Adaptation and comparative analysis of HSPICE level-61 and level-62 model for a-IGZO thin film transistors

This paper presents a Computer-aided design (CAD) model for a-IGZO thin film transistors (TFTs) by adapting SPICE level-61 RPI a-Si: H (Hydrogenated Amorphous Silicon) TFT model and level-62 RPI Poly-Si (Poly Silicon) TFT model. This work provides a complete understanding of SPICE level-61 and 62 model parameters, which must be tuned for a-IGZO TFT simulation. The adapted SPICE models of level-61 and level-62 could model all regions of operation of the TFT, that is, above-threshold and below-threshold regions. Adapted RPI poly-Si model also shows the kink effect in ZnO thin film transistors (TFTs) due to the recombination of electron-hole pairs in the channel via boundary trap states present in the poly-Si TFTs thereby increasing the drain current in the transistors above pinch-off region. The extracted performance parameters of the adapted models were found to be contiguous with experimental results. The maximum deviation in the subthreshold slope is approximately 5 mV/decade for level-61 a-Si TFT, and for level-62 poly-Si TFT, deviation in the subthreshold slope is even less, that is, 0.2 mV/decade. The experimental and simulated characteristics, extracted on-to-off ratio, negative bias reverse saturation current, and threshold voltage were almost similar. However, an average deviation of 2.4% and 2.27% was observed in the output characteristics of the adapted level-61 and level-62 models, respectively.