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| Release | : 2014 |
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| Author | : Fábio Fedrizzi Vidor |
| Publisher | : Springer |
| Total Pages | : 191 |
| Release | : 2017-12-28 |
| Genre | : Technology & Engineering |
| ISBN | : 3319725564 |
This book describes the integration, characterization and analysis of cost-efficient thin-film transistors (TFTs), applying zinc oxide as active semiconductors. The authors discuss soluble gate dielectrics, ZnO precursors, and dispersions containing nanostructures of the material, while different transistor configurations are analyzed with respect to their integration, compatibility, and device performance. Additionally, simple circuits (inverters and ring oscillators) and a complementary design employing (in)organic semiconducting materials are presented and discussed. Readers will benefit from concise information on cost-efficient materials and processes, applied in flexible and transparent electronic technology, such as the use of solution-based materials and dispersion containing nanostructures, as well as discussion of the physical fundamentals responsible for the operation of the thin-film transistors and the non-idealities of the device.
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| Release | : 2016 |
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Abstract : High-performance thin-film transistors (TFTs) with a low thermal budget are highly desired for flexible electronic applications. In this work, the TFTs with atomic layer deposited ZnO-channel/Al2 O3 -dielectric are fabricated under the maximum process temperature of 200°C. First, we investigate the effect of post-annealing environment such as N2, H2 -N2 (4%) and O2 on the device performance, revealing that O2 annealing can greatly enhance the device performance. Further, we compare the influences of annealing temperature and time on the device performance. It is found that long annealing at 200°C is equivalent to and even outperforms short annealing at 300°C. Excellent electrical characteristics of the TFTs are demonstrated after O2 annealing at 200°C for 35 min, including a low off-current of 2.3 × 10 −13 A, a small sub-threshold swing of 245 mV/dec, a large on/off current ratio of 7.6×10 8, and a high electron effective mobility of 22.1 cm 2 /V·s. Under negative gate bias stress at − 10 V, the above devices show better electrical stabilities than those post-annealed at 300°C. Thus the fabricated high-performance ZnO TFT with a low thermal budget is very promising for flexible electronic applications.
| Author | : Yiyang Gong |
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| Release | : 2017 |
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Novel materials, including zinc oxide (ZnO) and 2D transition metal dichalcogenides (TMDs), have been investigated in this dissertation for the realization of high-performance large-area integrated circuits. These novel materials may provide differential advantages over the established large-area thin film technology based on silicon, which has been extensively employed in applications such as large-area flat panel displays, high-speed active matrix thin film circuits, flexible and wearable electronics, etc. The dissertation begins with the discussion of high-performance plasma-enhanced atomic layer deposition (PEALD) of ZnO thin films and ZnO thin film transistors (TFTs) with a field effect mobility of ~ 10 to 20 cm2/Vs, which have been demonstrated. Offset-drain ZnO TFTs, which are able to withstand or switch voltage beyond 80 V, have also been demonstrated. These results shed light on the realization of large-area active-matrix circuits beyond the capabilities of the current display industry where high circuit speed or high operation voltage is required. To further improve the performance of ZnO-based electronics, many related materials, including doped ZnO, zinc nitride, and aluminum nitride, have been investigated. Doped ZnO has been proposed as the carrier injection layer that can improve the conductivity of metal-semiconductor contact in ZnO TFTs. Aluminum-doped ZnO thin films have been deposited using triisobutyl aluminum (TIBA) as the dopant precursor instead of trimethyl aluminum (TMA) in order to improve the uniformity of dopant distribution because TIBA has much lower vapor pressure than TMA. AZO thin films with resistivity ~ 10-2 cm have been achieved by PEALD. Besides, aluminum nitride and zinc nitride thin films have also been studied using PEALD. In addition to the showerhead PEALD system, a novel inductively coupled plasma ALD system has been designed and set up that provides RF power up to 500 W in order to generate a highly reactive nitrogen plasma source and enable the deposition of high-quality metal nitride at relatively low temperature. These metal nitride thin films may provide additional building blocks to enhance the speed and thermal stability of ZnO-based thin film devices and circuits.Owing to their excellent