InGaZnO Thin Film Research Articles

Contact Performance and Thermal Stability Improvement of Amorphous InGaZnO Thin-Film Transistors by Using a Buffer/Cu/Buffer Source/Drain Electrode Structure

This paper discussed the contact characteristics and thermal stability of a-IGZO TFT with various kinds of buffer/Cu/buffer electrode structure. The work found that the a-IGZO TFTs with Cu electrode and Mo/Cu/Mo electrode show worse thermal stability than these with ITO/Cu/ITO electrode. The work speculates that the contact performance deterioration after post-anneal was due to Cu oxidation and an interface separation between Mo and Cu, respectively. The work used the G-function method to discuss the contact performance of a-IGZO TFTs with the different kinds of S/D electrodes. The a-IGZO TFT with an ITO/Cu/ITO electrode shows a smaller contact resistance than the other TFTs and had an ohmic contact between the a-IGZO and ITO. In terms of thermal stability and contact performance, ITO/Cu/ITO electrode is a better choice than Mo/Cu/Mo electrode.

Room-Temperature Ozone Sensing Capability of IGZO-Decorated Amorphous Ga2O3 Films.

In present work, we report a room-temperature ozone sensor using InGaZnO (IGZO)-decorated amorphous Ga2O3 (a-Ga2O3) thin films. The gas sensing tests demonstrate that the topmost IGZO modification can significantly promote the sensors' responsivity. Intriguingly, the sensing capability presents a first increasing and then decreasing tendency as the surface morphology of IGZO develops from dispersed particles to a continuous film. Finite difference time domain (FDTD) simulation results prove that IGZO nanoparticles can remarkably increase the surface density of photogenerated electrons, clearly manifesting a strong dependence on IGZO particle size and contributing to the boosted responsiveness. However, once IGZO particles coalesce into a thin film, the ozone sensor's responsivity starts to decrease even though the number of photogenerated carriers still increases. The smaller specific surface area of IGZO thin film is believed to be responsible for this phenomenon. The proposed ozone gas sensors own the merits of low cost, room-temperature detection, easy integration, and mass production, significantly expanding the application fields of a-Ga2O3 thin film.

Significant Performance Enhancement of Very Thin InGaZnO Thin-Film Transistors by a Self-Assembled Monolayer Treatment

The use of amorphous InGaZnO (IGZO) has become more and more popular especially in display technologies because of its high mobility, excellent large area uniformity, and low-temperature processabi...

Back-Channel-Etched InGaZnO Thin-Film Transistors with Au Nanoparticles on the Back Channel Surface

Back-Channel-Etched InGaZnO Thin-Film Transistors with Au Nanoparticles on the Back Channel Surface

Oxygen-related Reliability of Amorphous InGaZnO Thin Film Transistors

Effects of oxygen flow on positive bias temperature instability and hot carrier injection are investigated in Amorphous InGaZnO (IGZO) thin film transistors. The oxygen flow can suppress the oxygen vacancy density, but introduce shallow states near the conduction edges. The electron can tunnel into gate oxide via these shallow states. As a result, the IGZO channel with oxygen flow has more electrons trapped in the gate oxide than the channel without oxygen flow, leading to more positive V T shift after positive bias temperature instability. The IGZO without oxygen flow create oxygen vacancy (VO) in the channel. The hole generated by impact ionization during the hot electron injection can be trapped in VO to form $\text{V}_{\text{O}}^{2+}$ . The $\text{V}_{\text{O}}^{2+}$ leads to less positive V T shift for IGZO channel without oxygen flow than with the oxygen flow. Since the impact ionization occurs near the drain, the positive $V_{T}$ shift of the reverse measurement (VSD > 0) is smaller than the forward measurement (VDS > 0) after hot electron injection.

Device performances and instabilities of the engineered active layer with different film thickness and composition ratios in amorphous InGaZnO thin film transistors

The device performances and instabilities of the engineered active layer with different film thickness and composition ratios in amorphous InGaZnO thin film transistor prepared by RF-sputtering have been investigated. The engineered active layer devices were composed of an In and Zn rich front layer with thickness of 10 nm and a Ga rich back layer with thickness from 20 to 30 nm. The device instabilities were investigated under positive bias stress (PBS), negative bias illumination stress (NBIS) and high VGS and VDS stress. The device performances and the stability have been enhanced in channel engineered active layer a-IGZO TFTs due to the combination of the high conductive channel with In and Zn rich front layer and the passivation effects with the Ga rich back layer. The concurrent device degradation mechanism is suggested to explain the more severe device degradation under high VGS and VDS stress than the device degradation under PBS.

