Modulating Cationic Ratios for High-Performance Transparent Solution-Processed Electronics

Liquid-metal based flexible a-IZTO ultrathin films for electrical and optical applications

Amorphous indium zinc tin oxide (a-IZTO) is a kind of transparent conductive oxide (TCO), which can be used in transparent electrodes, transistors, and flexible devices. At present, a key limitation of a-IZTO is the costly vacuum manufacturing technology, and its commercial production is also restricted by the complex raw material preparation process. In this article, we report a liquid metal-based van der Waals (vdW) exfoliation technique by which a-IZTO films with several nanometres thickness are fabricated. The a-IZTO films fabricated in ambient air have a size on the centimeter scale and an optical transmittance of 99.64%; they are also large-area flexible oxide films. In order to illustrate the capabilities of this technology, we fabricated thin film transistors (TFTs) and photodetectors based on a-IZTO films. An a-IZTO thin film transistor (TFT) has an on/off ratio of 10⁶. When the V_ds is 5 V, the responsivity, detectivity and external quantum efficiency of an a-IZTO photodetector are 7.57 × 10⁴ A W^-1, 4.00 × 10¹⁵ Jones and 3.68 × 10⁵%, respectively, exhibiting one of the top performances in this field.

Ultralow-Thermal-Budget-Driven IWO-Based Thin-Film Transistors and Application Explorations

Exploiting multifunctional thin film transistors (TFTs) by low-temperature manufacturing strategy is a crucial step toward flexible electronics. Herein, a multifunctional indium-tungsten-oxide (IWO)-based TFT, gated by solid-state chitosan electrolyte membrane, is fabricated on paper substrate at room temperature. The chitosan exhibits a high specific electric-double-layer capacitance of 2.0 µF cm^-2 due to the existence of mobile protons. The IWO-based TFT possesses excellent electrical properties, including a low threshold voltage of 0.2 V, larger current switching ratio of 1.3 × 10⁶, high field effect mobility of 15.0 cm² V^-1s^-1, and small subthreshold swing of 117 mV/decade, respectively. Multifunctional operations including inverter, Schmitt triggers, and NAND gate are successfully demonstrated. As an example of information processing, the essential signal transmission functions of biological synapses also be emulated in the fabricated IWO-based TFTs. The experimental results indicate that such flexible IWO-based TFTs on low-cost and biodegradable paper provide the new-concept building blocks for flexible electronics.

Highly Reliable Implementation of Optimized Multicomponent Oxide Systems Enabled by Machine Learning-Based Synthetic Protocol

Multicomponent oxide systems are one of the essential building blocks in a broad range of electronic devices. However, due to the complex physical correlation between the cation components and their relations with the system, finding an optimal combination for desired physical and/or chemical properties requires an exhaustive experimental procedure. Here, a machine learning (ML)-based synthetic approach is proposed to explore the optimal combination conditions in a ternary cationic compound indium-zinc-tin oxide (IZTO) semiconductor exhibiting high carrier mobility. In particular, by using support vector regression algorithm with radial basis function kernel, highly accurate mobility prediction can be achieved for multicomponent IZTO semiconductor with a sufficiently small number of train datasets (15-20 data points). With a synergetic combination of solution-based synthetic route for IZTO fabrication enabling a facile control of the composition ratio and tailored ML process for multicomponent system, the prediction of high-performance IZTO thin-film transistors is possible with expected field-effect mobility as high as 13.06 cm² V^-1 s^-1 at the In:Zn:Sn ratio of 63:27:10. The ML prediction is successfully translated into the empirical analysis with high accuracy, validating the protocol is reliable and a promising approach to accelerate the optimization process for multicomponent oxide systems.

