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In this letter, we characterize the electrical properties of commercial bulk 40-nm MOSFETs at room and deep cryogenic temperatures, with a focus on quantum information processing (QIP) applications. At 50 mK, the devices operate as classical FETs or quantum dot devices when either a high or low drain bias is applied, respectively. The operation in classical regime shows improved transconductance and subthreshold slope with respect to 300 K. In the quantum regime, all measured devices show Coulomb blockade. This is explained by the formation of quantum dots in the channel, for which a model is proposed. The variability in parameters, important for quantum computing scaling, is also quantified. Our results show that bulk 40-nm node MOSFETs can be readily used for the co-integration of cryo-CMOS classical-quantum circuits at deep cryogenic temperatures and that the variability approaches the uniformity requirements to enable shared control.

We fabricated linear arrangements of multiple splitgate devices along an SOI mesa, thus forming a 2×N array of individually controllable Si quantum dots (QDs) with nearest neighbor coupling. We implemented two different gate reflectometry-based readout schemes to either probe spindependent charge movements by a coupled electrometer with single-shot precision, or directly sense a spin-dependent quantum capacitance. These results bear significance for fast, high-fidelity single-shot readout of large arrays of foundrycompatible Si MOS spin qubits.

In this article, a cryo-CMOS receiver integrated with a frequency synthesizer for scalable multiplexed readout of qubits is presented, focusing on radio frequency (RF) reflectometry readout of silicon-based semiconductor spin qubits/quantum dots. The proposed spin qubit readout chip consists of a wideband low noise amplifier (LNA), a quadrature mixer, a complex filter, a pair of in-phase/quadrature (I/Q) intermediate frequency (IF) amplifier chains, and a type-II charge-pump phase-locked loop (PLL) with a programmable frequency divider providing local oscillator (LO) signals. Noise optimizations are applied to the LNA design and the quadrature active mixer design to obtain the required performance. A mode-switching complementary voltage-controlled oscillator (VCO) is proposed to achieve low-power and low-phase noise in a wide-frequency tuning range (46.5%). Circuit modifications and design considerations for robust cryogenic temperature operation are presented and discussed. Measurements show that the receiver provides an average gain of 65 dB, a minimum noise figure of 0.5 dB, an IF bandwidth of 0.1-1.5 GHz, and an image rejection ratio of 23 dB at 3.5 K with a power consumption of 108 mW. This cryo-CMOS receiver with frequency synthesizer for spin qubit readout is a first step toward fully-integrated qubit readout and control.