Abnormal threshold voltage shift caused by trapped holes under hot-carrier stress in a-IGZO TFTs

In the investigation of the reliability of a back-channel-etching type amorphous InGaZnO thin film transistor, we found that hot carrier stress has caused an abnormal parallel negative threshold voltage shift in the ID–VG measurement. An electrical measurement method named drain stress was established to investigate this instability. Through the analysis of recovery behavior, gate bias stress and Silvaco simulation, we confirmed that holes from the drain side inject into the passivation layer and/or back-channel interface region rather than into the gate insulator under the transverse electric field. A physical model is proposed to verify this electrical degradation behavior. This work demonstrates that drain stress is valuable in examining the quality of the passivation layer in thin film transistors.

Cluster Size Control toward High Performance Solution Processed InGaZnO Thin Film Transistors

Clusters in a precursor solution play an important role in metal oxide semiconductor films. Additives including acetic acid (AcOH) and acetylacetone (acac) were applied in a precursor solution to a...

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Positive Bias-Stress Stability of Flexible Amorphous InGaZnO Thin Film Transistors with Double-Stacked Gate Insulators

Investigating the Back-Channel Effect and Asymmetric Degradation Under Self-Heating Stress in Large Size a-InGaZnO TFTs

This paper investigates the back-channel effect and asymmetric degradation of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) with a bottom-gate structure under self-heating stress (SHS). In our experiments, the phenomenon initially discovered is that for wide-channel devices, the SHS causes the threshold voltage of the minor channel to shift negatively and the main channel to shift positively in the linear region of the I-V curve. Moreover, the results show that these wider devices also have an obvious asymmetric degradation in the saturation region of the I-V curve. Several experiments are used to examine these abnormal phenomena, including AC self-heating stress applied to the drain and SHS at 77 K environment to verify that sufficient thermal energy exists in the active layers to induce the dual-channel effect and asymmetric deterioration. Silvaco TCAD is also used to simulate the electric field of the system and verify our supposition of the asymmetric degradation phenomenon and explain the physical mechanism in the a-IGZO TFTs.

Electrical Performance and Bias-Stress Stability of Amorphous InGaZnO Thin-Film Transistors with Buried-Channel Layers

To improve the electrical performance and bias-stress stability of amorphous InGaZnO thin-film transistors (a-IGZO TFTs), we fabricated and characterized buried-channel devices with multiple-stacked channel layers, i.e., a nitrogen-doped a-IGZO film (front-channel layer), a conventional a-IGZO film (buried-channel layer), and a nitrogen-doped a-IGZO film (back-channel layer). The larger field-effect mobility (5.8 cm2V−1s−1), the smaller subthreshold swing value (0.8 V/dec, and the better stability (smaller threshold voltage shifts during bias-stress and light illumination tests) were obtained for the buried-channel device relative to the conventional a-IGZO TFT. The specially designed channel-layer structure resulted in multiple conduction channels and hence large field-effect mobility. The in situ nitrogen-doping caused reductions in both the front-channel interface trap density and the density of deep states in the bulk channel layers, leading to a small subthreshold swing value. The better stability properties may be related to both the reduced trap states by nitrogen-doping and the passivation effect of the nitrogen-doped a-IGZO films at the device back channels.

Pulsed laser deposition of amorphous InGaZnO4 as an electron transport layer for perovskite solar cells

Hybrid perovskite solar cells (PSCs) have been intensively studied in recent years because of their high efficiency and low costs. For PSCs, the electron transport layer (ETL) is a key for its photoelectric conversion efficiency. Here we demonstrate the application of amorphous InGaZnO4 thin films as ETL for efficient PSCs by pulsed laser deposition (PLD). The PSC device using such InGaZnO4 amorphous film as ETL has achieved an efficiency of 15.1%. The outstanding performance is attributed to the excellent properties of amorphous InGaZnO4 oxide thin films, including high electron mobility and high transparency, what is more, the electronic properties of the films can be controlled by changing the partial pressure of oxygen in the deposition chamber and post-deposition annealing process. Our result will be helpful for preparation of large area PSCs and other opto-electric devices at low temperature by physical vapor deposition method.

Effect of Oxygen Content on Current Stress-Induced Instability in Bottom-Gate Amorphous InGaZnO Thin-Film Transistors.

The effect of oxygen content on current-stress-induced instability was investigated in bottom-gate amorphous InGaZnO (a-IGZO) thin-film transistors. The observed positive threshold voltage shift (ΔVT) was dominated by electron trapping in the gate insulator (GI), whereas it was compensated by donor creation in a-IGZO active regions when both current flows and a high lateral electric field were present. Stress-induced ΔVT increased with increasing oxygen content irrespective of the type of stress because oxygen content influenced GI quality, i.e., higher density of GI electron traps, as well as typical direct current (DC) performance like threshold voltage, mobility, and subthreshold swing. It was also found that self-heating became another important mechanism, especially when the vertical electric field and channel current were the same, independent of the oxygen content. The increased ΔVT with oxygen content under positive gate bias stress, positive gate and drain bias stress, and target current stress was consistently explained by considering a combination of the density of GI electron traps, electric field relaxation, and self-heating-assisted electron trapping.