electrical and mechanical properties, 2D-TMD thin films have been studied for flexible electronics applications. High quality MoS2 and WS2 thin films have been achieved via mechanical exfoliation and chemical vapor deposition. To fabricate MoS2- and WS2-based TFTs, a 5-step device fabrication process has been developed, which is compatible to both the conventional rigid substrate and the ~ 4.8 nm thick solution-cast polyimide (PI) flexible substrate. The MoS2 and WS2 TFTs fabricated on PI substrate exhibit a field effect mobility of between 1 to 20 cm2/Vs, which is similar to that of those fabricated on rigid silicon substrate. More importantly, extraordinary mechanical strength and stability have been demonstrated for MoS2 and WS2 TFTs fabricated on PI substrate. A reasonably small degradation in device performance has been observed in these flexible 2D-TMD TFTs under static bending to the radius of ~ 2mm and after cyclic bending up to 100,000 cycles. Finally, attempts to create integratable 2D-TMD circuits have been demonstrated. To realize large-area 2D-TMD based circuits, growth of wafer-scale continuous WSe2 thin films has been demonstrated using metal organic chemical vapor deposition (MOCVD). Deposition has been achieved at as low as 400 C, which allows deposition on glass and polymeric substrate and enables the transfer-free fabrication of WSe2 TFTs and circuits on arbitrary platforms. Patterning and post-growth thickness modulation of continuous WSe2 thin film have been demonstrated using CF4 plasma and O2 plasma, whereby high-speed etching and nanometer-scale film thinning can be realized. With the capability of depositing and patterning wafer-scale WSe2 thin films, an array of p-channel WSe2 TFTs have been fabricated with a field effect mobility of ~0.01 cm2/Vs and an on-off ratio greater than 104.
| Author | : Ngwashi Divine Khan |
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| Release | : 2010 |
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Transparent oxide semiconducting films have continued to receive considerable attention, from a fundamental and application-based point of view, primarily because of their useful fundamental properties. Of particular interest is zinc oxide (ZnO), an n-type semiconductor that exhibits excellent optical, electrical, catalytic and gas-sensing properties, and has many applications in various fields. In this work, thin film transistor (TFT) arrays based on ZnO have been prepared by reactive radio frequency (RF) magnetron sputtering. Prior to the TFT fabrication, ZnO layers were sputtered on to glass and silicon substrates, and the deposition parameters optimised for electrical resistivities suitable for TFT applications. The sputtering process was carried out at room temperature with no intentional heating. The aim of this work is to prepare ZnO thin films with stable semiconducting electrical properties to be used as the active channel in TFTs; and to understand the role of intrinsic point defects in device performance and stability. The effect of oxygen (O2) adsorption on TFT device characteristics is also investigated. The structural quality of the material (defect type and concentration), electrical and optical properties (transmission/absorption) of semiconductor materials are usually closely correlated. Using the Vienna ab-initio simulation package (VASP), it is predicted that O2 adsorption may influence film transport properties only within a few atomic layers beneath the adsorption site. These findings were exploited to deposit thin films that are relatively stable in atmospheric ambient with improved TFT applications. TFTs incorporating the optimised layer were fabricated and demonstrated very impressive performance metrics, with effective channel mobilities as high as 30 cm2/V-1s-1, on-off current ratios of 107 and sub-threshold slopes of 0.9? 3.2 V/dec. These were found to be dependent on film thickness (~15? 60 nm) and the underlying dielectric (silicon dioxide (SiO2), gadolinium oxide (Gd2O3), yttrium oxide (Y2O3) and hafnium oxide (HfO2)). In this work, prior to sputtering the ZnO layer (using a ZnO target of 99.999 % purity), the sputtering chamber was evacuated to a base pressure ~4 x 10-6 Torr. Oxygen (O2) and argon (Ar) gas (with O2/Ar ratio of varying proportions) were then pumped into the chamber and the deposition process optimised by varying the RF power between 25 and 500 W and the O2/Ar ratio between 0.010 to 0.375. A two-level factorial design technique was implemented to test specific parameter combinations (i.e. RF power and O2/Ar ratio) and then statistical analysis was utilised to map out the responses. The ZnO films were sputtered on glass and silicon substrates for transparency and resistivity measurements, and TFT fabrication respectively. For TFT device fabrication, ZnO films were deposited onto thermally-grown silicon dioxide (SiO2) or a high-k dielectric layer (HfO2, Gd2O3 and Y2O3) deposited by a metal-organic chemical deposition (MOCVD) process. Also, by using ab initio simulation as implemented in the?Vienna ab initio simulation package (VASP)?, the role of oxygen adsorption on the electrical stability of ZnO thin film is also investigated. The results indicate that O2 adsorption on ZnO layers could modify both the electronic density of states in the vicinity of the Fermi level and the band gap of the film. This study is complemented by studying the effects of low temperature annealing in air on the properties of ZnO films. It is speculated that O2 adsorption/desorption at low temperatures (150? 350 0C) induces variations in the electrical resistance, band gap and Urbach energy of the film, consistent with the trends predicted from DFT results.
