Hot carrier effects in self-aligned and offset-gated polysilicon thin-film transistors

The effects of hot carriers on the transfer characteristics of self-aligned and offset-gated polysilicon thin-film transistors (TFTs), with channel length L = 10 mu m and offset length Delta L = 2 mu m, are investigated. In the self-aligned device, the on-state current is substantially reduced, whereas the subthreshold slope remains almost unaffected. In the offset gated device, the transfer characteristic is shifted first positively and then negatively, the on-state current is still substantially reduced and well-defined kinks are formed in the subthreshold region. The device degradation is found to become more pronounced in the offset gated device. A model explaining the post-stress performance of the offset-gated device is presented.