Negative constant voltage stress-induced threshold voltage instability in hydrogen-terminated diamond MOSFETs with low-temperature deposited Al2O3

Threshold voltage analysis can help reveal the reliability of semiconductor transistors and its underlying mechanism. Herein, negative constant voltage stress (NCVS)-induced threshold voltage instability is studied in hydrogen-terminated diamond metal-oxide-semiconductor field-effect transistors (HD MOSFETs) with an Al2O3 dielectric layer deposited via atomic layer deposition at 90 °C. An unusual bidirectional shift in threshold voltage (Vth) can be observed with time. When a weak gate NCVS is applied, Vth gradually decreases during the first 500 s but increases in the next 500 s. A similar but opposite phenomenon is observed when the HD MOSFETs are in a recovery stage upon removing the NCVS, i.e., Vth increases in the first 500 s but decreases in the next 4500 s. A kinetic hydrogen motion model shows that this phenomenon can be attributed to the larger characteristic time constant of the unactuated oxygen-dangling bonds (UODBs) compared to that of the traps in the gate dielectric. Consequently, the trapping effect dominates and decreases Vth at the onset of NCVS. After 500 s, the UODB effects can be observed, increasing Vth. In the recovery stage, Vth is larger than the initial value. Further, modified hydrogen kinetic equations accounting for the dynamic effects of UODBs and traps are provided to quantitatively analyze the results.