Optimization of solution-processed amorphous cadmium gallium oxide for high-performance thin-film transistors

Abstract

Metal oxide semiconductors have several advantages over conventional Si-based materials, including high mobility even in the amorphous state, excellent optical transparency, and compatibility with low-cost fabrication processes. Despite the toxic nature of cadmium compounds, the excellent electrical and optical properties of CdO have attracted research attention for potential applications in high-performance military and aerospace technologies. In this study, an amorphous cadmium gallium oxide (a-CdGaO)-based thin-film transistor (TFT) (optimized at Cd : Ga ratio of 5.5 : 4.5) is demonstrated, with a maximum mobility of 17.68 (14.10 in average) cm² V⁻¹ s⁻¹, an on/off current ratio (I_on/I_off) of 1.01 × 10⁹, a threshold voltage (V_th) of 0.73 V, optical transmittance (T₅₅₀) > 90%, a bias stability of 4.36 V under positive bias stress (PBS), a bias stability of −1.83 V under negative bias stress (NBS), and a high frequency of 250 kHz when applied on a seven-stage oscillator ring circuit. Additionally, the optimized a-Cd_5.5Ga_4.5O_12.25 device showed excellent stability over time with negligible change of mobility and V_th values after one week exposure to ambient air condition.