Swift, Thomas Hugh; (2025) Characterisation of superconductors and quantum dots in 22nm-node CMOS devices. Doctoral thesis (Ph.D), UCL (University College London).

Text PhD Thesis - Thomas Hugh Swift.pdf - Accepted Version Access restricted to UCL open access staff until 1 April 2026. Download (26MB)

Abstract

Silicon spin qubits are a promising platform for quantum computing, having already shown both long coherence times and high-fidelity operations. Importantly, they also offer a clear path to scalability given the similarity in structure between silicon quantum dots and transistors. To fully realise this scalability we must show that the results from academically fabricated devices can be translated into industrial-scale foundry processes. Here, I develop three fundamental building blocks of a future quantum processor using devices fabricated in GlobalFoundries’ 22 nm fully-depleted siliconon-insulator process. I demonstrate a double quantum dot in the low electron regime, high kinetic inductance thin films for compact readout and furthermore the ability to perform thermometry at milikelvin temperatures with microsecond resolution. To realise a double quantum dot in the low electron regime, I investigated a range of available device types including n/p-type channels and single vs multi-gate devices. For these I characterised the quantum dots using metrics including dot quality, 1st electron voltage and charge noise. In developing a compact readout approach, three different high kinetic inductance thin films were characterised using a large set of multiplexed devices. The superconducting characteristics of these films were then extracted, including critical current, critical field and critical temperature. Furthermore, extensive work on thermometry was performed using a wide range of techniques including gate-resistance, superconducting phase transition, dc diode and rf diode thermometry. This allowed me to better understand the dynamic behaviour of cross-chip temperatures at varying timescales down to the microsecond-level.

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