Cryogenic Characterization of a 5–6 GHz LC VCO for CMOS-Quantum Co-Integration

The amount of interconnections between the milli-Kelvin stage of a quantum computer to the ambient environment where the control electronics may reside is a limiting constraint in realizing scalable, many-qubit quantum computers. This limitation can be overcome by integrating the control electronics onto CMOS ASICs that operate at 4 K in physical proximity to the qubits. Such instrumentation relies, in part, on CMOS system building blocks such as voltage-controlled oscillators (VCO) in order to control and readout qubits, drive internal circuitry such as memories and state machines, and to communicate with the user. However, CMOS design and performance of VCOs at cryogenic conditions is not well characterized and accurate cryogenic design models do not exist. We design a VCO capable of operation at 300 K and characterize it down to 8 K, and we extract critical circuit parameters across temperature that will aid future cryogenic-CMOS designs.