Radiation damage in flexible TFTs and organic detectors

In this thesis was investigated the radiation hardness of the building blocks of a future flexible X-ray sensor system. The characterized building blocks for the pixel addressing and signal amplification electronics are high mobility semiconducting oxide transistors (HMSO-TFTs) and organic transistors (OTFTs), whereas the photonic detection system is based on organic semiconducting single crystals (OSSCs). TFT parameters such as mobility, threshold voltage and subthreshold slope were measured as function of cumulative X-ray dose. Instead for OSSCs conductivity and X-ray sensitivity were analysed after various radiation steps. The results show that ionizing radiation does not lead to degradation in HMSO-TFTs. Instead OTFTs show instability in mobility which is reduced up to 73% for doses of 1 kGy. OSSC demonstrate stable detector properties for the tested total dose range. As conclusion, HMSO-TFTs and OSSCs can be readily employed in the X-ray detector system allowing operation for total doses exceeding 1 kGy of ionizing radiation

Investigation of Thermal Stress Degradation in Indium-Gallium-Zinc-Oxide TFTs

The performance of IGZO TFTs has improved significantly in recent years, however device stability still remains a significant issue. Thermal stability of IGZO TFTs be- comes very crucial to ensure desired performance of end-product. Both bottom-gate (BG) and double-gate (DG) TFTs were observed to degrade with hotplate treatments under 200◦C. Such events are rarely reported in the literature, and thus became the primary focus of this work. The mechanism causing the instability is not completely understood, however experimental results indicate the instability occurs either di- rectly or indirectly due to the influence of H2O within the passivation oxide above the IGZO channel region. DG TFTs saw more pronounced degradation, which led to the hypothesis that there may be a reaction of the top gate metal with H2O molecules in the passivation oxide, liberating monatomic hydrogen. Both H2O and hydrogen behave as donor states in IGZO, thus rendering the channel more conduc- tive. The thermal stability also demonstrated a dependence on channel length, with shorter channel devices showing greater stability. This may be due to the metalized source/drain regions acting as effective getter to water during a 400◦C passivation anneal which is performed prior to top-gate metal deposition. This hypothesis led to an investigation on atomic layer deposition (ALD) of capping layers over the passiva- tion oxide of IGZO TFTs to act as an effective barrier to water/hydrogen migrating to the underlying IGZO channel

Kelvin force microscopy of polymer and small molecule thin-film transistors

By their nature, scanning probe microscopy (SPM) measurements are ideally suited to the study of organic thin-film transistors (TFTs). In Chapter 3 surface potentialmeasurements are made on TFTs made from the polymer pBTTT. The modification of the surface morphology by annealing into the liquid crystalline phase is examined and the separation between crystalline layers is found to be in agreement with the literature.Kelvin force gradient microscopy (KFGM) measurements provide a very detailed picture of the local potential within the channel of the TFT, allowing for the separation of the device and ?film mobilities in both the linear and saturation regimes. Once the effects of the contacts are removed, the linear mobility is found to be four times higher than the saturation mobility, although the model that best fits the data assumes a constant mobility. Short channel effects are studied in saturation and an upper bound placed on the magnitude of the channel-length modulation. The contactsare also studied in more detail and it is found that a broad region of the pBTTT film near the contacts shows increased resistance, modulated by the gate voltage.In Chapter 4, KFGM is applied to TFTs produces with zone-cast TIPS pentacene as the active material. The seemingly uniform linear crystallites are found to exhibit a wide range of different behaviours, resulting in device characteristics based on statistical averages of many crystallites. The AFM is used to define a single-crystaldevice and this is found to contain two distinct regions of widely divergent mobility. The highest mobility regions imply that the maximum theoretical mobility is muchhigher than is achieved with zone-casting. Greater control over the crystallisation of the film could result in significant increases in device performance. Scanned gate microscopy measurements are also performed and susceptibility to local gating is linked to the conductivity of the film

Indium-Gallium-Zinc Oxide Thin-Film Transistors for Active-Matrix Flat-Panel Displays

