High frequency, high power static induction transistors in silicon carbide: Simulation and fabrication
Abstract
The static induction transistor (SIT) in silicon carbide can provide very high total power at microwave frequencies. This is due to the vertical structure of the SIT which consists of a vertical channel that is defined by a mesa with gate electrodes of the Schottky type to control the current between a top side source contact and a drain contact on the backside of the wafer. The favorable material parameters of silicon carbide make it an ideal choice for the SIT. This thesis demonstrates that through careful modeling by means of simulations and inclusion of all significant device physics, good agreement is reached between theoretical prediction and measured results on real devices. It is shown in particular that by careful choice of the device parameters, SITs should be able to obtain transit frequencies up to 20GHz. The main approach to obtain fast devices is an increase in doping and a corresponding reduction of the device geometry. Aggressively scaled devices that consist of mesas that are 0.3 micron wide have been fabricated and show a record transit frequency of 9.1GHz. The frequency response is limited by extrinsic device parasitics such as contact resistance and parasitic capacities. Additionally, an inverted SIT is introduced that interchanges the roles of source and drain and is predicted to double the bandwidth that is possible with broadband amplifiers that can be achieved with SITs. A prototype structure has been fabricated and shows static characteristics that compare favorably with the standard design and has reduced parasitic capacities as predicted by simulations. To facilitate circuit design, a large signal model has been developed that is based on measured device performance and will allow the development of amplifiers that employ SITs. Some preliminary design considerations are presented, together with suggestions to further reduce parasitics.
Degree
Ph.D.
Advisors
Cooper, Purdue University.
Subject Area
Electrical engineering
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