High-speed AlGaAs/GaAs HBTs and their applications to 40-Gbit/s-class ICs

We developed IC-oriented high-performance AlGaAs/GaAs heterostructure bipolar transistors (HBTs). The parasitic effects of the HBTs are reduced by a self-aligned process technology characterized by a technique for making a base-metal-overlaid (BMO) structure, and the electron transit time in the HBTs is decreased by the novel collector structure of a "ballistic collection transistors with a launcher (LBCT)". The BMO-LBCT with a relatively thin collector had a cutoff frequency f/sub T/ of 171 GHz. By modifying collector thickness and using Pt-Ti-Pt-Au as the base ohmic metal, the maximum oscillation frequency f/sub max/ reached 148 GHz with a 114 GHz f/sub T/. Moreover, an MOCVD-grown highly-carbon-doped structure had an f/sub max/ of 192 GHz while still having an f/sub T/ more than 100 GHz. Using BMO-LBCTs, we successfully fabricated high-speed ICs: a 2:1 multiplexer with retiming D-type flip-flops that operates error-free at 19 Gbit/s, selector IC that operates at 40 Gbit/s, a divided-by-four dynamic frequency divider that functions up to 50 GHz, and a broadband preamplifier with a high gain of 16.8 dB and 3-dB-down bandwidth of 40 GHz.