Bipolar transistor characterization apparatus and method employing air bridge connectors to test probe pads

A test heterojunction bipolar transistor (HBT) structure, comprising:

• a substrate having an edge,
• a subcollector layer over said substrate having an edge stepped back from the substrate edge,
• a collector layer over said subcollector layer and a base layer over said collector layer, said collector and base layers having respective edges stepped back from said subcollector layer edge,
• an emitter layer over said base layer having an edge stepped back from said base layer edge,
• emitter and base pedestals on said substrate laterally spaced from said emitter and base layers, respectively,
• emitter and base test probe pads on said emitter and base pedestals, respectively, connected by respective emitter and base air bridges to respective emitter and base contacts on said emitter and base layers, respectively, and
• a collector test probe pad located lateral to said subcollector layer and connected by a collector lead to a subcollector contact on said subcollector.

A method of fabricating a test heterojunction bipolar transistor (HBT), comprising:

• forming subcollector, collector, base and emitter layers in a stack on a substrate,
• forming emitter, base and collector contact pads on said emitter, base and subcollector layers, respectively,
• forming emitter, base and collector test probe pads lateral to said emitter, base and subcollector layers, respectively, and
• forming electrically conductive test connections between said emitter, base and collector contact pads and said emitter, base and collector test probe pads, respectively,
• wherein at least one of said contact pads is formed simultaneously with its respective test probe pad and test connection.