Dynamic bias temperature instability of p-channel polycrystalline silicon thin-film transistors

The impact ionization that occurred near channel-S/D junctions is responsible for the dynamic bias temperature instability (BTI) of p-channel poly-Si thin-film transistors (TFTs). Impact ionization is induced by lateral electric field when gate voltage switches from inversion or full-depletion to accumulation bias. Drain current increases initially due to shortened effective channel length. As the stress time increases, the grain barrier height increases to reduce the drain current, especially at high temperature. In addition to the transient switches, the plateau portions of the gate pulse have significant impact on the device degradation for large stress amplitudes.