A bipolar junction transistor (BJT) requires the fabrication of a BJT
structure and of a support post which is adjacent to, but physically and
electrically isolated from, the BJT structure. The BJT structure includes
a semi-insulating substrate, a subcollector, a collector, a base, and an
emitter. Metal contacts are formed on the subcollector and emitter to
provide collector and emitter terminals. Contact to the structure's base
is accomplished with a metal contact which extends from the top of the
support post to the edge of the base nearest the support post. The contact
bridges the physical and electrical separation between the support post
and the base and provides a base terminal for the device. The base contact
need extend over the edge of the base by no more than the transfer length
associated with the fabrication process. This results in the smaller base
contact area over the collector than would otherwise be necessary, and a
consequent reduction in base-collector capacitance. The invention is
particularly useful when forming heterojunction bipolar transistors
(HBTs), built on a compound semiconductor substrate such as indium
phosphide (InP).
