Fabrication of microwave planar germanium transistors

Techniques have been developed for fabricating germanium planar transistors which are superior in performance to mesa types. This paper discusses the results of basic fabrication studies, summarizes the design of several different microwave planar germanium transistors and presents measurement results of encapsulated devices. With the planar process the junction area is limited by a mask. This is achieved by depositing SiO2on the surface of the germanium and etching a window in the oxide by photoengraving technique to define the base area. The remaining oxide acts as a mask against diffusion.