Design of an Atomic Layer-Deposited In2O3/Ga2O3 Channel Structure for High-Performance Thin-Film Transistors

Abstract

For potential application in advanced memory devices such as dynamic random-access memory (DRAM) or NAND flash, nanolaminated indium oxide (In–O) and gallium oxide (Ga–O) films with five different vertical cation distributions were grown and investigated by using a plasma-enhanced atomic layer deposition (PEALD) process. Specifically, this study provides an in-depth examination of how the control of individual layer thicknesses in the nanolaminated (NL) IGO structure impacts not only the physical and chemical properties of the thin film but also the overall device performance. To eliminate the influence of the cation composition ratio and overall thickness on the IGO thin film, these parameters were held constant across all conditions. Thin-film transistors (TFTs) with a homogeneous In_0.72Ga_0.29O_x channel layer (referred to as IGO18) exhibited a reasonable field-effect mobility (μ_FE) of 58.1 cm²/(V s) and I_ON/OFF ratio of >10⁸. A significant improvement (∼94.1 cm²/(V s)) in μ_FE was observed for TFTs with an In₂O₃/Ga₂O₃ heterojunction stack (referred to as IGO1). Because the channel layers of both devices had an identical average cation composition and physical thickness, the superior performance of the latter can be attributed to the emergence of a quasi-two-dimensional electron gas (2DEG) and the attainment of high-quality crystallinity. This study underscores the criticality of supercycle duty design to prevent cation intermixing, enabling the exploitation of the 2DEG effect in high-performance oxide TFTs for memory device applications.