Abnormal Bias-Temperature Stress and Thermal Instability of $\beta$ -Ga2O3 Nanomembrane Field-Effect Transistor

In this paper, we report on the electrical and thermal instability of β-Ga
₂
O
₃
nanomembrane field-effect transistor with a bottom-gate configuration. The fabricated device exhibits high electrical performance of field-effect mobility of up to 60.9 cm
²
/V·s, on/off-current ratio of 10
⁹
and subthreshold slope of 210 mV/dec. However, we observe abnormal positive threshold voltage (V
_TH
) shifts under negative bias-temperature stress at an elevated operating temperature of 80 °C as well as under temperature-dependent transfer characteristics up to 200 °C. This abnormal instability is significantly influenced by the surface depletion effect, and is discussed using energy band diagram. The opposite VTH shift was achieved by applying atomic-layer deposited Al
₂
O
₃
passivation layer.