Flexible Indium Gallium Zinc Oxide Research Articles

Nanowire-Enhanced Fully Transparent and Flexible Indium Gallium Zinc Oxide Transistors with Chitosan Hydrogel Gate Dielectric: A Pathway to Improved Synaptic Properties.

In this study, a transparent and flexible synaptic transistor was fabricated based on a random-network nanowire (NW) channel made of indium gallium zinc oxide. This device employs a biocompatible chitosan-based hydrogel as an electrolytic gate dielectric. The NW structure, with its high surface-to-volume ratio, facilitated a more effective modulation of the channel conductance induced by protonic-ion polarization. A comparative analysis of the synaptic properties of NW- and film-type devices revealed the distinctive features of the NW-type configuration. In particular, the NW-type synaptic transistors exhibited a significantly larger hysteresis window under identical gate-bias conditions. Notably, these transistors demonstrated enhanced paired-pulse facilitation properties, synaptic weight modulation, and transition from short- to long-term memory. The NW-type devices displayed gradual potentiation and depression of the channel conductance and thus achieved a broader dynamic range, improved linearity, and reduced power consumption compared with their film-type counterparts. Remarkably, the NW-type synaptic transistors exhibited impressive recognition accuracy outcomes in Modified National Institute of Standards and Technology pattern-recognition simulations. This characteristic enhances the efficiency of practical artificial intelligence (AI) processes. Consequently, the proposed NW-type synaptic transistor is expected to emerge as a superior candidate for use in high-efficiency artificial neural network systems, thus making it a promising technology for next-generation AI semiconductor applications.

(Invited, Digital Presentation) Oxide TFTs Based on Semiconductors and Semimetals

Oxide semiconductors have opened a new era for large-area, flexible and transparent applications. Despite the progresses, a bottleneck issue of oxide thin-film transistors (TFTs) is the instability either under bias stress or when used as a current source. Furthermore, the carrier mobility and current driving capability need to be improved for high-spec displays. It is still hugely challenging to overcome both issues using the conventional device structure and oxide semiconductor materials.Here, we review our recent work on novel oxide TFTs that show a few desirable properties. Rather than using an ohmic metal contact as the source electrode, a high work-function Schottky source contact enables depletion around the TFT source region, which results in intrinsic immunity to the negative bias illumination stress, no obvious short channel effect, and superb current saturation over a wide range of drain voltage1. The flat saturation current gives rise to an extremely high voltage gain reaching 23,000, which is, to the best of our knowledge, the highest gain ever achieved by a solid-state transistor to date. The threshold voltage is also found to remain stable under different drain voltages, in contrast to standard TFTs, which may be useful in larger-area displays where the drain voltages of the drive TFTs can differ2. Furthermore, the depletion provided by the Schottky source electrode allows utilizing semi-metal ITO to replace IGZO as the TFT channel layer, which significantly enhances the carrier mobility and current driving capability. Other related work may also be discussed in the talk including oxide Schottky diodes operating beyond 10 GHz3, oxide TFTs operating beyond 1 GHz4, significantly enhanced carrier mobility by self-assembled monolayer treatment5,6, and CMOS-like oxide-based logic circuits7,8. References Extremely high-gain source-gated transistors, J Zhang, J Wilson, G Auton, Y Wang, M Xu, Q Xin, A Song, Proceedings of the National Academy of Sciences 116 (11), 4843-4848 (2019)Comparative Study of Short-Channel Effects Between Source-Gated Transistors and Standard Thin-Film Transistors, Zhenze Wang, Li Luo, Yiming Wang, Jiawei Zhang, and Aimin Song, IEEE Transactions on Electron Devices, 69(2), 561 - 566 (2022).Flexible indium–gallium–zinc–oxide Schottky diode operating beyond 2.45 GHz, J Zhang, Y Li, B Zhang, H Wang, Q Xin, A Song, Nature communications 6 (1), 1-7 (2015).Amorphous-InGaZnO thin-film transistors operating beyond 1 GHz achieved by optimizing the channel and gate dimensions, Y Wang, J Yang, H Wang, J Zhang, H Li, G Zhu, Y Shi, Y Li, Q Wang, Qian Xin, Zhongchao Fan, Fuhua Yang, Aimin Song, IEEE Transactions on Electron Devices 65 (4), 1377-1382 (2018).Significant Performance Improvement of Oxide Thin‐Film Transistors by a Self‐Assembled Monolayer Treatment, W Cai, J Zhang, J Wilson, J Brownless, S Park, L Majewski, A Song, Advanced Electronic Materials 6 (5), 1901421 (2020).Significant performance enhancement of very thin InGaZnO thin-film transistors by a self-assembled monolayer treatment, W Cai, J Wilson, J Zhang, J Brownless, X Zhang, LA Majewski, A Song, ACS Applied Electronic Materials 2 (1), 301-308 (2020).Complementary integrated circuits based on p-type SnO and n-type IGZO thin-film transistors, Y Li, J Yang, Y Wang, P Ma, Y Yuan, J Zhang, Z Lin, L Zhou, Q Xin, Aimin Song, IEEE Electron Device Letters 39 (2), 208-211 (2017).Thin Film Sequential Circuits: Flip-Flops and a Counter Based on p-SnO and n-InGaZnO, Y Yuan, J Yang, Y Wang, Z Hu, L Zhou, Q Xin, A Song, IEEE Electron Device Letters 42 (1), 62-65 (2020).

