Determination of excess current due to impact ionization in polycrystalline silicon thin-film transistors

Polysilicon thin-film transistors (TFTs) are of great interest for their circuit application in the large area microelectronics. A successful circuit design requires an accurate prediction of the circuit performances, which in turn needs a proper modeling of the electrical device characteristics. In this present work the specific aspects of the anomalous current increase in the output characteristics, often called the “kink” effect, are analysed. A new procedure to determine the excess current is presented and we analysed the excess current for different gate voltages, temperatures and device geometries. We show that, from the parameters that can be extracted by analysing a reduced set of experimental data, the excess current can be easily predicted for any bias and temperature condition and also for devices with different geometries. These results can be used to further up-grade the modeling of the electrical characteristics of polysilicon TFTs in circuit simulators.