This article presents a family of sub-1-V, fully-CMOS voltage references adopting MOS devices in weak inversion to achieve continuous operation from room temperature (RT) down to cryogenic temperatures. Their accuracy limitations due to curvature, body effect, and mismatch are investigated and experimentally validated. Implemented in 40-nm CMOS, the references show a line regulation better than 2.7%/V from a supply as low as 0.99 V. By applying dynamic element matching (DEM) techniques, a spread of 1.2% (3σ ) from 4.2 to 300 K can be achieved, resulting in a temperature coefficient (TC) of 111 ppm/K. As the first significant statistical characterization extending down to cryogenic temperatures, the results demonstrate the ability of the proposed architectures to work under cryogenic harsh environments, such as space- and quantum-computing applications.

LC VCOs with low phase noise (PN) and an octave frequency-tuning range (FTR) are required for multistandard communication devices, software-defined radios, and wireline data links. A viable popular approach is to exploit multicore mode-switching VCOs for two reasons: (1) their PN improves linearly by in-phase coupling of N identical VCOs; (2) the resonant-mode switching enhances the VCO FTR without degrading the tank quality factor (Q) as no RF current ideally flows through lossy mode-selection switches. However, it is still challenging for dual-mode VCOs to achieve a competitive FoM while covering an octave FTR at oscillation frequencies (F_OSC) above 6GHz [1]. To enhance the number of oscillation modes to 3, [2] added a center-loop inductor (L_C) to a transformer, as shown in Fig. 9.2.1. However, a large FTR gap is measured, since the transformer windings should be strongly coupled to accommodate L_C, The authors of [3] and [4] realized a triple- and quad-mode operation, respectively, by coupling two individual transformer-based resonators (see Fig. 9.2.1). Apart from the large area penalty, the former needs an extra third winding (L_T) in each transformer that degrades the tank Q, while the latter used large, fixed coupling capacitors (C_M) that load the tank in two of the resonant modes, thus limiting the VCO FTR.

We demonstrate a 36 × 36 gate electrode crossbar that supports 648 narrow-channel field effect transistors (FET) for gate-defined quantum dots, with a quadratic increase in quantum dot count upon a linear increase in control lines. The crossbar is fabricated on an industrial ²⁸Si-MOS stack and shows 100% FET yield at cryogenic temperature. We observe a decreasing threshold voltage for wider channel devices and obtain a normal distribution of pinch-off voltages for nominally identical tunnel barriers probed over 1296 gate crossings. Macroscopically across the crossbar, we measure an average pinch-off of 1.17 V with a standard deviation of 46.8 mV, while local differences within each unit cell indicate a standard deviation of 23.1 mV. These disorder potential landscape variations translate to 1.2 and 0.6 times the measured quantum dot charging energy, respectively. Such metrics provide means for material and device optimization and serve as guidelines in the design of large-scale architectures for fault-tolerant semiconductor-based quantum computing.

This paper presents a 15b cryo-CMOS DAC for multiplexed spin-qubit biasing implemented in a 22-nm FinFET process. The integrating-DAC architecture and the robust digitally-assisted high-voltage output stage enable a low power dissipation (157W) and small area (0.08mm2) independent of the number of biased qubits, and a 3V output range well beyond the nominal supply. This represents the first scalable solution for cryo-CMOS qubit biasing, which achieves a 1.8× better voltage resolution with a lower DNL over a 3× larger output range than the current state-of-the-art.

Quantum-based systems, such as quantum computers and quantum sensors, typically require a cryogenic electrical interface, which can be conveniently implemented using CMOS integrated circuits operating at cryogenic temperatures (cryo-CMOS). Reliable simulation models are required to design complex circuits, but CMOS transistor electrical characteristics at cryogenic temperatures substantially deviate from the behavior at room temperature, and no standard physics-based model exists for cryo-CMOS devices. To circumvent those limitations, this paper proposes the use of Artificial Neural Networks (ANN) and an associated training (extraction) procedure that automatically generates cryo-CMOS device models directly from experimental data. A device model for the DC characteristics of 40-nm CMOS transistors over a wide range of bias conditions, device geometries and temperatures from 4 K to 300 K has been generated and used to simulate voltage-reference circuits over a wide temperature range (4 K - 300 K). The potential application to dynamic/high-frequency circuits is demonstrated by enhancing the basic model with ANN-based nonlinear multi-terminal capacitive elements to simulate a ring oscillator. Preliminary results showing a good match between simulations and experiments demonstrate the feasibility and practicality of the proposed approach.

Cryogenic CMOS (cryo-CMOS) is a viable technology for the control interface of the large-scale quantum computers able to address non-trivial problems. In this paper, we demonstrate state-of-the-art cryo-CMOS circuits and systems for such application and we discuss the challenges still to be faced on the path towards practical quantum computers.

CMOS circuits operating at cryogenic temperature (cryo-CMOS) are required in several lowerature applications. A compelling example is the electronic interface for quantum processors, which must reside very close to the cryogenic quantum devices it serves, and hence operate at the same temperature, so as to enable practical large-scale quantum computers. Such cryo-CMOS circuits must achieve extremely high performance while dissipating minimum power to be compatible with existing cryogenic refrigerators. These requirements asks for cryo-CMOS electronics on par with or even exceeding their roomerature counterparts. This paper overviews the challenges and the opportunities in designing cryo-CMOS circuits, with a focus on analog and mixed-signal circuits, such as voltage references and data converters.

This paper presents a family of voltage references in standard 40-nm CMOS that exploits the temperature dependence of dynamic-threshold MOS,NMOS and PMOS transistors in weak inversion to enable operation over the ultra-wide temperature range from 4.2 K to 300 K. The proposed references achieve a temperature drift below 436 ppm/K over a statistically significant number of samples after a single-point trim and a supply regulation better than 1.7 %/V from a a supply as low as 0.99 V. These results demonstrate,for the first time,the generation of PVT-independent voltages over an ultra-wide temperature range using sub-1-V nanometer CMOS circuits,thus enabling the use of the proposed references in harsh environments,such as in space and quantum-computing applications.