InP/GaAsSb DHBTs: THz Analog Performance and Record 180-Gb/s 5.5Vppd-Swing PAM-4 DAC-Driver

“Type-II” InP/GaAsSb DHBTs are the first non-GaInAs -based transistors to show oscillation frequencies > 1 THz with the associated benefits of higher breakdown voltages, low power dissipation, and superior linearity characteristics. Whereas no large-signal characterization of THz transistors is found in the literature, THz InP/GaAsSb DHBTs display attractive 94 GHz load-pull characteristics, and less aggressively scaled devices achieve record saturated output power and output power density per unit emitter area. The physical advantages of Type-II InP/GaAsSb are reviewed here. Beyond impressive analog small/large-signal performance metrics, we report a record digital performance for a PAM-4 DAC-driver designed and fabricated at III-V Lab in a 0.7-um InP/GaAsSb DHBT technology, based on epitaxial layers grown at ETHZ. The DAC-driver offers an unprecedented 5.5-Vppd 90-GBd (180 Gb/s) differential output swing with high eye diagram quality and over 12-dB gain control capability at a 1.1-W power consumption, leading to a record 3.1-GBd E/O modulator driver figure-of-merit. A 110 GHz bandwidth linear driver with a 16.7 dB gain and 0.85 W consumption was also implemented in the same technology, enabling a 4.1-Vppd output swing at 100 Gb/s both in PAM-4 and NRZ signaling. The all-around outstanding performance of InP/GaAsSb DHBTs makes them attractive for a wide variety of analog and mixed-signal circuit blocks used in modern telecommunication applications.