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The research on amorphous indium–gallium–zinc oxide (IGZO) Schottky contacts has received much attention for various electronic applications due to their high uniformity, excellent electrical prope...

Various memristor-based synaptic devices have been proposed for implementing a neuromorphic system. However, memristor devices typically suffer from various inherent problems such as nonlinearity a...

Sub-micrometer thin-film transistors (TFTs) are realized using multi-level imprint lithography. Amorphous indium gallium zinc oxide ( $\alpha $ -IGZO) TFTs with channel lengths as small as $0.7~\mu \text{m}$ , field-effect mobility of 10 cm2V−1s−1 and on/off ratio of circa 107 were integrated into a 1000-pixels per inch (ppi) TFT backplane array. The reduction of the number of patterning steps and the inherent self-registration of the most critical transistor layers on top of each other offer a cost-effective high-throughput fabrication route for high-resolution TFT arrays.

We report high performance amorphous Indium-Gallium-Zinc-Oxide ( ${a}$ -IGZO) thin-film transis- tors (TFTs) with 10 nm atomic-layer-deposited HfO2 as the gate dielectric, achieving subthreshold swing ( SS ) of 70.2 mV/decade, high effective mobility ( $\mu _{\textit {eff}}$ ) of 55.3cm2/ $\text{V}\cdot \text{s}$ at an inversion carrier density ( $N_{\textit {inv}}$ ) of $5\times 10^{{12}}$ cm-2, and large $I_{ON}/\text{I}_{OFF}$ of >109. Furthermore, very good device-to-device uniformity has been confirmed by the statistical distribution of SS and maximum transconductance (Gm, max) measured from 20 pristine TFT devices. This ${a}$ -IGZO TFT has immense potential for the ultrafast and low power electronic devices for next-generation cost-effective emissive display, image sensing, and hardware for artificial intelligence (AI).

In this article, the effects of redundant electrode width on stability of inverted staggered via-contact structured amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) under hot-carrier stress (HCS) were investigated. It is found that devices with a larger redundant electrode width have a severer degradation behavior after HCS. Capacitance–voltage measurements were conducted to study the degradation mechanism and technology computer-aided design (TCAD) simulation was employed to understand the different degradation behaviors.

The mobility of pristine amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) is insufficient to meet the requirement of the future ultra-high-definition displays. Reported herein is the fabrication of hydrogenated long-channel IGZO TFTs exhibiting a transconductance and an on/off ratio that are orders of magnitude superior to those of the regular devices. The gate bias stability of the treated IGZO TFTs was greatly enhanced, with the threshold voltage shifting by less than 1 V after 1 h stress. Experimentally, the hydrogenation of the active layer was achieved via the deposition of a SiNx/SiOx bilayer on top of the IGZO via plasma-enhanced chemical vapor deposition followed by post-annealing under optimized conditions. The elemental depth profiles indicated that this enhanced performance originated from the hydrogen doping of the IGZO film. Furthermore, a dual-gate structure was fabricated to alleviate the deterioration of the subthreshold properties induced by the excess hydrogen doping.

We report high performance top-gate amorphous Indium-Gallium-Zinc-Oxide thin film transistors $(\alpha-$ IGZO TFTs) featuring the smallest equivalent oxide thickness (EOT) of sub-1.2 nm among all IGZO-channel TFTs, achieving the highest extrinsic peak transconductance $(G_{m,ext})$ of 62 $\mu \mathrm{S}/\mu \mathrm{m}$ at a drain to source voltage $(V_{DS})=2\mathrm{V}(33.4\mu \mathrm{S}/\mu \mathrm{m}\ \text{at}\ V_{DS}=1\mathrm{V})$ and excellent drain induced barrier lowering (DIBL) of 17.6 m V/V, for a device with a channel length $(L_{CH})$ of 160 nm. The best long channel device has a subthreshold swing (SS) of67.5 mV/decade. This was enabled by using an ultra-scaled 5 nm high-k HfO 2 as the gate dielectric. In addition, temperature study was also performed on $\alpha$ -IGZO TFTs. Field effect mobility $(\mu_{eff})$ show negligible degradation at high temperature, indicating the great potential of $\alpha$ -IGZO TFTs for various emerging applications.

