Light response behaviors of amorphous In–Ga–Zn–O thin-film transistors via in situ interfacial hydrogen doping modulation

Unlocking Neuromorphic Vision: Advancements in IGZO-Based Optoelectronic Memristors with Visible Range Sensitivity

Optoelectronic memristors based on amorphous oxide semiconductors (AOSs) are promising devices for the development of spiking neural network (SNN) hardware in neuromorphic vision sensors. In such devices, the conductance state can be controlled by both optical and electrical stimuli, while the typical persistent photoconductivity (PPC) of AOS materials can be used to emulate synaptic functions. However, due to the large band gap of these materials, sensitivity to visible light (red/green/blue) is difficult to accomplish, which hinders applications requiring color discrimination. In this work, we report a 4 μm2 hydrogen-doped (H-doped) indium-gallium-zinc oxide (IGZO) optoelectronic memristor that emulates all of the important rules of SNNs such as short- to long-term memory transition (STM-LTM), paired-pulse facilitation (PPF), spike-time-dependent plasticity (STDP), and learning and forgetting capabilities. By the incorporation of hydrogen gas in the sputtering deposition of IGZO, visible sensitivity was achieved for green and blue wavelengths. Additionally, extremely high light/dark ratios of 179, 93, and 12 are demonstrated for wavelengths of 365, 405, and 505 nm, respectively, due to hydrogen-induced subgap states and device miniaturization. Therefore, the proposed device shows remarkable potential for integration with the pixel circuits of IGZO-based displays with extreme resolution for a true intelligent self-processing display.

Amorphous InGaZnO Thin-Film Transistors with Double-Stacked Channel Layers for Ultraviolet Light Detection

Amorphous InGaZnO thin film transistors (a-IGZO TFTs) with double-stacked channel layers (DSCL) were quite fit for ultraviolet (UV) light detection, where the best DSCL was prepared by the depositions of oxygen-rich (OR) IGZO followed by the oxygen-deficient (OD) IGZO films. We investigated the influences of oxygen partial pressure (P_O) for DSCL-TFTs on their sensing abilities by experiments as well as Technology Computer Aided Design (TCAD) simulations. With the increase in P_O values for the DSCL depositions, the sensing parameters, including photogenerated current (I_photo), sensitivity (S), responsivity (R), and detectivity (D*) of the corresponding TFTs, apparently degraded. Compared with P_O variations for the OR-IGZO films, those for the OD-IGZO depositions more strongly influenced the sensing performances of the DSCL-TFT UV light detectors. The TCAD simulations showed that the variations of the electron concentrations (or oxygen vacancy (V_O) density) with P_O values under UV light illuminations might account for these experimental results. Finally, some design guidelines for DSCL-TFT UV light detectors were proposed, which might benefit the potential applications of these novel semiconductor devices.

Polyimide-Doped Indium-Gallium-Zinc Oxide-Based Transparent and Flexible Phototransistor for Visible Light Detection

We report a transparent and flexible polyimide (PI)-doped single-layer (PSL) phototransistor for the detection of visible light. The PSL was deposited on a SiO₂ gate insulator by a co-sputtering process using amorphous indium-gallium-zinc oxide (IGZO) and PI targets simultaneously. The PSL acted as both a channel layer and a visible-light absorption layer. PI is one of the few flexible organic materials that can be fabricated into sputtering targets. Compared with the IGZO phototransistor without PI doping, the PSL phototransistor exhibited improved optoelectronic characteristics under illumination with 635 nm red light of 1 mW/mm² intensity; the obtained photoresponsivity ranged from 15.00 to 575.00 A/W, the photosensitivity from 1.38 × 10¹ to 9.86 × 10⁶, and the specific detectivity from 1.35 × 10⁷ to 5.83 × 10¹¹ Jones. These improvements are attributed to subgap states induced by the PI doping, which formed decomposed organic molecules, oxygen vacancies, and metal hydroxides. Furthermore, a flexible PSL phototransistor was fabricated and showed stable optoelectronic characteristics even after 10,000 bending tests.

Improving Device Characteristics of Dual-Gate IGZO Thin-Film Transistors with Ar-O2 Mixed Plasma Treatment and Rapid Thermal Annealing

In this study, high-performance indium-gallium-zinc oxide thin-film transistors (IGZO TFTs) with a dual-gate (DG) structure were manufactured using plasma treatment and rapid thermal annealing (RTA). Atomic force microscopy measurements showed that the surface roughness decreased upon increasing the O2 ratio from 16% to 33% in the argon-oxygen plasma treatment mixture. Hall measurement results showed that both the thin-film resistivity and carrier Hall mobility of the Ar-O2 plasma-treated IGZO thin films increased with the reduction of the carrier concentration caused by the decrease in the oxygen vacancy density; this was also verified using X-ray photoelectron spectroscopy measurements. IGZO thin films treated with Ar-O2 plasma were used as channel layers for fabricating DG TFT devices. These DG IGZO TFT devices were subjected to RTA at 100 °C-300 °C for improving the device characteristics; the field-effect mobility, subthreshold swing, and ION/IOFF current ratio of the 33% O2 plasma-treated DG TFT devices improved to 58.8 cm2/V·s, 0.12 V/decade, and 5.46 × 108, respectively. Long-term device stability reliability tests of the DG IGZO TFTs revealed that the threshold voltage was highly stable.

A Review of Phototransistors Using Metal Oxide Semiconductors: Research Progress and Future Directions

Metal oxide thin-film transistors have been continuously researched and mass-produced in the display industry. However, their phototransistors are still in their infancy. In particular, utilizing metal oxide semiconductors as phototransistors is difficult because of the limited light absorption wavelength range and persistent photocurrent (PPC) phenomenon. Numerous studies have attempted to improve the detectable light wavelength range and the PPC phenomenon. Here, recent studies on metal oxide phototransistors are reviewed, which have improved the range of light wavelengths and the PPC phenomenon by introducing an absorption layer of oxide or non-oxide hybrid structure. The materials of the absorption layer applied to absorb long-wavelength light are classified into oxides, chalcogenides, organic materials, perovskites, and nanodots. Finally, next-generation convergence studies combined with other research fields are introduced and future research directions are detailed.