New observations on the damage relaxation mechanisms in p-MOSFETs under dynamic NBTI stressing

Owing to its impact on circuit operation, the degradation of pMOSFETs under dynamic NBTI stressing has been intensively studied. Of specific interest is the damage recovery phenomenon, which eases the constraints imposed by static stress. This paper presents new observations on the relationship between threshold voltage shift (|/spl Delta/V/sub t/|) and interface states (/spl Delta/N/sub it/), for different dynamic NBTI stress modes. Results from unipolar stressing reveal a unique two-stage relaxation behavior. In the first stage, reduction in damage involves nearly equal relaxation of /spl Delta/N/sub it/ and the associated NBTI induced positive charge trapping (/spl Delta/N/sub ot/). A subsequent transition to a second stage, involving a more rapid relaxation of /spl Delta/N/sub ot/, is observed beyond a certain damage level. This finding implies that /spl Delta/N/sub ot/, relaxation has an equally important, if not, a more dominant impact, compared to /spl Delta/N/sub it/, relaxation, on the dynamic NBTI reliability of the p-MOSFET.