We target the device parameter analysis and drain current modelling for amorphous indium gallium zinc oxide (IGZO) thin film transistors from 210 to 370K. We study and discuss the temperature behaviour of physical IGZO TFT parameters from low to high temperatures. We demonstrated and explained that in IGZO TFTs, the characteristic temperature of the density of states (DOS) increases, with increasing temperature. Finally, using the extracted parameters, we validate our IGZO TFT drain current model at temperatures from 190K up to 370K.

This paper reports the effect of the cation composition on the electrical properties of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) where atomic layer deposition (ALD) was used to deposit an a-IGZO channel layer. The In0.38Ga0.18Zn0.44O transistors at a 200°C annealing temperature exhibited 39.4 cm2/V·s field effect mobility (µFE), −0.12 V threshold voltage (VTH), 0.40 V/decade subthreshold gate swing (SS), and >107 ION/OFF ratio, corresponding to the state-of-the-art characteristics of transistors with a sputtered IGZO channel. Further enhancement of the μFE value was observed for the devices with a higher In fraction: the In0.45Ga0.15Zn0.40O transistor had a higher μFE value of 48.3 cm2/V·s, −4.06 V VTH, 0.45 V/decade SS, and >107 ION/OFF ratio. The cation composition dependence on the performance of the a-IGZO TFTs was explained by analysing the density-of-state (DOS) distribution for the corresponding devices using the experimental independent variable (IV) and theoretical Technology Computer-aided Design (TCAD) simulation.

Plasma damage of indium-gallium-zinc-oxide (IGZO) thin film transistor (TFT) was investigated. The IGZO TFT was fabricated and the performance was measured before and after BCl3 and/or Cl2 plasma treatment to evaluate the IGZO damage. The BCl3 and/or Cl2 plasma deteriorated the IGZO TFT performance significantly even after a short exposure time in the plasma. We propose a new wet etching process to remove a source/drain metal without damaging the underlying IGZO layer. The wet etching process can be utilized for the fabrication of IGZO TFT array using a roll-to-roll process via a self-aligned imprint lithography technique.

In this work, we have reported dual-gate amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs), where a top-gate self-aligned TFTs has a secondary bottom gate and the TFT integration comprises only five mask steps. The electrical characteristics of a-IGZO TFTs under different gate control are compared. With the enhanced control of the channel with two gates connected together, parameters such as on current (ION), sub-threshold slope (SS−1), output resistance, and bias-stress instabilities are improved in comparison with single-gate control self-aligned a-IGZO TFTs. We have also investigated the applicability of the dual-gate a-IGZO TFTs in logic circuitry such as 19-stage ring oscillators.

Proposed herein is a new technique of activation for the backplane of low-temperature amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) by applying a bias voltage to gate, sou...

In this paper, amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) using carbon nanotubes (CNTs) as source/drain/gate electrodes have been proposed and experimentally realized. Effect of the annealing temperature on the contact properties between a-IGZO and single-walled carbon nanotube (SWNT) electrodes, as well as the electrical properties of the a-IGZO TFTs have been investigated. The contact performance between SWNT electrodes and a-IGZO active layer has been improved by increasing the annealing temperature. The resulting a-IGZO TFT with SWNT electrodes shows an effective mobility of 8 cm2/ $\text{V}\cdot {\mathrm{ s}}$ and an on/off current ratio of $1.9\times 10^{7}$ under a drain voltage of 10 V. This SWNT-electrode a-IGZO TFT design makes it possible for CNTs as electrodes of the metal oxide TFT.

