480-GHz $f_{\max}$ in InP/GaAsSb/InP DHBT With New Base Isolation $\mu$-Airbridge Design

Self-aligned
$\hbox{0.55}\times \hbox{3.5}\ \mu \hbox{m}^{2}$
emitter InP/GaAsSb/InP double heterojunction bipolar transistors demonstrating an
$f_{t}$
of 310 GHz and an
$f_{ \max}$
of 480 GHz are reported. Common–emitter current gain of 24, together with a breakdown voltage of 4.6 V, is measured. The devices were fabricated with a triple-mesa process and easily fabricated with a new base isolation
$\mu$
-airbridge design which, moreover, significantly reduced the base–collector capacitance
$C_{\rm BC}$
.