| Author | : Elvira Fortunato |
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| Total Pages | : 337 |
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| Author | : Prem Thapaliya |
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| Total Pages | : 182 |
| Release | : 2016 |
| Genre | : Flat panel displays |
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Conventional amorphous silicon based thin film transistors have been the most widely used ones for flat panel display application during the last two decades. However, the low mobility of less than 1 cm2/Vs and light induced instability of the amorphous silicon based thin film transistor make them unsuitable for high resolution displays. Oxide based thin film transistors have attracted a great deal of interest as an alternative to conventional amorphous silicon based thin film transistors for high resolution display applications. In particular, ZnO has gained considerable interest for the next generation transparent and flexible display due to its wide band gap of 3.37 eV, high electron mobility and low temperature deposition forming good quality of polycrystalline film even at room temperature. Consequently all the aforementioned features of ZnO make them promising channel material for the flexible and transparent TFTs. The electrical characteristics of ZnO based TFTs is greatly affected by the deposition condition and hence crystalline quality of channel layer, thickness of channel layer and quality of interface between the gate dielectric and the channel layer. Therefore, the deposition temperature and the thickness of the ZnO channel needs to be optimized in order to achieve high performance ZnO TFTs. Moreover, the quality of interface between the ZnO channel layer and the gate dielectric is of vital importance to improve the performance of the TFTs. In this dissertation, we have fabricated and characterized RF sputtered ZnO based thin film transistor using high-k HfO2 gate dielectric. The transparent ZnO TFTs was realized using FTO as a transparent gate electrode as opposed to commonly used ITO gate electrode. It was found that TFTs fabricated using the FTO gate electrode showed lower mobility and on/off ratio compared to the TFTs with Ru as a gate on the Si substrate. This deterioration of TFTs performance with the use of FTO gate electrode was attributed to the degradation of HfO2 gate dielectric due to the diffusion of fluorine from the FTO into the HfO2 during its deposition at 300 °C. In order to minimize the interface trap density at the interface between the ZnO and HfO2, an interfacial layer of MgO with different thickness was investigated. It was found that 10 nm MgO is an optimum thickness that can reduce the interface trap density by almost one order of magnitude and hence exhibit the best TFTs performance with field effect mobility, threshold voltage, on/off ratio and subthreshold swing to be 0.3 cm2/V.s, 3.7 V , 106 and 1.35 V/decade respectively. The decrease in the interface trap density with the interfacial layer was attributed to the reduction of defects in the ZnO by the excess oxygen ions of MgO. Furthermore, the ZnO channel layer was deposited at different temperature including room temperature, 50 °C, 100 °C and 200 °C, to determine the optimum deposition temperature that can achieve high performance ZnO TFTs. It was found that ZnO deposited at 50 °C showed the best TFT performance with field effect mobility, threshold voltage, on off ratio and subthreshold swing 1.12 cm2/V.s, 5.8 V, 1.4×105, 1.35 V/decade respectively. The improvement in the performance of the TFTs device with 50 °C ZnO was attributed to the low surface roughness of ZnO film, increased grain size and good polycrystalline quality which was confirmed with the help of XRD, AFM and SEM measurement of ZnO thin film deposited at different temperature. Likewise, once the optimum deposition temperature of ZnO was determined, the effect of ZnO thickness was investigated by depositing the ZnO with different thickness including 30 nm, 50 nm, 70 nm and 100 nm while maintaining the deposition temperature of ZnO to be at 50 °C. It was found that the TFTs device with 50 nm exhibit the superior performance over the other thicknesses of ZnO which was ascribed to the improved polycrystalline quality, low surface roughness of the 50 nm ZnO thin film.
