Bogdan Govoreanu

Silicon spin qubits based on metal–oxide–semiconductor (MOS) technology are compatible with semiconductor manufacturing and offer a route to scalable quantum processing. However, spin readout typically relies on proximal charge sensors, which add architectural complexity and limit qubit connectivity. In situ dispersive readout techniques are more compact, which can alleviate these constrains, but exhibit limited sensitivity. Here we report a radiofrequency electron-cascade readout method that enhances the dispersive signal through alternating-current electron co-tunnelling. With this approach, we achieve an enhancement in signal-to-noise ratio of more than 35 dB, leading to a minimum integration time of 7.6 ± 0.2 µs. We demonstrate singlet-triplet readout of two-electron spins in a natural silicon planar MOS quantum dot array, and coherent spin control using the exchange interaction, which forms the basis for entangling gates. We find dephasing times of up to 500 ns and a gate quality factor that exceeds 10.

Surface charge transfer doping (SCTD) has emerged as a promising technique for doping 2D semiconductors, although it faces challenges in doping controllability, which impacts device performance. In this study, we introduce a novel approach to precisely control the p-type doping strength in solid-state SCTD for 2D WSe₂ field-effect transistors (FET) through metal co-seeding. By sequentially depositing molybdenum (Mo) and hafnium (Hf) metal seeds followed by O₂ annealing, we achieve improved doping control, while maintaining a high on/off current ratio. High-resolution transmission electron microscopy (HRTEM) images confirm the proposed co-seeding concept. This technique addresses doping controllability limitations in SCTD, enhances gate tunability, and it is viable for very-large-scale integration (VLSI) applications.

Cryogenic semiconductor device models are essential in designing control systems for quantum devices and in benchmarking the benefits of cryogenic cooling for high-performance computing. In particular, the saturation of subthreshold swing due to band tails is an important phenomenon to include in low-temperature analytical MOSFET models as it predicts theoretical lower bounds on the leakage power and supply voltage in tailored cryogenic CMOS technologies with tuned threshold voltages. Previous physics-based modeling required to evaluate functions with no closed-form solutions, defeating the purpose of fast and efficient model evaluation. Thus far, only the empirically proposed expressions are in closed form. This article bridges this gap by deriving a physics-based and closed-form model for the full saturating trend of the subthreshold swing from room down to low temperature. The proposed model is compared against experimental data taken on some long and short devices from a commercial 28-nm bulk CMOS technology down to 4.2 K.

Cryogenic semiconductor device models are essential in designing control systems for quantum devices and in bench-marking the benefits of cryogenic cooling for high-performance computing. In particular, the saturation of subthreshold swing due to band tails is an important phenomenon to include in low temperature analytical MOSFET models as it predicts theoretical lower bounds on the leakage power and supply voltage in tailored cryogenic CMOS technologies with tuned threshold voltages. Previous physics-based modeling required to evaluate functions with no closed-form solutions, defeating the purpose of fast and efficient model evaluation. Thus far, only the empirically proposed expressions are in closed form. This article bridges this gap by deriving a physics-based and closed-form model for the full saturating trend of the subthreshold swing from room down to low temperature. The proposed model is compared against experimental data taken on some long and short devices from a commercial 28-nm bulk CMOS technology down to 4.2K

In this work, we report on the electrical performance of an ultra-low-power cryo-CMOS single-pole-4-throw (SP4T) RF multiplexer working at 10 mK base temperature stage of a dilution refrigerator. We use the multiplexer to benchmark a superconducting qubit for the very first time and obtain qubit coherence times of over 35 μs along with an average single-qubit gate fidelity of 99.93%, which exceeds the threshold required for quantum error-correction based on surface-code. This work demonstrates the operability of superconducting qubits with ultra-low-power cryo-CMOS devices at the base temperature, paving the way for advanced co-integration schemes.