Electron mobility enhancement in solution-processed low-voltage In₂O₃ transistors via channel interface planarization

The quality of the gate dielectric/semiconductor interface in thin-film transistors (TFTs) is known to determine the optimum operating characteristics attainable. As a result in recent years the development of methodologies that aim to improve the channel interface quality has become a priority. Herein, we study the impact of the surface morphology of three solution-processed high-k metal oxide dielectrics, namely AlO_x, HfO_x, and ZrO_x, on the operating characteristics of In₂O₃ TFTs. Six different dielectric configurations were produced via single or double-step spin-casting of the various precursor formulations. All layers exhibited high areal capacitance in the range of 200 to 575 nF/cm², hence proving suitable, for application in low-voltage n-channel In₂O₃ TFTs. Study of the surface topography of the various layers indicates that double spin-cast dielectrics exhibit consistently smoother layer surfaces and yield TFTs with improved operating characteristics manifested, primarily, as an increase in the electron mobility (μ). To this end, μ is found to increase from 1 to 2 cm²/Vs for AlO_x, 1.8 to 6.4 cm²/Vs for HfO_x, and 2.8 to 18.7 cm²/Vs for ZrO_x-based In₂O₃ TFTs utilizing single and double-layer dielectric, respectively. The proposed method is simple and potentially applicable to other metal oxide dielectrics and semiconductors.