Positive bias temperature instability evaluation in fully recessed gate GaN MIS-FETs

In this paper, positive bias temperature instability (PBTI) in fully recessed gate GaN MIS-FETs is studied by using an eMSM (extended Measure-Stress-Measure) technique, which consists of a set of stress/recovery tests. By using this technique, V_TH shift after a stress and the relaxation information can be collected in one experiment. First of all, a typical forward-reverse gate sweep and frequency-dependent conductance method are used to characterize V_TH shift and interface state density (D_it) in fully recessed gate MIS-FETs with two different gate dielectrics (PEALD SiN and ALD Al₂O₃), showing that ALD Al₂O₃ has a smaller V_TH shift compared with PEALD SiN although the latter has a smaller Dit. Then, an eMSM technique is used to understand the trapping/de-trapping phenomena under stress and relaxation period. The results show a power law dependency of V_TH shift with respect to the stress time. Furthermore, the voltage dependency of V_TH shift (7) can be extracted, showing that ALD Al₂O₃ has a higher 7 compared to PEALD SiN. The physical model is proposed to explain the mechanism for the different voltage dependency. On the other hand, the relaxation data is collected as well, indicating that Al₂O₃ has a faster relaxation even under a high voltage overdrive stress, which is consistent with physical model since accessibility of defects in Al₂O₃ are located at energies less favorable for channel carriers, compared to SiN.