On-chip adiabatic demagnetisation refrigeration

Bettsworth, Francis (2025) On-chip adiabatic demagnetisation refrigeration. PhD thesis, Lancaster University.

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Abstract

This thesis describes the thermal modelling and simulation of on-chip adiabatic demagnetisation refrigeration. On-chip cooling is a novel refrigeration technique which has been developed to solve the apparent poor thermalisation of electrons in microkelvin nanoelectronics. Micrometre- and nanometre-scale electronics are fundamental to the development of quantum technologies and hot electrons often degrade the performance of these devices. Microkelvin electron temperatures, will allow for the investigation of new physical phenomena and exotic electronic states of matter. Prior to this work, microkelvin electron temperatures have been produced by a combination of on-chip and off-chip refrigeration. The combination of cooling elements obfuscates the importance and necessity of off-chip cooling components. Without a complete description of on-chip cooling thermal dynamics, this combination of techniques also complicated the optimisation of on-chip refrigeration. This thesis presents a first-principles thermal model and simulation of on-chip demagnetisation refrigeration. This work finds that the thermal dynamics of a coulomb blockade thermometer with on-chip cooling are well-captured by this model. Using the simulation, this work explores the limits, constraints and optimisation of on-chip cooling. The results of this exploration outline a path towards microkelvin electrons in a 10 mK refrigerator with on-chip demagnetisation cooling.