Amorphous oxide semiconductors (AOSs) including amorphous InGaZnO (a-IGZO) areexpected to be used as the thin-film semiconducting materials for TFTs in the next-generation ultra-high definition (UHD) active-matrix flat-panel displays (AM-FPDs). a-IGZO TFTs satisfy almost all the requirements for organic light-emitting-diode displays (OLEDs), large and fast liquid crystal displays (LCDs) as well as three-dimensional (3D) displays, which cannot be satisfied using conventional amorphous silicon (a-Si) or polysilicon (poly-Si) TFTs. In particular, a-IGZO TFTs satisfy two significant requirements of the backplane technology: high field-effect mobility and large-area uniformity.In this work, a robust process for fabrication of bottom-gate and top-gate a-IGZO TFTs is presented. An analytical drain current model for a-IGZO TFTs is proposed and its validation is demonstrated through experimental results. The instability mechanisms in a-IGZO TFTs under high current stress is investigated through low-frequency noise measurements. For the first time, the effect of engineered glass surface on the performance and reliability of bottom-gate a-IGZO TFTs is reported. The effect of source and drain metal contacts on electrical properties of a-IGZO TFTs including their effective channel lengths is studied. In particular, a-IGZO TFTs with Molybdenum versus Titanium source and drain electrodes are investigated. Finally, the potential of aluminum substrates for use in flexible display applications is demonstrated by fabrication of high performance a-IGZO TFTs on aluminum substrates and investigation of their stability under high current electrical stress as well as tensile and compressive strain

Development of p-type oxide semiconductors based on tin oxide and its alloys: application to thin film transistors

In spite of the recent p-type oxide TFTs developments based on SnOx and CuxO, the results achieved so far refer to devices processed at high temperatures and are limited by a low hole mobility and a low On-Off ratio and still there is no report on p-type oxide TFTs with performance similar to n-type, especially when comparing their field-effect mobility values, which are at least one order of magnitude higher on n-type oxide TFTs. Achieving high performance p-type oxide TFTs will definitely promote a new era for electronics in rigid and flexible substrates, away from silicon. None of the few reported p-channel oxide TFTs is suitable for practical applications, which demand significant improvements in the device engineering to meet the real-world electronic requirements, where low processing temperatures together with high mobility and high On-Off ratio are required for TFT and CMOS applications. The present thesis focuses on the study and optimization of p-type thin film transistors based on oxide semiconductors deposited by r.f. magnetron sputtering without intentional substrate heating. In this work several p-type oxide semiconductors were studied and optimized based on undoped tin oxide, Cu-doped SnOx and In-doped SnO2. The influence of the deposition parameters, such as the percentage of oxygen and the deposition pressure and post deposition annealing treatments (up to 200 °C) parameters was investigated in order to optimize the properties of the p-type thin films. The detailed study of the material was accomplished through various techniques of characterization of their electrical and optical properties, crystal structure, chemical composition, topology and morphology. The obtained undoped SnOx thin films showed p-type conduction for a narrow percentage of oxygen, between 2.5% and 4%, after an annealing treatment at 150 °C and 200 °C. The thin films have a mixture of both tetragonal β-Sn and α-SnO phases, mobilities between1.6 cm2/Vs and 2.6 cm2/Vs and a carrier concentration between 1016 and 1017 cm-3. TFTs produced with this material were optimized presenting very good electrical performances, with On-Off ratio ~104, µFE up to 3.5cm2/Vs and Vth between -0.41 V and 15 V. The influence of the dielectric was also studied and leading to new results. Depending on the gate dielectric used, n-, p-type and ambipolar devices were obtained for the same semiconductor deposition conditions. Doping SnOx with Cu also results in transparent p-type oxide semiconductors with mobilities between 1.6 cm2/Vs and 2.6 cm2/Vs and a carrier concentration between 1016 and 1017 cm-3. When applied as active layer, resulted in poor performance thin film transistors, with lower On-Off ratio and the higher Vth, despite µFE increased. When doping the SnO2 films with In, p-type conduction was achieved without the need of the annealing treatment. The obtained as deposited thin films are amorphous and show mobilities up to 27 cm2 /Vs and very low resistivities ~10-3 Ω cm, obtaining in this way the a p-type oxide transparent conductor with the lowest electrical resistivity so far reported in the literature

The Characteristics and Reliability of In-Ga-Zn-O Thin-Film Transistors on Glass and Flexible Polyimide Substrate under Temperature and Illumination Stress