Performance Improvement of ZnSnO Thin-Film Transistors with Low-Temperature Self-Combustion Reaction

Conventional sol-gel solutions have received significant attention in thin-film transistor (TFT) manufacturing because of their advantages such as simple processing, large-scale applicability, and low cost. However, conventional sol-gel processed zinc tin oxide (ZTO) TFTs have a thermal limitation in that they require high annealing temperatures of more than 500 °C, which are incompatible with most flexible plastic substrates. In this study, to overcome the thermal limitation of conventional sol-gel processed ZTO TFTs, we demonstrated a ZTO TFT that was fabricated at low annealing temperatures of 350 °C using self-combustion. The optimized device exhibited satisfactory performance, with μsat of 4.72 cm2/V∙s, Vth of −1.28 V, SS of 0.86 V/decade, and ION/OFF of 1.70 × 106 at a low annealing temperature of 350 °C for one hour. To compare a conventional sol-gel processed ZTO TFT with the optimized device, thermogravimetric and differential thermal analyses (TG-DTA) and X-ray photoelectron spectroscopy (XPS) were implemented.

Printed gas sensors

This review presents the recent development of printed gas sensors based on functional inks.

Field-Driven Athermal Activation of Amorphous Metal Oxide Semiconductors for Flexible Programmable Logic Circuits and Neuromorphic Electronics

Despite extensive research, large-scale realization of metal-oxide electronics is still impeded by high-temperature fabrication, incompatible with flexible substrates. Ideally, an athermal treatment modifying the electronic structure of amorphous metal oxide semiconductors (AMOS) to generate sufficient carrier concentration would help mitigate such high-temperature requirements, enabling realization of high-performance electronics on flexible substrates. Here, a novel field-driven athermal activation of AMOS channels is demonstrated via an electrolyte-gating approach. Facilitating migration of charged oxygen species across the semiconductor-dielectric interface, this approach modulates the local electronic structure of the channel, generating sufficient carriers for charge transport and activating oxygen-compensated thin films. The thin-film transistors (TFTs) investigated here depict an enhancement of linear mobility from 51 to 105.25 cm² V^-1 s^-1 (ionic-gated) and from 8.09 to 14.49 cm² V^-1 s^-1 (back-gated), by creating additional oxygen vacancies. The accompanying stochiometric transformations, monitored via spectroscopic measurements (X-ray photoelectron spectroscopy) corroborate the detailed electrical (TFT, current evolution) parameter analyses, providing critical insights into the underlying oxygen-vacancy generation mechanism and clearly demonstrating field-induced activation as a promising alternative to conventional high-temperature annealing strategies. Facilitating on-demand active programing of the operation modes of transistors (enhancement vs depletion), this technique paves way for facile fabrication of logic circuits and neuromorphic transistors for bioinspired computing.

Flexible Ionic-Electronic Hybrid Oxide Synaptic TFTs with Programmable Dynamic Plasticity for Brain-Inspired Neuromorphic Computing

Emulation of biological synapses is necessary for future brain-inspired neuromorphic computational systems that could look beyond the standard von Neuman architecture. Here, artificial synapses based on ionic-electronic hybrid oxide-based transistors on rigid and flexible substrates are demonstrated. The flexible transistors reported here depict a high field-effect mobility of ≈9 cm² V^-1 s^-1 with good mechanical performance. Comprehensive learning abilities/synaptic rules like paired-pulse facilitation, excitatory and inhibitory postsynaptic currents, spike-time-dependent plasticity, consolidation, superlinear amplification, and dynamic logic are successfully established depicting concurrent processing and memory functionalities with spatiotemporal correlation. The results present a fully solution processable approach to fabricate artificial synapses for next-generation transparent neural circuits.

Synergistic effects of water addition and step heating on the formation of solution-processed zinc tin oxide thin films: towards high-mobility polycrystalline transistors

Thin-film transistors (TFTs) with high mobility and good uniformity are attractive for next-generation flat panel displays. In this work, solution-processed polycrystalline zinc tin oxide (ZTO) thin film with well-ordered microstructure is prepared, thanks to the synergistic effect of water addition and step heating. The step heating treatment other than direct annealing induces crystallization, while adequate water added to precursor solution further facilitates alloying and densification process. The optimal polycrystalline ZTO film is free of hierarchical sublayers, and featured with an increased amount of ternary phases, as well as a decreased fraction of oxygen vacancies and hydroxides. TFT devices based on such an active layer exhibit a remarkable field-effect mobility of 52.5 cm² V^-1 s^-1, a current on/off ratio of 2 × 10⁵, a threshold voltage of 2.32 V, and a subthreshold swing of 0.36 V dec^-1. Our work offers a facile method towards high-performance solution-processed polycrystalline metal oxide TFTs.