A Study on the Electrical Properties of Atomic Layer Deposition Grown InOx on Flexible Substrates with Respect to N2O Plasma Treatment and the Associated Thin-Film Transistor Behavior under Repetitive Mechanical Stress

Abstract

Indium oxide (InOx) films were deposited at low processing temperature (150 degrees C) by atomic layer deposition (ALD) using [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (InCA-1) as the metal precursor and hydrogen peroxide (H2O2) as the oxidant. As-deposited InOx exhibits a metallic conductor-like behavior owing to a relatively high free-carrier concentration. In order to control the electron density in InOx layers, N2O plasma treatment was carried out on the film surface. The exposure time to N2O plasma was varied (600-2400 s) to evaluate its effect on the electrical properties of InOx. In this regard, thin-film transistors (TFTs) utilizing this material as the active layer were fabricated on polyimide substrates, and transfer curves were measured. As the plasma treatment time increases, the TFTs exhibit a transition from metal-like conductor to a high-performance switching device. This clearly demonstrates that the N2O plasma has an effect of diminishing the carrier concentration in InOx. The combination of low-temperature ALD and N2O plasma process offers the possibility to achieve high-performance devices on polymer substrates. The electrical properties of InOx TFTs were further examined with respect to various radii of curvature and repetitive bending of the substrate. Not only does prolonged cyclic mechanical stress affect the device properties, but the bending direction is also found to be influential. Understanding such behavior of flexible InOx TFTs is anticipated to provide effective ways to design and achieve reliable electronic applications with various form factors.