Unique Monotonic Positive Shifts in Threshold Voltages of Ga₂O₃-on-SiC MOSFETs Under Both Unipolar Positive and Negative Bias Stresses

In this study, the instability of heterogeneous Ga2O3-on-SiC (GaOSiC) MOSFETs under unipolar positive/negative bias stress (UPBS/UNBS) was investigated systematically. By adjusting key parameters of stress voltage waveform, including frequency (f), holding time (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{\text {h}}$ </tex-math></inline-formula>), rising time (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{\text {r}}$ </tex-math></inline-formula>), and falling time (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{\text {f}}$ </tex-math></inline-formula>), a two-phase shift in threshold voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula>) with cycle number (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C} _{n}$ </tex-math></inline-formula>) was observed in the UPBS measurement. The UPBS-induced positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula> shift is primarily attributed to electron trapping by traps at/near the Al2O3/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga2O3 interface during the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{\text {r}}$ </tex-math></inline-formula> transient. At the beginning of UPBS test (first phase of degradation), most trap states are unoccupied and the electron trapping is predominant, leading to similar <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula> shifts in different stress conditions. With <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C} _{n}$ </tex-math></inline-formula> further increasing (second phase of degradation), deeper level traps begin trapping electrons due to the accumulation effect, which has been found to have a strong correlation with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{\text {f}}$ </tex-math></inline-formula>. Notably, a monotonic positive shift in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula> was also observed in the UNBS measurement. This <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula> shift under UNBS was modeled using a stretched exponential equation. Parameters of this equation were used to characterize the rate and magnitude of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula> degradation under various stress conditions, elucidating the significant role of f and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${t} _{\text {r}}$ </tex-math></inline-formula> in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula> degradation of GaOSiC MOSFET. TCAD simulations suggest that the monotonic positive shift in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V} _{\text {T}}$ </tex-math></inline-formula> under UNBS is caused by electron trapping at the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga2O3/SiC interfacial layer, which contains a high density of traps.