Emitter—Base—Collector self-aligned heterojunction bipolar transistors using wet etching process

The first emitter-base-collector (EBC) self-aligned (SA) heterojunction bipolar transistors (HBT's) using wet etching process are described. This self-alignment fabrication technique is extremely simple but can get excellent high-frequency performance. An HBT with a 4-µm-wide emitter mesa showed 18 GHz of F
t
and 13 GHz of
F_{\max}
. By optimizing this process, high-frequency operation above 40 GHz can be expected.