High mobility polycrystalline indium oxide thin-film transistors by means of plasma-enhanced atomic layer deposition

Abstract

Indium oxide thin films are deposited via plasma-enhanced atomic layer deposition (PEALD) to exploit their potential as a semiconductor in high mobility thin-film transistors (TFTs), which are suitable for fast driving applications such as high resolution displays. The films are successfully grown by the reaction between an Et₂InN(SiMe₃)₂ liquid precursor and oxygen plasma at temperatures ranging from 100 °C to 250 °C giving a saturated growth rate value of ∼1.45 Å per cycle at the ALD window with precisely controlled thickness and uniformity. The plasma reaction enhances the film growth rate and changes the electrical properties of the films. Depending on the substrate temperatures, each film has a different chemical composition, thereby showing different electrical characteristics. Indium oxide films grown by PEALD show a lower carrier density of ∼4 × 10¹⁹ cm⁻³ than those prepared by thermal ALD due to the reactive oxygen plasma source in the former. Offering the precise control of thickness and high quality of indium oxide grown by PEALD, and with a proper post thermal-annealing and passivation process, the possibility of exploiting the potential of semiconductor characteristics of indium oxide is verified from bottom-gate coplanar structured TFTs, which exhibit a high mobility as high as 39.2 cm² V⁻¹ s⁻¹, a turn-on voltage value of −1.18 V, and a sub-threshold voltage of 0.27 V dec⁻¹ in a linear region. On the basis of this outstanding performance, the PEALD-InO_x TFTs developed in this study would be suitable for diverse microelectronic devices.