Reliability-Aware SPICE Compatible Compact Modeling of IGZO Inverters on a Flexible Substrate

Accurate circuit simulation reflecting physical and electrical stress is of importance in indium gallium zinc oxide (IGZO)-based flexible electronics. In particular, appropriate modeling of threshold voltage (VT) changes in different bias and bending conditions is required for reliability-aware simulation in both device and circuit levels. Here, we present SPICE compatible compact modeling of IGZO transistors and inverters having an atomic layer deposition (ALD) Al2O3 gate insulator on a polyethylene terephthalate (PET) substrate. Specifically, the modeling was performed to predict the behavior of the circuit using stretched exponential function (SEF) in a bending radius of 10 mm and operating voltages ranging between 4 and 8 V. The simulation results of the IGZO circuits matched well with the measured values in various operating conditions. It is expected that the proposed method can be applied to process improvement or circuit design by predicting the direct current (DC) and alternating current (AC) responses of flexible IGZO circuits.

Healable Cellulose Iontronic Hydrogel Stickers for Sustainable Electronics on Paper

AbstractNovel nature‐based engineered functional materials combined with sustainable and economically efficient processes are among the great challenges for the future of mankind. In this context, this work presents a new generation of versatile flexible and highly conformable regenerated cellulose hydrogel electrolytes with high ionic conductivity and self‐healing ability, capable of being (re)used in electrical and electrochemical devices. They can be provided in the form of stickers and easily applied as gate dielectric onto flexible indium–gallium–zinc oxide transistors, decreasing the manufacturing complexity. Flexible and low‐voltage (<2.5 V) circuits can be handwritten on‐demand on paper transistors for patterning of conductive/resistive lines. This user‐friendly and simplified manufacturing approach holds potential for fast production of low‐cost, portable, disposable/recyclable, and low‐power ion‐controlled electronics on paper, making it attractive for application in sensors and concepts such as the “Internet‐on‐Things.”

Photoactivated high-k lanthanum oxide-aluminum oxide (La2O3–Al2O3) alloy-type gate dielectrics for low-voltage-operating flexible transistors

