HfInZnO Thin Film Transistors Research Articles

Investigation of the electrical properties and stability of HfInZnO thin-film transistors

In this study, amorphous HfInZnO (a-HIZO) thin films and related thin-film transistors (TFTs) were fabricated using the RF-sputtering method. The effects of the sputtering power (50–200 W) on the structural, surface, electrical, and optical properties of the a-HIZO films and the performance and NBIS stability of the a-HIZO TFTs were investigated. The films’ Ne increased and resistivity decreased as the sputtering power increased. The 100 W deposited a-HIZO film exhibited good optical and electrical properties compared with other sputtering powers. Optimization of the 100 W deposited a-HIZO TFT demonstrated good device performance, including a desirable μFE of 19.5 cm2/Vs, low SS of 0.32 V/decade, low Vth of 0.8 V, and high Ion/Ioff of 107, respectively. The 100 W deposited a-HIZO TFT with Al2O3 PVL also exhibited the best stability, with small Vth shifts of -2.2 V during NBIS testing. These high-performance a-HIZO thin films and TFTs with Al2O3 PVL have practical applications in thin-film electronics.

The Effect of Drain Bias Stress on the Instability of Turned-OFF Amorphous HfInZnO Thin-Film Transistors Under Light Irradiation

A comprehensive study was done regarding stabilities under simultaneous stress of light and negative gate bias ( $V_{\mathrm{ G}}$ )/positive drain bias ( $V_{\mathrm{ D}}$ ) in amorphous hafnium-indium–zinc-oxide thin-film transistors. Negative threshold voltage ( $V_{\mathrm {\mathbf {th}}}$ ) shift was observed in transfer characteristics after the stress. Through the consecutive stresses of ( $V_{\mathrm{G}}= -5$ V, $V_{\mathrm{D}}= 15$ V, and $V_{\mathrm{ S}}= 0$ V) and ( $V_{\mathrm{G}}= -5$ V, $V_{\mathrm{D}}= 0$ V, and $V_{\mathrm{S}}= 15$ V) under light illumination, it is found that the negative $V_{\mathrm {\mathbf {th}}}$ shift is affected only by $V_{\mathbf {G}}$ , because the drain current is determined by source-side energy barrier though drain-side energy band is locally lowered by $V_{\mathrm{D}}$ -induced drain-side trapped holes. Furthermore, the drain-side trapped holes increase ON-current by reducing channel resistance after channel accumulation. Gate-to-drain capacitance ( $C_{\mathrm {\mathbf {GD}}}$ ) was measured before/after the ( $V_{\mathrm{G}}= -5$ V, $V_{\mathrm{D}}= 15$ V, and $V_{\mathrm{S}}= 0$ V) stress to clarify the presence and distribution of the drain-side trapped holes. From $C_{\mathrm {\mathbf {GD}}}$ stretching out after the stress, it is revealed that the trapped holes introduce an additional capacitance by responding to the accumulated electrons and the capacitance is distributed according to the vertical electric field distribution of the stress.

A strategy for performance enhancement of HfInZnO thin film transistors using a double-active-layer structure

We investigate the electrical performance and negative bias stability of thin film transistors (TFTs) using double active layer. Double active layer is consisting of low oxygen content HfInZnO film as bottom channel and high oxygen content HfInZnO film as back channel. The HfInZnO-TFT with double channel layer shows a high mobility of 6.8cm2/Vs, a low threshold voltage of −0.3V, and a threshold voltage shifts of 0.65V under −20V gate bias for 7200s. The results suggest that HfInZnO with low oxygen content as the bottom channel could provide high carrier concentration and good HfInZnO/Al2O3 interface to improve field-effect mobility and negative bias stress stability. HfInZnO with high oxygen content as back channel can control the conductivity to reduce the off current of TFT. Thus, a double-active-layer structure is an effective way to improve the electrical performance of HfInZnO-TFT.

Amorphous HfInZnO Thin Film Transistors for Use in Harsh Environment

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3.4L: Late‐News Paper: Physical Model and Simulation Platform for High‐Level Instability‐Aware Design of Amorphous Oxide Semiconductor Thin‐Film Transistors

AbstractThe negative bias illumination stress (NBIS)‐induced VT instability of amorphous InGaZnO thin‐film transistors (TFTs) is quantitatively investigated and a shallow donor state‐creation model is proposed as a physical mechanism. Furthermore, the difference between InGaZnO and HfInZnO TFTs in perspective of NBIS‐induced instability is consistently elucidated. We expect that the proposed model and simulation platform are potentially powerful tools for high‐level instability‐aware design of oxide TFT devices and circuits.