학위논문 (박사)-- 서울대학교 대학원 : 전기컴퓨터공학부, 2013. 2. 한민구.Recently, flexible displays have attracted considerable attention in the emerging electronic device market. Flexible plastic substrates have the advantages such as flexibility, ruggedness and light-weight and its low cost, compared to glass substrate. Indium-Gallium-Zinc-Oxide thin-film transistors (IGZO TFTs) are promising candidates for next generation display backplane due to high mobility, good uniformity, and low process temperature, which suitable for flexible display. In this thesis, the characteristics and reliability of flexible IGZO TFTs were presented and discussed. Firstly, the electrical characteristics and reliability of IGZO TFTs on glass substrate are discussed. The IGZO TFTs were fabricated on a glass substrate with an inverted staggered structure. The initial electrical characteristics and gate bias induced instability was investigated. And drain bias induced instability is investigated. Unique degradation phenomenon was observed under the high drain bias stress. After the high drain bias stress, the drain current, measured at the low drain bias, was significantly decreased. Based on the experimental results, I proposed a degradation model for the high drain bias induced degradation. And light-induced hysteresis of IGZO TFTs is investigated. Hysteresis was observed under the 450-nm illumination, and was increased with temperature. And hysteresis was increased with wavelength decrease. Light-induced hysteresis occurs due to increased sub-band gap states at the interface between the gate insulator layer and the active layer. Also, bias illumination stress induced instability is investigated. The transfer curve did not change after positive bias illumination stress. However, the transfer curve shifted to a negative direction after negative bias illumination stress. The transfer curve could be shifted to the negative direction after negative bias illumination stress due to the increase of VO2+ states. Secondly, the electrical characteristics and reliability of IGZO TFTs on flexible substrate are discussed. The IGZO TFTs were fabricated on a polyimide (PI) substrate with an inverted staggered structure. An inorganic buffer layer, composed of SiO2 and SiNx multi-layer, was employed, in order to prevent the environmental stress, such as water or oxygen molecules. The effects of PI and inorganic buffer layer on the characteristics and reliability of IGZO TFTs were investigated. And the effects of passivation layer on the electrical stability of IGZO TFTs with single passivation layer and double passivation layer fabricated on PI substrate were investigated. The positive bias stress and negative bias stress were applied to the IGZO TFTs at various temperatures from 20 oC to 80 oC. The threshold voltage shift of double passivation device was larger than that of single passivation device under NBTS. The threshold voltage shift of double passivation device was slightly less than that of single passivation device under PBTS. The threshold voltage shift of NBTS is considerably increased than that of PBTS at high temperature due to the difference between conduction band offset and valence band offset. Lastly, the effects of mechanical bending on the electrical stability of flexible IGZO TFTs were investigated.Abstract i Contents iv List of Tables vii List of Figures viii Chapter 1 Introduction 1 1.1 Evolution of display technology 2 1.2 Outline of this thesis 10 Chapter 2 Review of IGZO TFTs and flexible display technology 11 2.1 Recent issues of IGZO TFTs 12 2.1.1 Reliability under bias temperature stress 14 2.1.2 Reliability under negative bias illumination stress 18 2.1.3 Reliability under various environments 24 2.2 Various backplane materials for flexible display 30 Chapter 3 The electrical characteristics and reliability of IGZO TFTs on glass substrate 33 3.1 Overview 34 3.2 Fabrication process of IGZO TFTs on glass substrate 36 3.3 Electrical characteristics of IGZO TFTs 39 3.4 Gate bias induced instability without illumination 42 3.5 Drain bias induced instability without illumination 46 3.5.1 Introduction 46 3.5.2 Experimental methods 48 3.5.3 Experimental results and discussions 49 3.5.4 Conclusion 63 3.6 Light-Induced Hysteresis of IGZO TFTs with Various Wavelengths 64 3.6.1 Introduction 64 3.6.2 Experimental methods 65 3.6.3 Experimental results and discussions 66 3.6.4 Conclusion 75 3.7 Light-Induced Hysteresis of IGZO TFTs with Various Temperatures 76 3.7.1 Introduction 76 3.7.2 Experimental methods 78 3.7.3 Experimental results and discussions 79 3.7.4 Conclusion 89 3.8 Bias illumination stress induced instability 90 Chapter 4 The electrical characteristics and reliability of IGZO TFTs on flexible substrate 99 4.1 Overview 100 4.2 Fabrication process of IGZO TFTs on polyimide substrate 102 4.3 Comparison between IGZO TFTs on glass substrate and flexible substrate 105 4.4 Effects of the buffer layer on the electrical characteristics of flexible IGZO TFTs 109 4.5 Effects of passivation layer on the electrical stability of flexible IGZO TFTs 115 4.5.1 Introduction 115 4.5.2 Experimental methods 117 4.5.3 Experimental results and discussions 119 4.5.4 Conclusion 127 4.6 Effects of humidity on the electrical characteristics of IGZO TFTs 128 4.7 Effects of mechanical bending on the electrical stability of flexible IGZO TFTs 139 Chapter 5 Summary 154 Bibliography 156 초 록 175Docto