Amorphous Indium Gallium Zinc Oxide (IGZO) is an important material which can be used in transparent thin film transistors (TFTs) due to its high field effect mobility for the next generation flat panel displays. Evolution of electrical properties and TFT characteristics of amorphous IGZO thin films synthesized with radio-frequency (RF) sputtering technique with O2 plasma immersion has been studied. The a-IGZO thin film with O2 plasma immersion can greatly enhance the Hall mobility while largely reduce the electron concentration. The influence of post-deposition O2 plasma immersion has been studied. The electrical properties and the transistor performance can be attributed to the repair in the oxygen-related defects of the IGZO thin films. The threshold voltage (Vth) is an important parameter in TFTs performance which is determined by the electron concentration in the transistor channel layer; however it is not easy to control the Vth as the oxygen vacancies which are related to the electron concentration can be easily generated during the fabrication process. An exposure of the back channel of an IGZO TFT to ultraviolet (UV) activated oxygen can effectively shift the Vth of the TFT. There is a linearly relation between the Vth and the exposure time while the on-state current greatly increase with the exposure time. Other TFT parameters such as the field-effect mobility and sub-threshold swing are not significantly affected by the exposure. An exposure to UV-activated oxygen is a simple way to control the Vth, and the TFT can be easily changed from the enhancement mode to the deletion mode with this technique. The effect of the exposure on the Vth is attributed to the increase in the electron concentration of the channel layer as a result of the creation of oxygen vacancies by exposure. Beside UV-activated oxygen exposure treatment, UV light is commonly used in the cleaning process to remove the particles and impurities on the thin film in the TFT fabrication. An UV exposure can cause a shift in the threshold voltage of IGZO TFT, which poses a problem to normal device operation. The effect of short-duration UV exposure on the Vth of amorphous IGZO TFTs and its recovery characteristics are investigated. The illuminated devices showed a slow recovery in threshold voltage without external bias. However, an instant recovery can be achieved by the application of positive gate pulses, which is due to the elimination of the positive trapped charges as a result of the presence of a large amount of field-induced electrons in the interface region. In the last chapter, the memory devices (e.g. non-volatile memory (NVM) and write once read many times memory devices (WORM)) based on O2 plasma-treated IGZO thin films has been demonstrated. The WORM device has a normally-OFF state with a very high resistance as a result of the O2 plasma treatment on the IGZO thin films. The device could be switched to an ON state with a low resistance by applying a voltage pulse. The WORM device has good data-retention and reading-endurance capabilities. DOCTOR OF PHILOSOPHY (EEE)

Thermoelectric (TE) devices are promising candidates for renewable energy resources. Superior TE materials are achieved by obtaining high power factors (PF = S 2 s), where S is the Seebeck coefficient, s is the electrical conductivity. Recently, it is necessary to investigate flexible TE devices for harvesting distributed energy at room temperature. On the other hands, amorphous InGaZnO(a-IGZO) has been already in practical use as a TFT device. The a-IGZO has enormous potential such as transparent, a low temperature process, controllability of the carrier concentration and so on. However, a few studies have been conducted on the TE properties of IGZO. Therefore, I consider a-IGZO can be applied to a transparent flexible TE element by optimizing the TE properties. There is a trade-off between the S and sunder variation of the carrier concentration. Optimization of the carrier concentration is important for a high performance TE material. In this study, I optimized the carrier concentration in a-IGZO thin film and evaluated the effects of oxygen ratio on the TE properties. In addition, the obtained TE properties were theoretically analyzed. At first, a-IGZO films (200 nm) were deposited on a glass substrate at 300 K using RF magnetron sputtering. During the sputtering process, the oxygen flow ratio (O2/(Ar + O2)) was set at values of 0 ~ 6 %. After the sputtering process, the samples were annealed at 300 °C for 2 h in a N2 atmosphere. After annealing, Mo electrodes were formed. TE properties such as S and s were measured in the range of 100 K ~ 400 K by physical property measurement system (PPMS). Carrier concentration (n) was measured by Hall effect method at room temperature. To analyze the measured data, I utilized percolation model that the potential barrier hinders conduction for electron transmission when the Fermi level (E f ) is located in the tail-states. E f , and other physical parameters were obtained by fitting theoretical equations to the measured S and s. The measured s and S with theoretical results are compared. The s increased and S decreased with decreasing oxygen flow ratio. The fitting was performed in the temperature range from 150 to 350 K. The theoretical results of s fit well with the experimental results. The fitting results of S show good agreement around low temperature and under the higher oxygen flow ratios, the measured S was slightly different from the theoretical result because of nondegenerated behavior. Carrier concentration with dependence of S and s shows the relationship of the trade off between S and s . The carrier concentration increased with decreasing oxygen flow ratio. This result can be adequately explained by the internal defects resulted from the increment of oxygen vacancies. PF showed a gradual increase along with the carrier concentration up to ~ 7.7 × 1019 cm−3 and then decreased. Therefore, the PF has the maximum value of 0.082 × 10-3 W / mK2. Figure 3 indicates a trend for E f to increase with increasing carrier concentration. It was confirmed that the obtained value of E f by fitting at which PF was maximal was equivalent to the potential barrier height. These finding leads to a conclusion that the TE properties o a-IGZO were controlled by the relationship between E f and the potential barriers. The TE properties of a-IGZO thin films were evaluated with controlled carrier concentrations to obtain better TE properties. By optimizing the carrier concentration, I found that the PF had a maximal value of 0.082 × 10−3 W/mK2 at 300 K. This optimized PF was larger than the value of the previous report. Theoretical analysis revealed the relationship of E f with PF.

