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 degrees C. An unusual bidirectional shift in threshold voltage (V-th) can be observed with time. When a weak gate NCVS is applied, V-th 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., V-th 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 V-th at the onset of NCVS. After 500 s, the UODB effects can be observed, increasing V-th. In the recovery stage, V-th 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.