High-Performance 1-V ZnO Thin-Film Transistors With Ultrathin, ALD-Processed ZrO₂ Gate Dielectric

The high-performance ZnO thin-film transistors (TFTs) were fabricated on indium tin oxide glass with high-capacitance atomic layer deposition (ALD)-processed ZrO ₂ as the gate dielectric. The 5-nm ultrathin ZrO ₂ film showed a very high areal capacitance of 820 nF/cm ² 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/ZrO ₂ 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 ZrO ₂ gate dielectric exhibited excellent performance, such as a high I _on /I _off of 10 ⁷ , large field effect mobility of 36.8 cm ² /Vs, low-density of trapping states ( ${N}_{{\text {trap}}}$ ) of $1.6\times 10^{{11}}$ eV ⁻¹ cm ⁻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.