Recent advances in glucose sensing have focused on the integration of sensors into contact lenses to allow noninvasive continuous glucose monitoring. Current technologies focus primarily on enzyme-based electrochemical sensing which requires multiple nontransparent electrodes to be integrated. Herein, we leverage amorphous indium gallium zinc oxide (IGZO) field-effect transistors (FETs), which have found use in a wide range of display applications and can be made fully transparent. Bottom-gated IGZO-FETs can have significant changes in electrical characteristics when the back-channel is exposed to different environments. We have functionalized the back-channel of IGZO-FETs with aminosilane groups that are cross-linked to glucose oxidase and have demonstrated that these devices have high sensitivity to changes in glucose concentrations. Glucose sensing occurs through the decrease in pH during glucose oxidation, which modulates the positive charge of the aminosilane groups attached to the IGZO surface. The change in charge affects the number of acceptor-like surface states which can deplete electron density in the n-type IGZO semiconductor. Increasing glucose concentrations leads to an increase in acceptor states and a decrease in drain-source conductance due to a positive shift in the turn-on voltage. The functionalized IGZO-FET devices are effective in minimizing detection of interfering compounds including acetaminophen and ascorbic acid. These studies suggest that IGZO FETs can be effective for monitoring glucose concentrations in a variety of environments, including those where fully transparent sensing elements may be of interest.