| Author | : Jose Ramirez |
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| Total Pages | : |
| Release | : 2015 |
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Zinc oxide thin film transistors (TFTs) are investigated in this work for large-area electronic applications outside of display technology. A constant pressure, constant flow, showerhead, plasma-enhanced atomic layer deposition (PEALD) process has been developed to fabricate high mobility TFTs and circuits on rigid and flexible substrates at 200 °C. ZnO films and resulting devices prepared by PEALD and pulsed laser deposition (PLD) have been compared. Both PEALD and PLD ZnO films result in densely packed, polycrystalline ZnO thin films that were used to make high performance devices. PEALD ZnO TFTs deposited at 300 °C have a field-effect mobility of ~ 40 cm2/V-s (and > 20 cm2/V-S deposited at 200 °C). PLD ZnO TFTs, annealed at 400 °C, have a field-effect mobility of > 60 cm2/V-s (and up to 100 cm2/V-s). Devices, prepared by either technique, show high gamma-ray radiation tolerance of up to 100 Mrad(SiO2) with only a small radiation-induced threshold voltage shift (VT ~ -1.5 V). Electrical biasing during irradiation showed no enhanced radiation-induced effects. The study of the radiation effects as a function of material stack thicknesses revealed the majority of the radiation-induced charge collection happens at the semiconductor-passivation interface. A simple sheet-charge model at that interface can describe the radiation-induced charge in ZnO TFTs. By taking advantage of the substrate-agnostic process provided by PEALD, due to its low-temperature and excellent conformal coatings, ZnO electronics were monolithically integrated with thin-film complex oxides. Application-based examples where ZnO electronics provide added functionality to complex oxide-based devices are presented. In particular, the integration of arrayed lead zirconate titanate (Pb(Zr, Ti)O3 or PZT) thin films with ZnO electronics for microelectromechanical systems (MEMs) and deformable mirrors is demonstrated. ZnO switches can provide voltage to PZT capacitors with fast charging and slow discharging time constants. Finally, to circumvent fabrication challenges on predetermined complex shapes, like curved mirror optics, a technique to transfer electronics from a rigid substrate to a flexible substrate is used. This technique allows various thin films, regardless of their deposition temperature, to be transferred to flexible substrates. Finally, ultra-low power operation of ZnO TFT gas sensors was demonstrated. The ZnO ozone sensors were optimized to operate with excellent electrical stability in ambient conditions, without using elevated temperatures, while still providing good gas sensitivity. This was achieved by using a post-deposition anneal and by partially passivating the contact regions while leaving the semiconductor sensing area open to the ambient. A novel technique to reset the gas sensor using periodic pulsing of a UV light over the sensor results in less than 25 milliseconds recovery time. A pathway to achieve gas selectivity by using organic thin-film layers as filters deposited over the gas sensors tis demonstrated. The ZnO ozone sensor TFTs and the UV light operate at room temperature with an average power below 1 [mu]W.
