertation deals with the problems of modern active matrix organic light-emitting diode AMOLED display back-plane drivers and sensor arrays. The research described here, aims to classify recently utilized compensation techniques into distinct groups and further pinpoint their advantages and shortcomings. Additionally, a way of describing the loops as mathematical constructs is utilized to derive new circuits from the analog design perspective. A novel principle on display driving is derived by observing those mathematical control loop models and it is analyzed and evaluated as a novel way of pixel driving. Specifically, a new feedback current programming architecture and method is described and validated through experiments, which is compatible with AMOLED displays having the two transistor one capacitor (2T1C) pixel structure. The new pixel programming approach is compatible with all TFT technologies and can compensate for non-uniformities in both threshold voltage and carrier mobility of the pixel OLED drive TFT. Data gathered show that a pixel drive current of 20 nA can be programmed in less than 10usec. This new approach can be implemented within an AMOLED external or integrated display data driver. The method to achieve robustness in the operation of the loop is also presented here, observed through a series of measurements. All the peripheral blocks implementing the design are presented and analyzed through simulations and verified experimentally. Sources of noise are identified and eliminated, while new techniques for better isolation from digital noise are described and tested on a newly fabricated driver. Multiple versions of the new proposed circuit are outlined, simulated, fabricated and measured to evaluate their performance.A novel active matrix array approach suitable for a compact multi-channel gas sensor platform is also described. The proposed active matrix sensor array utilizes an array of P-i-N diodes each connected in series with an Inter-Digitated Electrode (IDE). The functionality of 8x8 and 16x16 sensor arrays measured through external current feedback loops is also presented for the 8x8 arrays and the detection of ammonia (NH3) and chlorine (Cl2) vapor sources is demonstrated

Eurodisplay 2019

The collection includes abstracts of reports selected by the program by the conference committee

Review of Display Technologies Focusing on Power Consumption

Producción CientíficaThis paper provides an overview of the main manufacturing technologies of displays, focusing on those with low and ultra-low levels of power consumption, which make them suitable for current societal needs. Considering the typified value obtained from the manufacturer’s specifications, four technologies—Liquid Crystal Displays, electronic paper, Organic Light-Emitting Display and Electroluminescent Displays—were selected in a first iteration. For each of them, several features, including size and brightness, were assessed in order to ascertain possible proportional relationships with the rate of consumption. To normalize the comparison between different display types, relative units such as the surface power density and the display frontal intensity efficiency were proposed. Organic light-emitting display had the best results in terms of power density for small display sizes. For larger sizes, it performs less satisfactorily than Liquid Crystal Displays in terms of energy efficiency.Junta de Castilla y León (Programa de apoyo a proyectos de investigación-Ref. VA036U14)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA013A12-2)Ministerio de Economía, Industria y Competitividad (Grant DPI2014-56500-R