Light-induced effects on oxide based thin film transistors

Dissertação de Mestrado, Engenharia Eletrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2016Este trabalho incidiu sobre a análise elétrica dos transístores com base em óxidos semicondutores. Esta é uma área emergente e tecnologicamente relevante. Numa primeira fase a dissertação aborda com detalhe, os aspetos essenciais dos transístores com base em óxido semiconductor: Discute-se a sua origem, estrutura, os métodos de fabrico e as aplicações. Depois desta introdução, os efeitos da exposição à luz nas propriedades elétricas dos transístores são apresentados e discutidos em detalhe. Foram estudados transístores preparados através de uma solução líquida de ureia. Este processo de fabrico torna possível imprimir ou depositar o semicondutor em substratos flexíveis e de baixo custo, abrindo um conjunto de novas oportunidades para tecnologia eletrónica com base em óxidos amorfos semicondutores. Até recentemente esta possibilidade de imprimir eletrónica era apenas possível com transístores orgânicos. Os problemas relacionados com a exposição de luz em transístores de óxidos amorfos tem sido estudados na literatura e atribuídos a interação de cargas elétricas com defeitos no semiconductor. Este tipo de defeito é conhecido por lacunas de oxigénio. Estes defeitos eletrónicos foto-induzidos afetam a performance do transístor e modificam temporariamente os seus parâmetros, nomeadamente a mobilidade de efeito de campo, a tensão de arranque, a condutividade elétrica, as correntes de fuga e a estabilidade operacional. Os resultados obtidos nesta dissertação mostram que a exposição prolongada à luz com energia igual ou superior ao hiato do ZTO induzem estados dopantes duradouros. Estes estados dopantes estão localizados aproximadamente a 0.14 eV do limite da banda de condução. É proposto que as espécies químicas responsáveis pelos estados induzidos pela luz, sejam os espaços não ocupados do oxigénio ionizado. Porém, mais experiências são precisas para provar esta proposta. A iluminação afeta também a estabilidade operacional do transístor. Transístores submetidos à iluminação sofre de uma rápida variação da tensão de arranque. Transístores fabricados usando ureia são mais instáveis do que que transístores fabricados usando técnicas de sublimação térmica. Estas diferenças de comportamento são atribuídas à presença de defeitos eletricamente ativos. Sugere-se que estes defeitos estão localizados na interface entre o dielétrico e semicondutor. Estudos da corrente que flui no transístor em função da temperatura revelam um comportamento anómalo. Foram detetadas dois tipos de anomalias uma devido aos estado induzidos pela luz e outra causada pela presença de uma quantidade residual de água na superfície do dielétrico

Characterization and Fabrication of Active Matrix Thin Film Transistors for an Addressable Microfluidic Electrowetting Channel Device

