High-Performance 1-V ZnO Thin-Film Transistors With Ultrathin, ALD-Processed ZrO2Gate Dielectric

Abstract

The high-performance ZnO thin-film transistors (TFTs) were fabricated on indium tin oxide glass with high-capacitance atomic layer deposition (ALD)-processed ZrO2 as the gate dielectric. The 5-nm ultrathin ZrO2 film showed a very high areal capacitance of 820 nF/cm2 at 20 Hz, a relatively high breakdown field of 14 MV/cm, and low surface root-mean-square (rms) roughness of 0.22 nm, making it possible for ZnO/ZrO2 TFT to not only be operated by an ultralow operating voltage of 1 V but also present a near theoretical limit subthreshold swing of 69 mV/dec. Furthermore, the ZnO TFT with a 5-nm ZrO2 gate dielectric exhibited excellent performance, such as a high Ion/Ioff of 107, large field effect mobility of 36.8 cm2/Vs, low-density of trapping states ( ${N}_{{\text {trap}}}$ ) of $1.6\times 10^{{11}}$ eV−1cm−2, and negligible hysteresis. In addition, the electron transport mode was built to explain the high mobility of nanocrystalline ZnO TFT. As a result, the ultralow operating voltage TFTs exhibited great potential for low-powered electronics applications.