| Author | : Hideo Hosono |
| Publisher | : John Wiley & Sons |
| Total Pages | : 644 |
| Release | : 2022-05-31 |
| Genre | : Technology & Engineering |
| ISBN | : 1119715571 |
AMORPHOUS OXIDE SEMICONDUCTORS A singular resource on amorphous oxide semiconductors edited by a world-recognized pioneer in the field In Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory, the Editors deliver a comprehensive account of the current status of—and latest developments in—transparent oxide semiconductor technology. With contributions from leading international researchers and exponents in the field, this edited volume covers physical fundamentals, thin-film transistor applications, processing, circuits and device simulation, display and memory applications, and new materials relevant to amorphous oxide semiconductors. The book makes extensive use of structural diagrams of materials, energy level and energy band diagrams, device structure illustrations, and graphs of device transfer characteristics, photographs and micrographs to help illustrate the concepts discussed within. It also includes: A thorough introduction to amorphous oxide semiconductors, including discussions of commercial demand, common challenges faced during their manufacture, and materials design Comprehensive explorations of the electronic structure of amorphous oxide semiconductors, structural randomness, doping limits, and defects Practical discussions of amorphous oxide semiconductor processing, including oxide materials and interfaces for application and solution-process metal oxide semiconductors for flexible electronics In-depth examinations of thin film transistors (TFTs), including the trade-off relationship between mobility and reliability in oxide TFTs Perfect for practicing scientists, engineers, and device technologists working with transparent semiconductor systems, Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory will also earn a place in the libraries of students studying oxides and other non-classical and innovative semiconductor devices. WILEY SID Series in Display Technology Series Editor: Ian Sage, Abelian Services, Malvern, UK The Society for Information Display (SID) is an international society which has the aim of encouraging the development of all aspects of the field of information display. Complementary to the aims of the society, the Wiley-SID series is intended to explain the latest developments in information display technology at a professional level. The broad scope of the series addresses all facets of information displays from technical aspects through systems and prototypes to standards and ergonomics.
| Author | : Zhigang Zang |
| Publisher | : John Wiley & Sons |
| Total Pages | : 293 |
| Release | : 2023-11-29 |
| Genre | : Technology & Engineering |
| ISBN | : 352784256X |
Metal Oxide Semiconductors Up-to-date resource highlighting highlights emerging applications of metal oxide semiconductors in various areas and current challenges and directions in commercialization Metal Oxide Semiconductors provides a current understanding of oxide semiconductors, covering fundamentals, synthesizing methods, and applications in diodes, thin-film transistors, gas sensors, solar cells, and more. The text presents state-of-the-art information along with fundamental prerequisites for understanding and discusses the current challenges in pursuing commercialization and future directions of this field. Despite rapid advancements in the materials science and device physics of oxide semiconductors over the past decade, the understanding of science and technology in this field remains incomplete due to its relatively short research history; this book aims to bridge the gap between the rapidly advancing research progress in this field and the demand for relevant materials and devices by researchers, engineers, and students. Written by three highly qualified authors, Metal Oxide Semiconductors discusses sample topics such as: Fabrication techniques and principles, covering vacuum-based methods, including sputtering, atomic layer deposition and evaporation, and solution-based methods Fundamentals, progresses, and potentials of p–n heterojunction diodes, Schottky diodes, metal-insulator-semiconductor diodes, and self-switching diodes Applications in thin-film transistors, detailing the current progresses and challenges towards commercialization for n-type TFTs, p-type TFTs, and circuits Detailed discussions on the working mechanisms and representative devices of oxide-based gas sensors, pressure sensors, and PH sensors Applications in optoelectronics, both in solar cells and ultraviolet photodetectors, covering their parameters, materials, and performance Memory applications, including resistive random-access memory, transistor-structured memory devices, transistor-structured artificial synapse, and optical memory transistors A comprehensive monograph covering all aspects of oxide semiconductors, Metal Oxide Semiconductors is an essential resource for materials scientists, electronics engineers, semiconductor physicists, and professionals in the semiconductor and sensor industries who wish to understand all modern developments that have been made in the field.
