Observation of fully recoverable leakage behaviour in HfO2 gate oxide of WS2 2D FETs induced by local mechanical stress

Abstract

A fully recoverable leakage behaviour is observed near the source side of two-dimensional (2D) back gate HfO2 oxide field-effect transistors (FETs) when subjected to a gigapascal -level mechanical stress (MS) applied locally via a nanoindenter tip. Due to the asymmetrical device structure of 2D-FETs, the generated stress is distributed non-uniformly, with maximum compressive stress concentrated near the source ‘S’ terminal rather than the drain ‘D’ terminal. Among the studied channel lengths (L ∼ 0.135 μm to L ∼ 10 μm), longer channels exhibit higher stress near the source terminal than the drain side, attributed to proximity effects under a constant applied load. An increase in gate leakage current with increasing MS is consistently observed, suggesting the generation of shallow traps. At the same time, the apparent reduction in the band gap lower the barrier for electron emission, giving rise to behaviour that appears consistent with a low-voltage dependent Poole–Frenkel mechanism approaching ohmic characteristics. Notably, upon removal of the MS, the gate leakage fully recovers. These findings underscore the mechanical sensitivity of HfO2 gate dielectrics in 2D TMDs semiconductor devices and provide new insights into MS-induced reliability concerns, as well as the potential for mechanically changed electronic responses.