Thermopower Modulation Analyses of High-Mobility Transparent Amorphous Oxide Semiconductor Thin-Film Transistors

Abstract

Transparent amorphous oxide semiconductor InSnZnO x (ITZO)-based thin-film transistors (TFTs) exhibit a high field-effect mobility (μFE). Although ITZO-TFTs have attracted increasing attention as a next-generation backplane of flat panel displays, the origin of the high μFE remains unclear due to the lack of systematic quantitative analyses using thermopower (S) as the measure. Here, we show that the high μFE originates from an extremely light carrier effective mass (m*) and a long carrier relaxation time (τ). The S measurements of several ITZO films with different carrier concentrations clarified that m* of ITZO films is ∼0.11 m 0, which is ∼70% of that of a commercial oxide semiconductor, amorphous InGaZnO4 (∼0.16 m 0). We then fabricated bottom-gate-top-contact ITZO-TFTs displaying excellent transistor characteristics (μFE ∼ 58 cm2 V–1 s–1) using amorphous AlO x as the gate insulator and demonstrated that the effective thickness increases with the gate voltage. This suggests that the bulk predominantly contributes to the drain current, which results in τ as long as ∼3.6 fs, which is quadruple that of amorphous InGaZnO4-TFTs (∼0.9 fs). The present results are useful to further improve the mobility of ITZO-TFTs.

High-mobility and high-reliability Zn-incorporated amorphous In2O3-based thin-film transistors

“…S reflects the energy differential of the density of states at the Fermi energy, providing an estimate of carrier effective mass (m*) of materials. [28][29][30] m* is inversely proportional to the mobility (μ = e•τ•m* −1 , where e and τ are the electron charge and carrier relaxation time, respectively). Figure 4(a) shows the S values of the IZO films as a function of n (log scale) at room temperature.…”

Improved Electron Transport Properties of Zn-Rich In–Ga–Zn–O Thin-Film Transistors

“…Thermopower modulation analyses of the IGZO m -TFTs were performed at room temperature in air. Details of the thermopower modulation analyses are published elsewhere (SrTiO 3 -TFTs, InGaZnO 4 -TFTs, BaSnO 3 -TFTs, SnO 2 -TFTs, InSnZnO x -TFTs, and GaN-TFTs).…”