Effects of hot carriers in offset gated polysilicon thin-film transistors

The effects of hot carriers on the characteristics of intrinsic offset gated n-channel polysilicon thin-film transistors (TFTs), with channel length L = 10 μm, have been studied in relation to the offset length ΔL. From the evolution of the transfer and output characteristics during stress, the degree of the device degradation is deduced. In devices with ΔL = 0.5 and 1 μm, the on-state current is substantially reduced, whereas the subthreshold region remains almost unaffected. In devices with ΔL = 2 μm, the transfer characteristics are shifted first positively after short stressing time and then negatively, the on-state current is still substantially reduced and well-defined kink is formed in the subthreshold region. The device degradation is found to become more pronounced as the gate offset length increases. A model explaining the post-stress performance of offset gated devices is presented.