Influence of a highly doped buried layer for HfInZnO thin-film transistors

Hafnium–indium–zinc oxide (HIZO) channel thin-film transistors (TFTs) have been reported with a 12 nm thick indium–zinc oxide (IZO)-buried layer. IZO-buried HIZO TFTs show excellent electrical characteristics and stabilities such as a high mobility (µFE) of ∼41.4 cm2 V−1 s−1 which is three times higher than that of conventional HIZO TFTs and significantly enhanced bias-temperature-induced stability. High mobility could be obtained since the current path is mainly formed on a highly conductive buried layer with a high carrier concentration over 1018 cm−3. Enhanced stability could be achieved mainly because the generation of the additional trap state was considerably reduced near the drain region due to a relatively short path since the current flows vertically from a highly conductive buried layer to a drain electrode through the HIZO channel via a relatively low carrier density region.

Influence of Hf contents on interface state properties in a-HfInZnO thin-film transistors with SiNx/SiOx gate dielectrics

We evaluated the interface properties of amorphous hafnium–indium–zinc–oxide (a-HIZO) thin-film transistors (TFTs) with respect to various Hf contents. To this end, the subthreshold swing and the low-frequency noise (LFN) of the a-HIZO TFTs were measured and compared. From LFNs providing more accurate information, we quantitatively analyzed the interface trap densities and found that they decrease with increasing Hf contents. Although the acceptor-like tail state densities in bulk channel increase with Hf contents, higher Hf contents show lower threshold voltage shift under bias stress, implying that reliability characteristics of a-HIZO TFTs are more sensitive to interface quality rather than bulk property.

35.1: 14‐inch AMOLED TV Driven by HfInZnO Thin‐Film Transistors

AbstractA full‐color 14‐inch active matrix organic light emitting diode (AMOLED) TV, which does not suffer from the well‐known pixel non‐uniformity of luminance using a simple pixel circuit design consisting of 3 transistors and 1 capacitor, has been developed using amorphous hafnium‐indium‐zinc oxide (a‐HIZO) thin‐film transistors (TFTs) as an active‐matrix backplane. The n‐channel a‐HIZO TFTs exhibit a field‐effect mobility of 10 cm2/V‐s, threshold voltage of 0.38V, on/off ratio of >108, and subthreshold gate swing of 0.21 V/decade. Notably, the long‐ and short‐range standard deviations for the threshold voltage were less than 0.1V and 0.02V, respectively.

Effect of hafnium addition on the electrical properties of indium zinc oxide thin film transistors

This study reports the performance and stability of hafnium–indium zinc oxide (HfInZnO) thin film transistors (TFTs) with thermally grown SiO2. The HfInZnO channel layer was deposited at room temperature by a co-sputtering system. We examined the effects of hafnium addition on the X-ray photoelectron spectroscopy properties and on the electrical characteristics of the TFTs varying the concentration of the added hafnium. We found that the transistor on–off currents were greatly influenced by the composition of hafnium addition, which suppressed the formation of oxygen vacancies. The field-effect mobility of optimized HfInZnO TFT was 1.34 cm 2 V −1 s −1, along with an on–off current ratio of 10 8 and a threshold voltage of 4.54 V. We also investigated the effects of bias stress on HfInZnO TFTs with passivated and non-passivated layers. The threshold voltage change in the passivated device after positive gate bias stress was lower than that in the non-passivated device. This result indicates that HfInZnO TFTs are sensitive to the ambient conditions of the back surface.

The Effect of Dynamic Bias Stress on the Photon-Enhanced Threshold Voltage Instability of Amorphous HfInZnO Thin-Film Transistors

The electrical stability of amorphous HfInZnO (HIZO) thin-film transistors (TFTs) was investigated under static and dynamic stress conditions, with simultaneous visible light radiation. The extent of device degradation is found to be strongly sensitive to the gate voltage, pulse duty ratio, pulse frequency, and exposure to visible light. Dynamic stress experiments demonstrate that highly stable devices can be realized by adjusting the pulse duty ratio and frequency, which suggests that amorphous HIZO TFTs are a promising candidate of switching devices for large-area high-resolution AMLCD applications.

The influence of sputtering power and O2/Ar flow ratio on the performance and stability of Hf–In–Zn–O thin film transistors under illumination

The performance and stability of amorphous HfInZnO thin film transistors under visible light illumination were studied. The extent of device degradation upon negative bias stress with the presence of visible light is found to be strongly sensitive to the extent of photoelectric effect in the oxide semiconductor. Highly stable devices were fabricated by optimizing the deposition conditions of HfInZnO films, where the combination of high sputtering power and high O2/Ar gas flow ratio was found to result in the highest stability under bias stress experiments.

Low Voltage, High Performance Thin Film Transistor with HfInZnO Channel and HfO[sub 2] Gate Dielectric

We fabricated thin film transistors (TFTs) using HfInZnO thin films as active channel layers. The thin films of HfInZnO were deposited by co-sputtering from and InZnO targets. The HfInZnO TFTs were investigated according to the radio-frequency power applied to the target. The transistor on and off currents were greatly influenced by the composition of Hf atoms suppressing the formation of oxygen vacancies. The electrical characteristics of the TFTs show a field-effect mobility of , a threshold voltage of 1.28 V, an on/off ratio of , and a subthreshold swing of 95 mV/dec.