In spite of its high field effect mobility, the a-IGZO TFT’s instability induced by the light illumination and the gate voltage (Vg ) stress is a crucial concern in many electrical and optical applications [1-4]. The wavelength of the illumination light affects the subthreshold swing (S) and threshold voltage (Vth ) [5,6]. In this paper, authors study the defects generation and self-repair phenomena in the a-IGZO TFT under the UV illumination and gate bias stress condition. The inverted, staggered, tri-layer a-IGZO TFT was fabricated on a glass substrate, as shown in Figure 1. The SiOx gate dielectric layer was deposited by PECVD. The 50 nm-thick a-IGZO semiconductor layer was sputtered deposited from an In2O3:Ga2O3:ZnO (1:1:1 mole ratio) target at room temperature. The etch stopper (ES) layer was composed of SiOx (200 nm-thick)/AlOx (20 nm-thick). The source and drain electrodes were made of the Ti/Al/Ti stack. The passivation layer was made of PECVD SiOx (100 nm-thick)/SiNx (100 nm-thick). The a-IGZO TFT was stressed under UV (λ = 395 nm, 0.3 mW cm−2) for 30 min, i.e., UVS (no Vg bias), PBUVS (Vg = 20V, Vd = 0V), or NBUVS (Vg = -20V, Vd = 0V) for 30 minutes at room temperature. Then, the TFT was stored in dark at room temperature or heated to 200°C, followed by measurement of transfer characteristics at V DS = 0.1 V periodically. Figure 2 shows curves of DS vs. relaxation time, i.e., time after releasing the stress condition, at room temperature. Without gate bias, the DS drop was large at the beginning and small later on, i.e., 92% vs. 4%. For the PBUVS stressed TFT, the DS vs. time curve overlaps with that of the UVS stressed TFT. Therefore, defects on the gate dielectric interface were of two types, i.e., quickly or slowly self-repaired. For the NBUVS stressed TFT, defects were recovered in three stages. In the first 5 minutes, they were reduced by 59%. In the next 330 minutes, they were slightly reduced. After 200 hr, they were completely removed. Although at the beginning, the DS of the NBUVS TFT was smaller than that of the UVS or PBUVS TFT, the defect recovery rate of the former was much slower than that of the latter. Separately, the DS vs. relaxation time curve was measured at 200°C. For the UVS or PBUVS stressed TFTs, the S was restored to the original, unstressed value in less than 5 minutes. However, for the NBUVS stressed TFT, the restoring of S progressed in two stages from different mechanisms. The UV illumination caused the negative shift of the V th and increase of S. Defects were created and saturated at the gate dielectric interface as well as in the bulk a-IGZO layer within a short period of UV exposure. The addition of the positive Vg did not affect the mechanism of the defect-generation. Majority of these defects were loosely trapped and could be self-repaired after being stored shortly in dark at room temperature. Defects generated by the NBUVS were difficult to self-repair. At 200°C, all defects were removed in a short period of time. In summary, under the UV illumination condition, the polarity of the bias Vg determines the type of defects generated in the TFT. More detailed discussions on mechanisms of defects generation and repair will be presented. This study provides important information on the reliability the a-IGZO TFT, which is critical to real world applications. Authors acknowledge Prof. Ting-chang Chang, Department of Physics of National Sun Yat-sen University, Kaohsiung, for providing samples. Jingxin Jiang thanks the Doctoral Scientific Research Foundation of Liaoning Province (project No. 201601156), National Natural Science Foundation of China (project No. 6187011861), and China Scholarship Council for proving financial support for her visit to Thin Film Nano and Microelectronics Laboratory, Texas A&M University through the Postdoctoral Research Program. [1] H. Oh, et al., Appl. Phys. Lett. 97, 183502 (2010). [2] J. Jiang, et al., Appl. Phys. Express 7, 114103 (2014). [3] H. Lu, et al., IEEE J. Electron Devices Soc. 5, 504 (2017). [4] T. C. Fung, et al., J. Inf. Display 9, 21 (2008). [5] X. Huang, et al., Appl. Phys. Lett. 100, 243505 (2012). [6] T. Chen, et al., J. Phys. D: Appl. Phys. 50, 42LT02 (2017). Figure 1

Persistent photoconductivity (PPC) effect and its light-intensity dependence of both enhancement and depletion (E-/D-) mode amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) are systematically investigated. Density of oxygen vacancy (VO) defects of E-mode TFTs is relatively small, in which formation of the photo-induced metastable defects is thermally activated, and the activation energy (E a) decreases continuously with increasing light-intensity. Density of VO defects of D-mode TFTs is much larger, in which the formation of photo-induced metastable defects is found to be spontaneous instead of thermally activated. Furthermore, for the first time it is found that a threshold dose of light-exposure is required to form fully developed photo-induced metastable defects. Under low light-exposure below the threshold, only a low PPC barrier is formed and the PPC recovery is fast. With increasing the light-exposure to the threshold, the lattice relaxation of metal cations adjacent to the doubly ionized oxygen vacancies ( V O 2 + ) is fully developed, and the PPC barrier increases to ∼ 0.25 eV, which remains basically unchanged under higher light-exposure. Based on the density of VO defects in the channel and the condition of light illumination, a unified model of formation of photo-induced metastable defects in a-IGZO TFTs is proposed to explain the experimental observations.

