Energy Efficient Sensing using Steep Slope Devices

Today, we are witnessing the Internet of Things (IoT) revolution, which facilitates and improves ourlives in many aspects, but comes with several challenges related to the technology deployment atlarge scales. Handling ever growing amounts of information that needs to be sensed, stored,transmitted and processed requires severe improvements in energy efficiency and smart distributionof computational power spanning from Cloud systems (handling Big Data in a massively parallelfashion) all the way to Edge devices (interfaces to the real world), where co-integration of sensingand computation plays a big role. Innovations in this field require the development of new deviceprinciples in existing technology platforms and/or new abundant and non-toxic materials that canenable electronic functions beyond the classical semiconductors, such as the field of oxideelectronics that holds promise for both classical electronics functions and for future neuromorphicimplementations. In this thesis, we explore both these aspects, having as a common denominatorsteep slope devices, which have the merit of offering a path for improved energy efficiency viavoltage scaling. We particularly focus our work on their ability to serve energy efficient sensingfunctions that can be integrated with the computational platforms.The first part of the thesis focuses on Tunnel Field Effect Transistors (TFETs) and how they can beused to perform similar tasks to Single Electron Transistors for qubit readout and also for serving asinterfacing electronics. Such applications rely on cryogenic operation where conventional CMOStechnology shows performance degradation due to low temperature effects such as dopantdeactivation and carrier freeze-out. Our study shows that state-of-the-art heterostructure nanowireTFET arrays maintain excellent figures of merit over wide temperature ranges, down to the Kelvinregime, while simultaneously showing reduced temperature dependence once Trap AssistedTunnelling mechanisms are removed below 150K. Leveraging such properties, we suggest thatTFETs are promising candidates as charge sensing devices for qubit readout architectures with highsensitivity to single or few elementary charges.In the second part of the thesis we focus towards sensing architectures more suitable forEdge-of-Cloud (EoC) applications, by exploring phase-transition materials such as VanadiumDioxide (VO2). In this context, we explore the optimization of a Pulsed Laser Deposition (PLD)process in order to achieve high quality VO2thin films grown on CMOS compatible substrates,followed by electrical characterization of fabricated VO2two-terminal devices, which providesvaluable data that aid us in developing compact SPICE-compatible device models. Built on top ofthe VO2 resistor elements, we propose a novel Spiking Voltage-Controlled Oscillator (VCO)architecture that exhibits low device count (1 Transistor 1 Resistor - 1T1R) while at the same timeproviding frequency tuning capabilities in excess of 400% in the 10s of kHz range. Weexperimentally validate that the VCO cell can be used as a power-to-frequency transducer in a widespectrum, ranging from near-UV, throughout the entirety of the visible domain, and as far as theMid-Infrared and mmWave ranges, suggesting a new class of sensors capable of responding to abroad range of stimuli.