A QUANTUM GATE CURRENT MODEL

Gate current plays a critical role in the maximum gate voltage swing, the maximum transconductance, and as a direct consequence, the maximum noise margin of digital devices. A quantum gate current model based o n a charge-control analysis and the WKB approximation is presented for heterostructure field effect transistors (HFET's). Both the tunneling and thermionic emission gate currents are included and treated in a u nified way in this model. Along with the general model itself, a speci fic calculation on a semiconductor insulator semiconductor (SISFET) is presented. Our model shows that for advanced HFET's with thin hetero- barrier layers, the tunneling component dominates over the thermionic component and essentially constitutes the gate current.