Wearable 1 V operating thin-film transistors with solution-processed metal-oxide semiconductor and dielectric films fabricated by deep ultra-violet photo annealing at low temperature

Abstract

Amorphous metal-oxide semiconductors (AOSs) such as indium-gallium-zinc-oxide (IGZO) as an active channel have attracted substantial interests with regard to high-performance thin-film transistors (TFTs). Recently, intensive and extensive studies of flexible and/or wearable AOS-based TFTs fabricated by solution-process have been reported for emerging approaches based on device configuration and fabrication process. However, several challenges pertaining to practical and effective solution-process technologies remain to be resolved before low-power consuming AOS-based TFTs for wearable electronics can be realized. In this paper, we investigate the non-thermal annealing processes for sol-gel based metal-oxide semiconductor and dielectric films fabricated by deep ultraviolet (DUV) photo and microwave annealing at low temperature, compared to the conventional thermal annealing at high temperature. A comprehensive investigation including a comparative analysis of the effects of DUV photo and microwave annealing on the degree of metal-oxide-metal networks in amorphous IGZO and high-dielectric-constant (high-k) aluminum oxide (Al₂O₃) films and device performance of IGZO-TFTs in a comparison with conventional thermal annealing at 400 °C was conducted. We also demonstrate the feasibility of wearable IGZO-TFTs with Al₂O₃ dielectrics on solution-processed polyimide films exhibiting a high on/off current ratio of 5 × 10⁴ and field effect mobility up to 1.5 cm²/V-s operating at 1 V. In order to reduce the health risk and power consumption during the operation of wearable electronics, the operating voltage of IGZO-TFTs fabricated by non-thermal annealing at low temperature was set below ~1 V. The mechanical stability of wearable IGZO-TFTs fabricated by an all-solution-process except metal electrodes, against cyclic bending tests with diverse radius of curvatures in real-time was investigated. Highly stable and robust flexible IGZO-TFTs without passivation films were achieved even under continuous flexing with a curvature radius of 12 mm.