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Fabrication and Characterization of Amorphous InGaZnO Thin Film Transistor for Flexible Devices

Fabrication and Characterization of Amorphous InGaZnO Thin Film Transistor for Flexible Devices
Translated Title
유연소자 응용을 위한 비정질 InGaZnO 박막트랜지스터의 공정 및 전기적 특성분석
Lee, Gwangjun
Jang, Jae Eun
Choi, Hong Soo
Issue Date
Available Date
Degree Date
2018. 2
Oxide TFTFlexible DeviceFlexible ElectrodesFlexible CircuitsFlexible sensorsa-IGZO 박막트랜지스터유연성 전자소자홀구조플렉서블 디바이스
The current interest in transparent amorphous oxide semiconductor (AOS) thin film transistors was performed in operation of amorphous indium gallium-zinc oxide, a-IGZO, TFTs on flexible, room temperature and polymer substrate. AOS area has rapidly devel-oped, with a-IGZO TFT addressed active matrix displays. AOS are a new area of materials with electrical and optical characteristics uniquely suited to transparent, flexible and large area electronics. The a-IGZO TFTs have considerable attracted interest due to a room tem-perature processing, a visible transparency and a large area uniformity. These are ideal prop-erties for using them as active layers in TFTs which form the backbone of active matrix dis-play and large area electronic applications. Nevertheless, for these devices to be commercial-ly viable for flexible electronics, new device design concepts with an electrically analysis of device operation and reliability should be considered. In this dissertation, a-IGZO TFTs on various substrates were studied in the respect of material characteristics, the design of de-vice and its electrical performances. One of the key features of a-IGZO TFTs have a much higher field-effect mobility (μFE = >10 cm2/V·s) compared to a-Si:H TFTs, a low threshold voltage exhibiting in en-hancement mode operation, excellent switching properties, and a small parasitic series re-sistance employing IZO as source/drain electrode without the additional contact doping process. Process optimization of a-IGZO TFT was performed in scaling channel length, temperature-dependence and oxygen dispersion on active surface. A bendable a-IGZO TFTs and inverter circuits was demonstrated on a thin glass sub-strate. From the bending tests on the TFTs, VTH was negatively shifted as an increase of the bending strain for the symmetric gate overlap sample, while the TFTs showed relatively sta-ble operation against mechanical strain for the asymmetric gate overlap sample. Owing to the high temperature thermal annealing process, the a-IGZO TFTs showed very good bias stress stability under prolonged positive and negative stress test. Therefore, transparent, flexible, and stable TFTs can be realized using the a-IGZO TFTs on the thin glass substrate which can open a new topic for flexible display applications. Finally, we demonstrated high performance and flexible a-IGZO TFTs with hole-array on polyimide substrate and investigated the variation in the electrical characteristics as a function of hole area and radius. The a-IGZO TFTs with hole-array device performance shows good electrical characteristics and the mechanical strain reduced remarkably in hole-array structure as compared with the TFT without hole-array. Electrical stability measure-ments of the flexible devices with hole-array structure under tensile and compressive me-chanical strain showed no appreciable change in the I-V characteristics during bending. The electrical characteristics under mechanical bending suggest that carrier transport was unaf-fected during mechanical strain. Testing under dc gate bias conditions, the electrical stabil-ity of the TFTs showed a positive VTH shift of 3.8 V after 3600 s without any change in subthreshold-swing (S.S.). The a-IGZO TFTs with hole array structure exhibits high on/off ratio of >106 and field effect mobility of >6 cm2/V·s even after high bending radius. The bending radius was set to 100 mm by considering minimum bending radius (tensile strain of 0.22 % perpendicular to the channel current flow). The a-IGZO TFTs with hole-array re-markably reduced more electrical failure than TFT without hole-array samples since discon-nected micro-cracks induced the release of mechanical strain. Thus, proposed hole-array structure of a-IGZO TFTs can give an important merit to use flexible devices. ⓒ 2017 DGIST
Table Of Contents
I. INTRODUCTION 1-- 1.1 Background and Motivation 1-- 1.2 Flexible Electronics 6-- 1.3 Organization of Dissertation 9-- II. PROCESS OPTIMIZATION AND ELECTRICAL CHARACTERIZATION OF a-InGaZnO THIN FILM TRANSISTOR 11-- 2.1 Introduction 11-- 2.2 Scaling channel length effect of a-IGZO TFTs with a-IZO electrodes 12-- 2.3 Temperature effect of a-IGZO TFTs 25-- 2.3.1 Temperature-dependent current-voltage characteristics 26-- 2.3.2 Temperature-dependent parameter extraction 29-- 2.4 Oxygen dispersive diffusion effect of a-IGZO TFTs 34-- III. BENDING EFFECT OF a-InGaZnO THIN FILM TRANSISTOR AND BIAS STRESS IN-STABILITY TEST 3.1 Introduction 45-- 3.2 a-IGZO TFT on thin glass substrate 47-- 3.3 Characteristics of symmetry and asymmetry in a-IGZO active 50-- 3.4 Bending effect of a-IGZO active 52-- 3.5 Depletion and enhancement load type inverter 53-- 3.6 Prolonged positive and negative gate bias stress tests 55-- IV. STRUCTURAL EFFECT OF HOLE WITH ELECTRODE AND a-InGaZnO THIN FILM TRANSISTOR 4.1 Introduction 59-- 4.2 Device Structure and Fabrication 60-- 4.3 The Hole Drilling Method 61-- 4.4 Various hole-array structure 63-- 4.5 Hole-array effect with a-IGZO active 67-- V. CONCLUSION 72-- References 75
Information and Communication Engineering
Related Researcher
  • Author Jang, Jae Eun Advanced Electronic Devices Research Group(AEDRG)
  • Research Interests Nanoelectroinc device; 생체 신호 센싱 시스템 및 생체 모방 디바이스; 나노 통신 디바이스
Department of Information and Communication EngineeringThesesPh.D.

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