An analytical threshold voltage and subthreshold current model for short-channel AlGaAs/GaAs MODFETs

Short-channel effects on the subthreshold behavior are modeled in self-aligned gate AlGaAs/GaAs MODFETs through an analytical solution of the two-dimensional Poisson equation in the subthreshold region. Based on the resultant potential solution, simple and accurate analytical expressions for short-channel threshold voltage, subthreshold swing, and subthreshold drain current are derived. These are then used to develop an expression for minimum acceptable channel length. A comparative study of short-channel effects in enhancement-mode MODFETs with and without i-AlGaAs spacer layers indicates that channel lengths will be limited to 0.18-0.25 μm by subthreshold conduction. Minimum gate lengths for MODFETs with a spacer layer are notably larger than those without a spacer layer. Besides offering insights into the physics of short-channel effects in MODFETs, the model provides a useful basis for efficient design, analysis, and simulation of small geometry AlGaAs/GaAs MODFET digital circuits