Device performances and instabilities of channel engineered amorphous InGaZnO thin film transistors

A channel engineered amorphous InGaZnO thin film transistor which is composed of two active channel layers according to the composition ratio and thickness is suggested to enhance the device performance and the device stability. To investigate the annealing treatment on the device performance and instability, conventional thermal annealing and microwave annealing treatments were conducted. The device performances of channel engineered devices are enhanced due to the increased electron concentrations which result from high In contents in the bottom active layer. The device stability is improved due to the combination effects of passivation with top back channel and the high effective barrier height with bottom active layer. Also, the devices treated by microwave annealing show improved device performances and stability.

Effects of electrode materials on the device performances and instabilities in amorphous InGaZnO thin film transistors

The effects of electrode materials on the device performances and instabilities in amorphous InGaZnO thin film transistors (a-IGZO TFTs) have been investigated. The dependences of the source and drain resistance (RSD) and the effective channel length (Leff) on the gate biases were explained by the accumulation layer under the gate overlap (LGOV) which was formed due to the oxygen out diffusion from the channel layer. The RSD with electrode materials is determined by not only workfunction (ΦM) but the electrical property of the metal oxide formation. From the threshold voltage shifts with different electrode materials under positive gate bias stress (PBS), the more device degradation could occur when the more electrons are accumulated in LGOV.

Low-Frequency Noise in Electric Double Layer InGaZnO Thin-Film Transistors Gated with Sputtered SiO2-Based Electrolyte

Using electrolyte as the gate dielectric to form an electric double layer (EDL) is an effective method to reduce the operating voltage of thin-film transistors (TFTs). Such TFTs are typically able ...

P‐3: A Study on the Hot Carrier Effect in InGaZnO Thin Film Transistors

This study provides the most plausible origin of the drain current drop (DCD) phenomenon by hot carrier effect in InGaZnO thin film transistors (IGZO‐TFTs). The degraded performance of IGZO‐TFTs after the DCD phenomenon was related to the charge trapping and modification of the electronic structure by collision of an IGZO matrix with hot carriers.

Ultraviolet laser damage mechanisms of amorphous InGaZnO4 thin films

Laser annealing is a usual step in the process to improve the performance of amorphous InGaZnO4 (a-IGZO) thin film transistors (TFTs). However, a high energy laser will induce damage to a-IGZO thin films during annealing. Knowing laser induced damage thresholds (LIDT) and the mechanisms of a-IGZO thin films helps to use appropriate laser energy density during annealing to avoid damage to the thin films and to achieve the best TFTs’ properties. In this article, the ultraviolet laser with a wavelength of 355 nm and a pulse width of 7.7 ns LIDT and damage mechanisms of a-IGZO thin films are reported. The damage morphologies are characterized with optical microscopy and scanning electron microscope and Raman spectra. The electrical and optical properties of a-IGZO thin films are studied. The a-IGZO thin films have LIDT increased from 0.12 J/cm2, 0.16 J/cm2, and 0.23 J/cm2 to 0.24 J/cm2 with absorbance decreased from 22.4%, 18.1%, and 17.3% to 12.3%. The concentrations of oxygen and free carrier (Ne) and thermal conductivity and optical band gap (Eg) and electrical effective mass (m*) are important factors affecting the LIDT of thin films. The thermal conductivity influences the surface temperature and LIDT of thin films. The increased Eg and m* with the decreased Ne in thin films are other important reasons for the increased LIDT. The laser mainly induces thermal damage of thin films with intrinsic processes including avalanche ionization and multi-photon absorption. No apparent phase transformation and lattice expansion exists during laser irradiation for the stable amorphous structures of a-IGZO thin films.

Electronic properties of Ga-In-Zn-O (GIZO) thin films: Effect of post-annealing

Effect of post annealing temperature on electronic properties of Ga-In-Zn-O (GIZO) have quantitatively studied by using reflection electron energy loss spectroscopy (REELS), x-ray photoelectron spectroscopy (XPS), and x-ray absorption fine structure (XAFS) spectra. The band gap values of GIZO are 3.1 eV, 3.5 eV, and 3.8 eV, at room temperature (as deposited), post-annealing at 600 °C, and 700 °C, respectively. The composition of Ga increased and Zn reduced with increasing post-annealing temperature. The formation of Ga-(Ga,Zn) and Zn-(Zn,Ga) bonds in GIZO thin film annealed at 700 °C was confirmed by XAFS study. The electronic properties of GIZO thin films strongly affected by the bonding formation of Zn-O and Ga-O as the effect of annealing temperature.