Low-temperature-processable gate dielectrics with high dielectric constants, low leakage current, and good electrical/mechanical stabilities are largely pursued in diverse electronics including flexible transistors, wearable sensors, integrated logic circuits, and various optoelectronic devices. Here, we report low-temperature photochemically activated gate dielectrics based on a lanthanum oxide-aluminum oxide (La2O3–Al2O3 or LAO) alloy system for a utilization in flexible metal-oxide thin-film transistors (TFTs). With proper alloying of La2O3 and Al2O3 at an optimal ratio, synergetic effects could be achieved from both gate dielectric materials, high dielectric constant and excellent insulating properties. With a La:Al ratio of 2:8, LAO gate dielectrics with high dielectric constant (k = 10.72), low surface roughness (0.517 nm), low leakage current density (1.7 × 10−10 A cm−2 @2 MV cm−1), and high breakdown field (∼4.8 MV cm−1) were achieved. By utilizing the photo-annealed LAO as a gate dielectric, low operating voltage (≤5 V) solution-processed indium-gallium-zinc-oxide (IGZO) TFTs having saturation mobility of 8.5 ± 3.25 cm2 V−1s−1, linear mobility of 10.8 ± 2.03 cm2 V−1s−1, subthreshold slope of 0.228 V dec−1, and on/off ratio of ∼105 are demonstrated. Furthermore, the fabricated IGZO TFTs exhibited negligible hysteresis characteristics (<0.1 V) and good bias stabilities (threshold voltage shift < ±0.1 V). Using an ultrathin (∼2 μm) polyimide film as a substrate, flexible IGZO TFTs successfully operating at a bending radius of 2 mm were realized.

Effect of Simultaneous Mechanical and Electrical Stress on the Electrical Performance of Flexible In-Ga-Zn-O Thin-Film Transistors.

We investigated the effect of simultaneous mechanical and electrical stress on the electrical characteristics of flexible indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). The IGZO TFTs exhibited a threshold voltage shift (∆VTH) under an application of positive-bias-stress (PBS), with a turnaround behavior from the positive ∆VTH to the negative ∆VTH with an increase in the PBS application time, whether a mechanical stress is applied or not. However, the magnitudes of PBS-induced ∆VTH in both the positive and negative directions exhibited significantly larger values when a flexible IGZO TFT was under mechanical-bending stress than when it was at the flat state. The observed phenomena were possibly attributed to the mechanical stress-induced interface trap generation and the enhanced hydrogen diffusion from atomic layer deposition-grown Al2O3 to IGZO under mechanical-bending stress during PBS. The subgap density of states was extracted before and after an application of PBS under both mechanical stress conditions. The obtained results in this study provided potent evidence supporting the mechanism suggested to explain the PBS-induced larger ∆VTHs in both directions under mechanical-bending stress.

Inkjet‐Printed and Deep‐UV‐Annealed YAlOx Dielectrics for High‐Performance IGZO Thin‐Film Transistors on Flexible Substrates

AbstractRecent developments in inkjet printing have proven it a viable method for low‐cost and large‐area coating of oxide materials. The main drawback of this method is the common requirement of a post‐deposition annealing (PDA) of the printed layers at relatively high temperatures (T &gt; 200 °C). This sets a requirement for the substrate to have high glass transition temperature (Tg). To reduce the PDA temperature, deep‐ultraviolet (DUV) annealing is proposed as an effective method. In this study, yttrium aluminum oxide (YAlOx) dielectrics are realized for application in flexible electronic devices via inkjet printing and DUV annealing at a temperature of 150 °C. The effect of the Y concentration on the electrical properties of the dielectrics is investigated. An increase in the Y incorporation is found to increase the dielectric constant and decrease the leakage current of the dielectrics. Flexible indium gallium zinc oxide (IGZO) thin‐film transistors with 50 µm channel widths and 7 µm channel lengths employing printed YAlOx dielectrics are fabricated on polyimide substrates with a maximum processing temperature of 150 °C, yielding a maximum gate leakage current of 10−13A, a high ION/IOFF ratio of 108, and a field effect mobility of 4.3 cm2 V−1 s−1.

Flexible In–Ga–Zn–O Thin-Film Transistors With Sub-300-nm Channel Lengths Defined by Two-Photon Direct Laser Writing

In this paper, the low-temperature (≤150 °C) fabrication and characterization of flexible indium–gallium–zinc–oxide (IGZO) top-gate thin-film transistors (TFTs) with channel lengths down to 280 nm is presented. Such extremely short channel lengths in flexible IGZO TFTs were realized with a novel manufacturing process combining two-photon direct laser writing (DLW) photolithography with Ti/Au/Ti source/drain e-beam evaporation and liftoff. The resulting flexible IGZO TFTs exhibit a saturation field-effect mobility of 1.1 cm $^{\textsf {2}}\cdot \textsf {V}^{-\textsf {1}}\cdot \text {s}^{-\textsf {1}}$ and a threshold voltage of 3 V. Thanks to the short channel lengths (280 nm) and the small gate to source/drain overlap ( $5.2~\mu \text{m}$ ), the TFTs yield a transit frequency of 80 MHz (at 8.5-V gate–source voltage) extracted from the measured S-parameters. Furthermore, the devices are fully functional when wrapped around a cylindrical rod with 6-mm radius, corresponding to 0.4% tensile strain in the TFT channel. These results demonstrate a new methodology to realize entirely flexible nanostructures and prove its suitability for the fabrication of short-channel transistors on polymer substrates for future wearable communication electronics.

