56% PAE mm-Wave SiGe BiCMOS Power Amplifier Employing Local Backside Etching

This letter presents a power amplifier (PA) with excellent power-added efficiency (PAE) for millimeter-wave (mm-wave) applications. The high efficiency is achieved by leveraging a local backside etching (LBE) process to enhance the quality factor (Q) of the output matching network. The PA was fabricated in a mature SiGe BiCMOS technology featuring heterojunction bipolar transistors (HBTs) having an $ {f}_{T} / {f}_{\max } $ of 250/340 GHz. While the measured peak PAE is 56% at 24 and 25 GHz, the PA provides 16 dB of peak gain and a 3-dB bandwidth of 19 GHz ranging from 13.5 to 32.5 GHz, which makes the circuit well suited for multiple purposes, such as sensors, radars, 5G, and satellite communications. The maximum PAE exceeds 40% from 22 to 28 GHz, with a peak saturated power ( $ {P}_{\text {sat}} $ ) of 16.5 dBm at 25 GHz. To the best of authors’ knowledge, this PA achieves the highest PAE reported to date for silicon-based mm-wave amplifiers.