High performance top-gated indium–zinc–oxide thin film transistors with in-situ formed HfO2 gate insulator

Abstract

We report on top-gated indium–zinc–oxide (IZO) thin film transistors (TFTs) with an in-situ formed HfO2 gate dielectric insulator. Building on our previous demonstration of high-performance IZO TFTs with Al2O3/HfO2 gate dielectric, we now report on a one-step process, in which Hf is evaporated onto the 20nm thick IZO channel, forming a partially oxidized HfOx layer, without any additional insulator in-between. After annealing in air at 300°C, the in-situ reaction between partially oxidized Hf and IZO forms a high quality HfO2 gate insulator with a low interface trapped charge density NTC~2.3×1011cm−2 and acceptably low gate leakage <3×10−7A/cm2 at gate voltage VG=1V. The annealed TFTs with gate length LG=50μm have high mobility ~95cm2/V∙s (determined via the Y-function technique), high on/off ratio~107, near-zero threshold voltage VT=−0.02V, and a subthreshold swing of 0.062V/decade, near the theoretical limit. The on-current of our proof-of-concept TFTs is relatively low, but can be improved by reducing LG, indicating that high-performance top-gated HfO2-isolated IZO TFTs can be fabricated using a single-step in-situ dielectric formation approach.