Sensing Characteristic of Arrayed Flexible Indium Gallium Zinc Oxide Lactate Biosensor Modified by GO and Magnetic Beads

In this study, the arrayed flexible indium gallium zinc oxide (IGZO) lactate biosensor was modified by graphene oxide (GO) and magnetic beads (MB). The biosensor has arrayed structure with six sensing windows. The arrayed structure with six IGZO windows was fabricated by using radio frequency sputtering system and screen-printed technology. The lactate enzyme was combined with GO and MB, and which was immobilized on the IGZO windows by the crossing-link method. The GO and MB could enhance the average sensitivity of the lactate biosensor, and the optimal content was also investigated. After that, the lactate biosensor was integrated in the microfluidic device, and the average sensitivity also could be enhanced by controlling the flow rate of test solution. Furthermore, the electrochemical reaction of different sensing films could be described by electrochemical impedance spectroscopy.

The Fabrication and Sensing Characteristics of Arrayed Flexible IGZO/Al Urea Biosensor Modified by Graphene Oxide

The urease membrane was immobilized on the surface of indium gallium zinc oxide (IGZO) based on polyethylene terephthalate substrate, which was used to develop an arrayed flexible urea biosensor in this study. In order to improve the properties of arrayed flexible IGZO/Al urea biosensor, graphene oxide (GO) was employed to modify the properties of arrayed flexible IGZO urea biosensor. Compared with the average sensitivity of 1.53 mV/(mg/dl) and linearity of 0.931 for arrayed flexible IGZO/Al urea biosensor, the average sensitivity and linearity of arrayed flexible IGZO urea biosensor modified by GO achieved 3.06 mV/(mg/dl) and 0.970, respectively. As the result, 5 mM pH 7.0 PBS buffer solution was the optimal measurement environment for Urease/IGZO/GO/Al urea biosensor, and which the average sensitivity was 3.65 [mV/(mg/dl)]. Anti-interference testing showed the arrayed flexible IGZO/Al urea biosensor modified by GO was not easily interfered from the other materials.

Sensing Characteristic of Arrayed Flexible Indium Gallium Zinc Oxide Lactate Biosensor Modified by Magnetic Beads

In this paper, we proposed an arrayed flexible lactate biosensor, and indium gallium zinc oxide (IGZO) was used as the sensing film. The screen-printed technology was used to miniaturize the reference electrode and conductive wires. Lactate dehydrogenase and nicotinamide adenine dinucleotide were used to deposit enzyme membrane on IGZO sensing film to catalyze lactate. In the measurement, the arrayed flexible IGZO lactate biosensor was immersed in the lactate solutions, which concentrations were 0.2, 0.7, 1.3, 2, and 3 mM, respectively. The average sensitivity and linearity of lactate biosensor were 114.900 mV/decade and 0.948, respectively.

Flexible Quasi-Vertical In-Ga-Zn-O Thin-Film Transistor With 300-nm Channel Length

In this letter, we report a flexible Indium–Gallium–Zinc-Oxide quasi-vertical thin-film transistor (QVTFT) with 300-nm channel length, fabricated on a free-standing polyimide foil, using a low-temperature process $10^{4}$ , a threshold voltage of 1.5 V, a maximum transconductance of 0.73 $\mu \text{S}~\mu {\rm m}^{-1}$ , and a total gate capacitance of 76 nF $\mu {\rm m}^{-1}$ . From S-parameter measurements, we extracted a transit frequency of 1.5 MHz. Furthermore, the flexible QVTFT is fully operational when bent to a tensile radius of 5 mm.