Large-signal Time-domain Simulation Of Millimelter-wave Transistors

INTRODUCTION It is well established that conduction elecmns in submicron devices can experience significant velocity overshoot, and can travel hna-device distances with picosecond transit times. A variety of novel transistor concepts, some involving heterojunctions or superlamces, have been proposed to take advantage of this. Such devices are often referred to generically as ’ballistic’ transistors. Simple analyses invariably predict excellent millimeter-wave and submillimeter-wave performance for ballistic transiston. These performance projections have generated widespread excitement and publicity. Articles about ballistic transistors have appeared in publications as diverse as IEEE Spectrum and the Wall Street Journal. Predictions that ballistic trans~~tors will soon operate at 500 GHz are common (e.g. [I]). and fresuency projections as high as 10 THz have appeared [2]. This paper articulates a different view of the performance potential of ‘ballistic’ transistors: that the excitement and optimism is clearly excessive. The paper has two parts. The fint part outlines why the ambitious published performance projections are much too optimistic. The second part presents an overview of the issues, techniques and problem involved in using large-signal time-domain simulation to obtain more realistic performance projections.