STUDY OF GaAs/AlGaAs MODFET INVERTERS AND RING OSCILLATORS.

Even though MODFET's are being considered for high-speed digital applications in which devices operate under large voltage swings, fundamental understanding of the MODFET inverter chains is lacking and present designs are based on ground rules developed by trial and error. Aided by quantum-mechanical numerical simulations of the transfer characteristics and experimental results obtained in our laboratory, a simple and straightforward model for the transfer characteristics agrees very well with data developed. High-frequency gate capacitance voltage characteristics (theory has been development and is being included in the inverter chain/active load model) were used with a desktop computer to predict the propagation delay, power dissipation, and noise margin for a wide range of supply voltage and load current at 300 and 77 K. Since the model includes all material and device parameters it can be used to optimize the design from heterojunction growth through inverter design both at 300 and 77 K.