The characterization and fabrication of active matrix thin film transistors (TFTs) has been studied for an addressable microfluidic electrowetting channel device as application. A new transparent semiconductor material, Amorphous Indium Gallium Zinc Oxide (a-IGZO), is used for TFT, which shows high electrical performance rather than amorphous silicon based TFT; higher mobility and even higher transparency. The purpose of this dissertation is to optimize each TFT process including the optimization of a-IGZO properties to achieve robust device for application. To minimize hysteresis of TFT curves, the gate dielectric is discussed extensively in this dissertation. By optimizing gas ratio of NH3SiH4, it is found that the TFT with NH3 rich SiNx gate dielectric deposited with NH3/SiH4 =5.1 and stoichiometric SiO2 demonstrates best condition to reduce hysteresis. a-IGZO films is investigated as a function of power and substrate bias effect which affects to electrical performance; the higher power and substrate bias increase the carrier density in the film and mainly cause threshold voltage(VT) to shift in the negative gate voltage direction and mobility to increase, respectively. In addition, the powerful method to estimate the electrical properties of a-IGZO is proposed by calculating O2 and IGZO flux during sputtering in which the incorporation ratio with O2/IGZO ≈1 demonstrates the optimized a-IGZO film for TFT. It is confirmed that both physical and chemical adsorption affects the electrical property of a-IGZO channel by studying TFT-IV characteristics with different pressure and analyzing X-ray photoelectron spectroscopy (XPS), which mainly affects the VT instability. The sputtered SiO2 passivation shows better electrical performance. To achieve electrically compatible (lower back channel current) a-IGZO film to SiO2 sputter passivated device, a-IGZO TFTs require oxygen rich a-IGZO back channel by employing two step a-IGZO deposition process (2nd 10nm a-IGZO with PO2 = 1.5mTorr on 1st 40nm a-IGZO with PO2=1mTor). Electrowetting microfluidic channel device as application using a-IGZO TFTs is studied by doing preliminary test. The electrowetting channel test using polymer post device platform is candidate for addressable electrowetting microfluidic channel device driven by active matrix type a-IGZO TFT

