High-Performance Transparent p-Type Thin-Film Transistor and Circuit with Air-Stable CuI:Cd

Abstract

Advancement of transparent electronics is limited by the lack of stable wide-bandgap p-type semiconductors. Although copper iodide (CuI) shows potential in transparent p-type thin-film transistors (TFTs), controlling carrier concentration and chemical stability remains challenging. Here, it is demonstrated that cadmium (Cd) doping effectively suppresses hole concentration and enhances the air stability of CuI thin films. The incorporation of chemically soft Cd2⁺ ions improve environmental robustness, enabling conventional photolithography under ambient conditions. Optimized 4.0% Cd-doped CuI TFT exhibits a saturation mobility of 5.58 ± 0.71 cm2 V−1 s−1, an Ion/Ioff ratio of 107, and improved negative bias stability (ΔVth = 1.9 V at 2 MV cm−1 for 3600 s). Furthermore, a 7-stage ring oscillator using CuI:Cd film patterned via standard photolithography in air exhibits an operating frequency of 138.38 kHz with a propagation delay of 7.66 µs at a β-ratio of 5:1, highlighting its potential for industrial application of transparent electronics.