MECHANISM OF DEVICE DEGRADATION IN N-CHANNEL AND P-CHANNEL POLYSILICON TFTS BY ELECTRICAL STRESSING

The effects of electrical stress on hydrogenat ed n- and p-channel polysilicon thin-film transistors (poly-TFT's) were investigated. The on-state caused the most significant degradation, while off-state and accumulation conditions resulted in negligible degradation. The on-state stress degraded the threshold voltage, trap-state density, and subthreshold sharpness of both n- and p-channel devices toward prehydrogenated values, and the rates of degradation increased with stressing biases. The field-effect mobility and leakage current, however, were not degraded by stressing. The mechanism of device degradation may be attributed to the metastable creation of gap states within the polysilicon channel as opposed to gate dielectric charge trapping or interface state generation. © 1990 IEEE