Cryogenic & Precision Electronics

Contact: Fabio Sebastiano

My research goal is to interface integrated circuits with the world outside the silicon chip, both by building better sensor read-outs and by interacting with new computing devices. My research field is the design of analog and mixed-signal circuits. In the past, I have been working on sensor read-outs and integrated references, both in industry and academia. Currently, I am pushing the state-of-the-art of electronic interfaces for sensors and quantum devices. I will continue my quest in the future, by developing analog/mixed-signal electronics that will enable revolutionary applications, such as quantum computing.

Cryogenic interfaces

Quantum computers hold the promise to ignite the next technological revolution as the classical computer did for last century’s digital revolution, by efficiently solving problems that are intractable by today’s computers, such as large number factorization and simulation of quantum systems. Solid-state quantum processors must be typically cooled at cryogenic temperatures (<<1 K). In addition, a classical electronic controller is required to initialize, control and read out the quantum bits (qubits) at the core of the quantum processor. Currently, the most advanced quantum processors are equipped with less than 30 qubits, thus making it possible to connect a limited number of cables from the cryogenic refrigerator to a room-temperature electronic controller. However, quantum algorithms for practical applications require up to thousands or millions of qubits and of related connections, thus making the wiring to a room-temperature controller unpractical.

As an alternative, I propose a scalable CMOS electronic controller operating at cryogenic temperatures as close as possible to the quantum processor, in order to simplify the interconnect and to provide a solution scalable up to thousands of qubits. Although building a cryogenic CMOS controller is feasible, there are several challenges to be addressed. First, there is not yet a standard cryogenic model that can be embedded in commercial design tools and valid in the GHz-frequency range and/or for nanometer CMOS technologies. Missing reliable models strongly restrain the use of advanced techniques and the complexity of any circuit design. Second, specific cryogenic design techniques must be developed to deal with non-idealities of CMOS devices at cryogenic temperatures. Third, the cooling power of state-of-the-art refrigerators is limited to a few Watts at 4 K and well below 1 W at sub-K temperatures. This poses a strict specification on the power consumption of the electronics, thus forcing the average power consumption of the cryogenic controller below a few milliwatt per qubit.

More information on my research on cryogenic interfaces for quantum computers.

In addition to quantum computing, advances in cryogenic electronics will also be employed in many other low temperature applications. Examples include cryogenic sensors and/or electronic read-outs for high-energy physics experiments, detectors for radio-astronomy, cryogenic probes for nuclear magnetic resonance (NMR) used in chemical and medical spectroscopy ,and instrumentation for spacecraft and orbiting observatories.

Precision interfaces

This part of my research focus on the design of analog and mixed/signal electronics not necessarily at cryogenic temperature. It is mostly related to the electornic interfaces required to bring the information from a sensor into an integrated circuit.

Frequency references

Some applications ask for replacing the standard crystal oscillator with a fully integrated alternative. There may be several reasons, such as costs, size of the whole system and robustness to mechanical shocks. In particular, nodes for the Internet-of-Things (IoT) must often be extremely small and very cheap, so that they can be deployed in large number without affecting the surrounding environment. For such an application, avoiding the bulky quartz crystal by using an integrated alternative with the same accuracy is the holy grail. I gave a detailed overview of this topic in my ISSCC short course in 2016.

In the past, I developed a frequency reference based on the mobility of a MOS transistor, and I studied how to optimize the communication and architecture of an IoT node to use such a reference [1, 2, 3, 4].

Currently, I am working both on RC-based frequency references and on thermal-diffusivity-based frequency references [5].

Temperature sensors

Integrated temperature sensors are required in several applications, from the measurement of environmental temperature to the compensation of other sensors’ cross-sensitivities.

In the past, I optimized temperature sensor for nanometer CMOS technologies, achieving a 10x improvement
in accuracy over the state-of-the-art and building a temperature sensors that isstill today the most accurate temperature sensor in a CMOS technology with feature size below 100 nm [6].

Currently, I am working on minimizing the area of temperature sensor for thermal-monitoring applications in SoC’s and microprocessors by using sensors based
on silicon thermal diffusivity [7]. Next to that, I am exploring new methods for tmeperature sensing based on measuring thermal noise.

Analog-to-Digital Converters

I am also working on analog-to-digital converters that combines an energy-efficient SAR converter and an high-accuracy ΣΔ converter to achieve state-of-the-art performance [8].

References

[1] F. Sebastiano, L. J. Breems, K. A. A. Makinwa, S. Drago, D. M. W. Leenaerts, and B. Nauta, “A Low-Voltage Mobility-Based Frequency Reference for Crystal-Less ULP Radios,” IEEE J. Solid-State Circuits, vol. 44, iss. 7, pp. 2002-2009, 2009.
[2] F. Sebastiano, L. J. Breems, K. Makinwa, S. Drago, D. M. W. Leenaerts, and B. Nauta, “A 65-nm CMOS temperature-compensated mobility-based frequency reference for Wireless Sensor Networks,” IEEE J. Solid-State Circuits, vol. 46, iss. 7, pp. 1544-1552, 2011.
[3] S. Drago, F. Sebastiano, L. J. Breems, D. M. W. Leenaerts, K. A. A. Makinwa, and B. Nauta, “Impulse-Based Scheme for Crystal-Less ULP Radios,” IEEE Trans. Circuits Syst. I, vol. 56, iss. 5, pp. 1041-1052, 2009.
[4] F. Sebastiano, L. J. Breems, and K. A. A. Makinwa, Mobility-based Time References for Wireless Sensor Networks, Springer, 2013.
[5] L. Pedalà, &. Gürleyük, S. Pan, F. Sebastiano, and K. A. A. Makinwa, “A Frequency-Locked Loop Based on an Oxide Electrothermal Filter in Standard CMOS,” in Proc. European Solid-State Circuits Conference, Leuven, Belgium, 2017.
[6] F. Sebastiano, L. J. Breems, K. Makinwa, S. Drago, D. M. W. Leenaerts, and B. Nauta, “A 1.2-V 10-µW NPN-Based Temperature Sensor in 65-nm CMOS With an Inaccuracy of 0.2 °C (3σ) From -70 °C to 125 °C,” IEEE J. Solid-State Circuits, vol. 45, iss. 12, pp. 2591-2601, 2010.
[7] U. Sönmez, F. Sebastiano, and K. A. A. Makinwa, “Compact Thermal-Diffusivity-Based Temperature Sensors in 40-nm CMOS for SoC Thermal Monitoring,” IEEE Journal of Solid-State Circuits, vol. 52, iss. 3, pp. 834-843, 2017.
[8] B. Gönen, F. Sebastiano, R. Quan, R. van Veldhoven, and K. A. A. Makinwa, “A Dynamic Zoom ADC With 109-dB DR for Audio Applications,” IEEE Journal of Solid-State Circuits, vol. 52, iss. 6, pp. 1542-1550, 2017.

Projects under this theme

MSc students