A 1 mW Cryogenic LNA Exploiting Optimized SiGe HBTs to Achieve an Average Noise Temperature of 3.2 K from 4–8 GHz

Low-power cryogenic LNAs are required for readout of fault-tolerant quantum processors, which may have a million or more qubits. While today, InP HEMT LNAs are used for qubit readout, SiGe HBTs are attractive for future systems due to their excellent noise and potential for low power operation. Here, we optimize a high performance SiGe technology to further improve its cryogenic noise properties. After extracting simulation models from standard and optimized HBT test structures, we employ these transistors in cryogenic LNAs and show that the cryogenic noise achieved with the optimized transistor is significantly better than that achieved using the standard device. Moreover, while dissipating just 1 mW, the amplifier using the optimized HBT had an average measured Te of 3.2K from 4–8 GHz, which is more than 2× better than the previous state-of-the-art SiGe LNA operating in this band.