O2 플라즈마, 자외선 조사, Biased-H2O 어닐링을 통한 저온 용액공정을 이용한 산화물 박막트랜지스터의 특성 향상에 대한 연구

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2013. 8. 한민구.Zinc tin oxide (ZTO)나 indium gallium zinc oxide (IGZO)를 이용한 용액공정형 산화물 박막 트랜지스터는 고이동도, 빛 투명성, 플렉서블 적합성, 물질의 광범위함, 분자 구성비에 의한 전기적 특성 조절 용이성 등의 장점 때문에 실리콘 기반의 박막 트랜지스터와 유기물 박막 트랜지스터를 대체하며 능동 매트릭스형 디스플레이의 구동 소자로서 상당한 주목을 받고 있다. 용액공정형 산화물 박막 트랜지스터는 능동 매트릭스형 액정표시장치와 능동 매트릭스형 유기발광다이오드 디스플레이 백플레인으로서 많은 문제점을 가지고 있는 실리콘 기반의 박막 트랜지스터와 유기물 박막 트랜지스터와 비교하여 우수한 특성을 보여주고 있다. 더욱이, 용액공정형 산화물 박막 트랜지스터는 우수한 균일성과 고처리량 덕분에 대면적 공정에 적합하다. ZnO 기반의 산화물 반도체 중에서, Sn 물질을 이용한 ZTO 박막 트랜지스터는 Sn이 널리 사용되고 있는 In 보다 상당히 저가의 물질이기 때문에 저가 공정을 확립하는데 유망한 소자이다. 추가적인 가격 절감과 플렉서블 디스플레이로의 응용성 확장을 위해서 용액공정형 ZTO 박막 트랜지스터는 저렴하고 플렉서블한 기판에 제작되어야 한다. 플렉서블한 기판은 고온에서 쉽게 손상되기 때문에 플렉서블한 기판에 용액공정형 ZTO 박막 트랜지스터가 제작되기 위해서는 저온 공정이 요구된다. 그러나, 저온에서 제작된 용액공정형 ZTO 박막 트랜지스터는 낮은 on-currnet, 높은 문턱 접압, 낮은 이동도 등의 열등한 특성을 가지므로, 우수한 특성의 용액공정형 ZTO 박막 트랜지스터를 제작하기 위해서는 500도 이상의 고온 공정이 필요하다. 저온에서 제작된 용액공정형 산화물 박막 트랜지스터의 소자 특성을 향상시키기 위해서는, 용액공정형 산화물 박막 트랜지스터에 대한 어닐링 온도의 영향성과 더불어 저온 공정에서 제작되더라도 우수한 소자 특성을 가지도록 하는 연구가 요구된다. 기존에 용액공정형 산화물 박막 트랜지스터에 대한 어닐링 온도의 영향상을 분석하려는 시도가 있었지만, 용액공정형 산화물 박막 트랜지스터에 대한 어닐링 온도 영향성의 전기적, 화학적 메커니즘은 거의 연구되지 않았다. 이 논문의 목적은 용액공정을 이용하여 다양한 어닐링 온도에서 산화물 박막 트랜지스터를 제작하여 문턱 전압, 포화 이동도, 신뢰성 등의 용액공정형 산화물 박막 트랜지스터의 전기적 특성에 대한 어닐링 온도의 영향성을 분석하고, 제안된 O2 플라즈마, 자외선 조사, Biased-H2O 어닐링 등의 방법을 통하여 능동 매트릭스형 디스플레이를 위한 저온 용액공정 산화물 박막 트랜지스터의 전기적 특성을 향상시키는 것이다.Solution-processed oxide thin film transistors (TFTs) with zinc-tin-oxide (ZTO) and indium-gallium-zinc-oxide (IGZO) have attracted considerable attention for the driving elements of active matrix display, instead of Si-based TFTs and organic TFTs, because of high mobility, visible light transparency, flexibility, wide range of materials, and controllability of electrical properties by atomic composition. Solution-processed oxide TFTs show superior performance for active matrix liquid crystal display (AMLCD) and active matrix organic light emitting diode (AMOLED) display backplanes, compared with solution-processed Si and organic TFTs which have a number of issues. Furthermore, solution-processed oxide TFTs are compatible with large area due to good uniformity and high throughput, so that could be a method for achieving low cost fabrication contrary to vacuum processes. Among various ZnO-based oxide semiconductors, ZTO TFTs employing tin (Sn) material maybe promising candidates for achieving low cost processes because Sn is a quite low cost material compared with widely used indium (In). Solution-processed ZTO TFTs need to be fabricated on inexpensive and flexible substrates such as glass and plastic for additional cost reduction and application extension to a flexible display. For solution-processed ZTO TFTs fabrication with these flexible substrates, low temperature processes are necessary because these substrates are easily damaged at high annealing temperatures. At low annealing temperature, however, solution-processed ZTO TFTs have poor performance such as low on-current, high threshold voltage and low mobility, so a rather high annealing temperature exceeding 500 °C is required in solution-processed ZTO TFTs. To improve the device characteristics of solution-processed oxide TFTs even at low annealing temperature on an active layer, a study of the effects of annealing temperature on the electrical characteristics of solution-processed oxide TFTs and the efforts to achieve high device characteristics of solution-processed oxide TFTs even at low annealing temperature on active layer are desired. There were some efforts to investigate the effects of annealing temperature on solution-processed oxide TFTs, but the electrical and chemical mechanisms of annealing temperature on solution-processed oxide TFTs have been scarcely studied. The purpose of this thesis is to fabricate oxide TFTs employing solution-process for an oxide semiconductor active layer with various annealing temperatures to investigate the effects of annealing temperature on the electrical characteristics of solution-processed oxide TFTs such as threshold voltage, saturation mobility, and reliability, and to improve the electrical characteristics of low temperature solution-processed oxide TFTs for low cost, stable, and flexible active matrix display backplane. The effects of annealing temperature on the bonding structure of ZTO active layer in solution-processed ZTO TFTs were investigated and the chemical formation equation of the ZTO active layer with regard to the annealing temperature was established. To improve the electrical characteristics of low temperature solution-processed oxide TFTs according to the investigation of effects of annealing temperature in regard of the chemical formation of ZTO active layer, O2 plasma treatment, UV radiation treatment, and the biased-H2O annealing were proposed to achieve high device characteristics of solution-processed oxide TFTs even at low annealing temperature. Moreover, the effects on electrical and chemical characteristics of solution-processed oxide TFTs with proposed methods were investigated in detail. These proposed methods to improve the electrical characteristics of low temperature solution-processed oxide TFTs would be suitable for the low cost, stable, and flexible active matrix display backplane.Abstract i Contents iv List of Tables vii List of Figures ix Chapter 1 Introduction 1 1.1 Recent flat panel display technology 2 1.2 Device parameter extraction 12 1.3 Dissertation organization 14 Chapter 2 Review of solution-processed oxide TFTs 16 2.1 Overview of oxide TFTs 17 2.2 Advantages of solution-process 25 2.3 Solution-processed oxide TFTs 30 Chapter 3 Optimization of the fabrication process of solution-processed oxide TFTs 36 3.1 Overview 37 3.2 Structure of solution-processed oxide TFTs 38 3.3 Stirring time on solution-processed oxide TFTs 47 3.4 Active layer thickness on solution-processed oxide TFTs 56 3.5 Effects of passivation on solution-processed oxide TFTs 60 3.6 Electrical characteristics of solution-processed oxide TFTs 63 3.6.1 Transfer characteristics 63 3.6.2 Reliability characteristics 68 Chapter 4 Effects of Annealing Temperature on Solution-processed oxide TFTs 75 4.1 Motivation 76 4.2 Fabrication of solution-processed ZTO TFTs with various annealing temperature 78 4.3 Electrical characteristics with the increase in annealing temperature 80 4.4 Dechlorination on threshold voltage with the increase in annealing temperature 83 4.5 Dechlorination and crystallization on saturation mobility with the increase in annealing temperature 89 4.6 Reliability characteristics with the increase in annealing temperature 93 4.7 Chemical formation equations with the increase in annealing temperature 95 4.8 Conclusion 99 Chapter 5 Improvement of low temperature solution-processed oxide TFTs 100 5.1 Improvement of low temperature solution-processed oxide TFTs employing O2 plasma treatment 101 5.1.1 Motivation 101 5.1.2 Fabrication of solution-processed ZTO TFTs employing O2 plasma treatment 104 5.1.3 Electrical characteristics with O2 plasma treatment 108 5.1.4 Preferential dissociation of Cl on threshold voltage by O2 plasma treatment 111 5.1.5 Increase of electron concentration on saturation mobility by O2 plasma treatment 116 5.1.6 Reliability characteristics with O2 plasma treatment 119 5.1.7 Conclusion 122 5.2 Improvement of low temperature solution-processed oxide TFTs employing Ultra-Violet radiation treatment 123 5.2.1 Motivation 123 5.2.2 Fabrication of solution-processed ZTO TFTs employing UV radiation treatment 126 5.2.3 Electrical characteristics with UV radiation treatment 130 5.2.4 Effects of UV radiation treatment on oxide active layer semiconductors 133 5.2.5 Generation of hydroxide(-OH) bonding by UV radiation treatment on oxide active layer semiconductors 137 5.2.6 Conclusion 141 5.3 Improvement of low temperature solution-processed oxide TFTs employing biaed-H2O annealing 142 5.3.1 Motivation 142 5.3.2 Effects of various annealing condition 145 5.3.3 Effects of H2O wet annealing according to the annealing temperature 148 5.3.4 Proposed biased-H2O annealing to improve low temperature solution-processed oxide TFTs 154 5.3.5 Conclusion 161 Chapter 6 Summary 162 Bibliography 171 초 록 191Docto

