An 85-watt dissipation silicon power transistor

Production prototype silicon transistors have been made using large area diffused base structures. Simultaneous diffusion of gallium and phosphorus is used to form the diffused base structures. The geometry and doping level of the structure can be controlled by varying the impurity source composition and temperature. The phosphorus surface concentration is a much less rapidly varying function of source temperature than is the gallium surface concentration, and is determined primarily by the source composition. Two line base contacts, one line emitter contact and a collector contact, are attached to the wafer by using appropriate alloys in conjunction with titanium or tungsten back-up plates. The structure then is encapsulated in a hermetically sealed package. The transistors are capable of dissipating 85 watts at a 25°C mounting base temperature and have been used in circuits, as is described, to deliver 25 watts Class A, 80 watts Class B in push-pull operation and peak currents of 10 amperes in pulsed operation.