Electric field thermopower modulation analyses of the operation mechanism of transparent amorphous SnO2 thin-film transistor

Abstract

Transparent amorphous oxide semiconductors (TAOSs) based transparent thin-film transistors (TTFTs) with high field effect mobility (μ_FE) are essential for developing advanced flat panel displays. Among TAOSs, amorphous (a-) SnO₂ has several advantages against current a-InGaZnO₄ such as higher μ_FE and being indium-free. Although a-SnO₂ TTFT has been demonstrated several times, the operation mechanism has not been clarified thus far due to the strong gas sensing characteristics of SnO₂. Here we clarify the operation mechanism of a-SnO₂ TTFT by electric field thermopower modulation analyses. We prepared a bottom-gate top-contact type TTFT using 4.2-nm-thick a-SnO₂ as the channel without any surface passivation. The effective thickness of the conducting channel was ∼1.7 ± 0.4 nm in air and in vacuum, but a large threshold gate voltage shift occurred in different atmospheres; this is attributed to carrier depletion near at the top surface (∼2.5 nm) of the a-SnO₂ due to its interaction with the gas molecules and the resulting shift in the Fermi energy. The present results would provide a fundamental design concept to develop a-SnO₂ TTFT.