Flexible electronics and devices based on oxide semiconductors

Flexible electronics has advanced at a rapid pace in the past dozen years, driving a fascinating transformation of the pattern of consumer electronics. Building integrated photovoltaic and self-powered wearable electronics are two related research fields which promise light weight and high integration devices that do not need external electrical connection. Recent studies have explored the emerging applications of high-voltage thin film transistors (HV-TFTs) and high-voltage thin film diodes (HV-TFDs) in energy management circuits for the above-mentioned applications. We have recently constructed flexible and fully transparent fieldeffect diodes (FEDs) with a high rectification ratio (~5×10⁸) and low leakage current (~10^-15 A/μm). Different from other junction diodes, ours utilize a novel diode- connected TFT architecture, and the field effect plays an important role in the operation. Furthermore, by adopting an offset structure in the FED architecture, the diodes are able to withstand a reverse voltage as high as 150 V; the high AC voltage generated by the triboelectric nanogenerator is rectified into a DC voltage through full-wave rectifier circuits composed of four HVTFDs, then successfully charged into supercapacitors. As building blocks, large-area, low-cost and light weight flexible photodetectors are becoming increasingly important for various flexible device platforms. This new type of detector is not only portable and cost-effective but also readily shaped to fit non-planar surfaces. We developed a fine oxygen-flux controlling technique, and fabricated flexible solar-blind UV and X-ray detectors based on amorphous Ga₂O₃ film sputtered at room temperature. A study of the photoresponse characteristics under UV/X-ray illumination combined with density functional theory calculations indicates that the photocurrent and response decay time strongly depend on the oxygen partial pressure, i.e., oxygen vacancy (V_o) states. Notably, an enhanced X- ray photocurrent is observed and ascribed to the slow-down annihilation rate caused by the neutralization of more ionized Vo states. Flexibility and fatigue tests show no obvious degradation of the device performance under UV and X-ray irradiation, demonstrating the robustness of our photodetectors.