A Physically Based Compact Model of Partially Depleted MOSFETs for Analog Circuit Stimulation

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Description/Abstract

In this paper, the Southampton Thermal Analogue (STAG) compact model for partially depleted (PD) silicon-on-insulator (SOI) MOSFETs is presented. The model uses a single expression to model the channel current, thereby ensuring continuous transition between all operating regions. Furthermore, care has been taken to ensure that this expression is also infinitely differentiable, resulting in smooth and continuous conductances and capacitances as well as higher order derivatives. Floating-body effects, which are particular to PD SOI and which are of concern to analog circuit designers in this technology, are well modeled. Small geometry effects such as channel length modulation (CLM), drain-induced barrier lowering (DIBL), charge sharing, and high field mobility effects have also been included. Self-heating (SH) effects are much more apparent in SOI devices than in equivalent bulk devices. These have been modeled in a consistent manner, and the implementation in SPICE3f5 gives the user an additional thermal node which allows internal device temperature rises to be monitored and also accommodates the modeling of coupled heating between separate devices. The model has been successfully used to simulate a variety of circuits which commonly cause problems with convergence. Due to its inherent robustness, the model can normally achieve convergence without recourse to the setting of initial nodal voltage estimates.