In–Ga ratio-dependent positive bias stress stability in InGaO based thin-film transistors

In this Letter, we investigated positive bias stress (PBS) stability in InGaO based thin-film transistors considering the effect of elementary ratios between indium and gallium. Different from the widely observed trade-off between negative bias stress stability and mobility, a high In–Ga ratio brings both higher mobility and PBS stability. By increasing the In–Ga ratio from 3:1 to 7:1, the mobility was improved from 16 to 30 cm2V−1s−1. Simultaneously, the shift of VTH at continuous gate bias VStress = 4 V for 1500 s was suppressed from 0.8 to 0.33 V. The higher PBS stability in larger In:Ga ratio samples was attributed to the larger energetic offset between the transport band, i.e., EC in InGaO, and the typical defect band ET in SiOX dielectric, which effectively weakens the charge trapping process from the channel to the insulator layer. The assumption was supported by further photoemission characterizations, which showed a clear dependence of energetic position of EC on the In–Ga ratio.