For the purpose of improving reliability of our high-sensitivity pH sensor based on the top-gate effect in amorphous indium-gallium-zinc oxide thin-film transistor (a-InGaZnO TFT), we propose extended-gate a-InGaZnO TFT pH sensor having an ALD-AlOx/sputtered-TaOx layered top-gate insulator and a Ti extended-gate electrode. Unlike our previous insulated-gate a-InGaZnO TFT pH sensor, we do not need to immerse the TFT sensor device into the solution, and thus we could expect improvement of its reliability. We discuss our primary results for the extended-gate a-InGaZnO TFT pH sensor, including its pH sensitivity and response to a pH change of 0.05.

© 2018 American Physical Society. Based on a rational classification of defects in amorphous materials, we propose a simplified model to describe intrinsic defects and hydrogen impurities in amorphous indium gallium zinc oxide (a-IGZO). The proposed approach consists of organizing defects into two categories: point defects, generating structural anomalies such as metal - metal or oxygen - oxygen bonds, and defects emerging from changes in the material stoichiometry, such as vacancies and interstitial atoms. Based on first-principles simulations, it is argued that the defects originating from the second group always act as perfect donors or perfect acceptors. This classification simplifies and rationalizes the nature of defects in amorphous phases. In a-IGZO, the most important point defects are metal - metal bonds (or small metal clusters) and peroxides (O-O single bonds). Electrons are captured by metal - metal bonds and released by the formation of peroxides. The presence of hydrogen can lead to two additional types of defects: metal-hydrogen defects, acting as acceptors, and oxygen-hydrogen defects, acting as donors. The impact of these defects is linked to different instabilities observed in a-IGZO. Specifically, the diffusion of hydrogen and oxygen is connected to positive- and negative-bias stresses, while negative-bias illumination stress originates from the formation of peroxides. ispartof: PHYSICAL REVIEW APPLIED vol:9 issue:5 status: published

A compact model of amorphous indium gallium zinc oxide thin-film transistors, suitable for CAD simulators, is proposed. The model is simple, symmetric, and accurately accounts for the subthreshold, linear, and saturation regimes via a unique formulation. It accounts for both trapped and free charges by means of multiple-trapping-and-release and percolation in the conduction band. Aim of the paper is to work out the analytic expression of the current and of the terminal charges, along with the surface potential and the electric field as a function of position in the channel. The availability of the surface potential and of the electric field is the key to model advanced physical effects as, for example, the carrier injection from the electrodes into the channel.

Device performance of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) has been improved greatly by using bovine serum albumin (BSA) as the top gate dielectric. BSA is a natural protein with acidic and basic amino acid residues, which is easily hydrated in air ambient. A typical a-IGZO TFT with hydrated BSA as the top gate dielectric exhibits a field-effect mobility ( μ FE ) value of 113.5 cm 2 V −1 s −1 in saturation regime and a threshold voltage ( V TH ) value of 0.25 V in air ambient. The excellent device performance can be well explained by the formation of electric double layers (EDLs) near the interfaces of a-IGZO/hydrated BSA and hydrated BSA/gate electrode. The reliability issue of a-IGZO TFTs gated with hydrated BSA has been also investigated by using the life time test without encapsulation. The V TH value increases and μ FE,sat value reduces slightly for the a-IGZO TFT and remain stabilized over 60 days.

This paper reports on an InGaZnO optical study by spectrometric ellipsometry. First of all, the fitting results of different models and different structures are analysed to choose the most appropriate model. The Tauc–Lorentz model is suitable for thickness measurements but a more complex model allows the refractive index and extinction coefficient to be extracted more accurately. Secondly, different InGaZnO process depositions are carried out in order to investigate stability, influence of deposition time and uniformity. Films present satisfactory optical stability over time. InGaZnO optical property evolution as a function of deposition time is related to an increase in temperature. To understand the behaviour of uniformity, mapping measurements are correlated to thin film resistivity. Results show that temperature and resputtering are the two phenomena that affect IGZO uniformity.