Passivation layer effect on the positive bias temperature instability of molybdenum disulfide thin film transistors

Abstract

As two-dimensional (2D) materials have a large surface to volume ratio, the stability of thin film transistors (TFTs) is likely to be lowered with air exposure. Therefore, we study the positive bias temperature instability (PBTI) of chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) TFTs before and after deposition of a passivation layer. The results of the PBTI study demonstrate that the fabricated devices adjust to the stretched-exponential model, which shows a threshold voltage shift attributed to the charge trapping mechanism. However, by depositing the passivation layer (Al2O3) that physically blocks the charge transfer process with O2 and H2O adsorbed to the surface of the MoS2 channel, the threshold voltage shifted reduces from 10 V to 7.4 V under stress condition. The quantitative value of tau (τ), one of the fitting parameters of the stretched-exponential model, also decreases from 6453 s to 5153 s, resulting in improved device stability.