Metal oxide semiconductor thin-film transistors for flexible electronics

The field of flexible electronics has rapidly expanded over the last decades, pioneering novel applications, such as wearable and textile integrated devices, seamless and embedded patch-like systems, soft electronic skins, as well as imperceptible and transient implants. The possibility to revolutionize our daily life with such disruptive appliances has fueled the quest for electronic devices which yield good electrical and mechanical performance and are at the same time light-weight, transparent, conformable, stretchable, and even biodegradable. Flexible metal oxide semiconductor thin-film transistors (TFTs) can fulfill all these requirements and are therefore considered the most promising technology for tomorrow's electronics. This review reflects the establishment of flexible metal oxide semiconductor TFTs, from the development of single devices, large-area circuits, up to entirely integrated systems. First, an introduction on metal oxide semiconductor TFTs is given, where the history of the field is revisited, the TFT configurations and operating principles are presented, and the main issues and technological challenges faced in the area are analyzed. Then, the recent advances achieved for flexible n-type metal oxide semiconductor TFTs manufactured by physical vapor deposition methods and solution-processing techniques are summarized. In particular, the ability of flexible metal oxide semiconductor TFTs to combine low temperature fabrication, high carrier mobility, large frequency operation, extreme mechanical bendability, together with transparency, conformability, stretchability, and water dissolubility is shown. Afterward, a detailed analysis of the most promising metal oxide semiconducting materials developed to realize the state-of-the-art flexible p-type TFTs is given. Next, the recent progresses obtained for flexible metal oxide semiconductor-based electronic circuits, realized with both unipolar and complementary technology, are reported. In particular, the realization of large-area digital circuitry like flexible near field communication tags and analog integrated circuits such as bendable operational amplifiers is presented. The last topic of this review is devoted for emerging flexible electronic systems, from foldable displays, power transmission elements to integrated systems for large-area sensing and data storage and transmission. Finally, the conclusions are drawn and an outlook over the field with a prediction for the future is provided