26-GHz etched-groove silicon permeable base transistor

A report is presented on the fabrication of etched-groove silicon permeable base transistors (PBTs) that reveal a maximum frequency of oscillation and a unity-current-gain cutoff frequency of 26 GHz, the latter being the highest value yet reported for Si PBTs. This performance was achieved with mushroom-shaped source fingers, a structure that permits both the passivation of the Si finger sidewalls and the reinforcement of the platinum gate with a gold overlayer. The doping distribution was optimized with two-dimensional numerical simulations, parasitic capacitances were reduced using a multilayer polyimide structure, and deep-UV optical lithography was used to fabricate PBTs with 0.2- to 0.4- mu m finger widths.<>