59.9 mV·dec Subthreshold Swing Achieved in Zinc Tin Oxide TFTs with in Situ Atomic Layer Deposited AlO Gate Insulator

Abstract

Here, by depositing both the zinc tin oxide (ZTO) channel and Al2O3 gate dielectric layer using atomic layer deposition (ALD) without breaking vacuum, we made TFTswith a steep subthreshold swing (SS) of 59.9mV dec-1, near the room temperature Boltzmann limit. An extremely low interface trap density of 9.59×109cm-2eV-1 was extracted from the measured SS value, and was corroborated by the high-low frequency capacitance method. Comparison with other TFT processes shows that both the higher-k gate dielectric and the in situ ALD process are required to obtain the low SS value. The device made with in situ dielectric deposition exhibits a maximum linear mobility of 19.2 cm2V-1s-1, an ON/OFF current ratio > 108, and a threshold voltage of 1.3 V. The sharp SS achieved here will enable low voltage electronics using this scalable ALD technology.