PREPARATION AND RF PROPERTIES OF MIS MESA VARACTORS.

Compared with the usual structure of MIS varactors the upside-down mesa varactor has two advantages which are significant for microwave power circuits: the thermal resistance of the substrate is eliminated, and the substrate thickness can be reduced to the extent that its losses are negligible. The preparation process for an MIS upside-down mesa structure and methods for rf measurements are described. It is shown that the losses at 3 GHz consist mainly of the inevitable epilayer resistance and that the mesa etching process does not degrade varactor properties, such as surface state density and breakdown voltage. An improved structure suitable for passivation and further reduction of the thermal resistance is proposed.