Ultra-Low Voltage Metal Oxide Thin Film Transistor by Low-Temperature Annealed Solution Processed LiAlO2 Gate Dielectric

Abstract

Abstract: Low surface-roughness and high-capacitance ion-conducting LiAlO2 gate dielectric thin film has been fabricated by sol–gel technique to develop ultra-low voltage (≤ 1.0 V) indium-zinc-oxide thin film transistor (TFT). This LiAlO2 dielectric shows α-LiAlO2 and γ-LiAlO2 phases those have been fabricated at two different temperatures. For both phases, mobile Li-ion is responsible to achieve a high dielectric constant (κ) of the material that helps to reduce the operating voltage of TFT. Additionally, lower surface roughness of LiAlO2 thin film creates a low-density trap state in the semiconductor/dielectric interface which is capable to reduce operating voltage within 1.0-volt. The device with 700 °C annealed γ-LiAlO2 gate dielectric shows the best device performance with an electron mobility of 25 cm2 V−1 s−1 and an on/off ratio of 3 × 105. Instead, 350 °C annealed α-LiAlO2 dielectric require only one volt to saturate the drain current and shows its mobility and on/off ratio are 13.5 cm2 V−1 s−1 and 1 × 104 respectively. Such kind of unusually low operation voltage TFT fabrication becomes possible because of the higher Li+ mobility of α-LiAlO2 gate dielectric and very low surface trap density. A model on carrier transport mechanism has been prepossessed to explain this achievement. Graphic abstract: [Figure not available: see fulltext.]. © 2019, The Korean Institute of Metals and Materials.