Through silicon vias for the 3D integration of superconducting quantum circuits

Nugent, Nicholas P.H. (2025) Through silicon vias for the 3D integration of superconducting quantum circuits. PhD thesis, University of Glasgow.

Abstract

The development of superconducting quantum computing has seen a rapid acceleration in recent years. The number of controllable qubits fabricated on-chip has steadily increased in the pursuit of more computational power. 3D integration has become a key enabling technology for the scalability of these larger systems due to the architectural flexibility it offers, mirroring its impact on conventional electronics. As part of this development, superconducting throughsilicon vias (TSVs) have recently emerged as a method of breaking the wiring plane and routing signals through the substrate as well as for other, more novel, applications such as acting as the capacitive component of a new type of superconducting qubit.

This thesis will discuss the simulation, fabrication and measurement of superconducting TSVs. Using ANSYS HFSS electromagnetic simulation software, the geometric parameters of TSV-integrated co-planar waveguides were optimised for the transmission of microwave signals. In addition, a TSV-integrated tunable qubit coupler was simulated and the effect of the device’s geometry on the various capacitances within the device, and in turn on the device’s parameters, such as the charging and Josephson energies, was investigated. As a leading cause of signal degradation in electronic devices, crosstalk should be removed from devices as far as possible. Varying the number and arrangement of grounding TSVs was explored as a strategy for the mitigation of crosstalk between adjacent TSVs and it was found that using 4 ground TSVs to shield the signal TSV resulted in a dramatic reduction in crosstalk, with values of S41 <−140dB
at 4GHz.

For the fabricated samples, a comparison was made of different Bosch etches used to define the TSVs and it was determined that the ICP power and total etch time were highly influential in the degree of sidewall roughness. Methods of sidewall smoothing were also investigated, with KOH wet etching found to offer near atomic-level smoothness. Finally, the fabricated samples were characterised using, among other methods, cryogenic spectroscopy. A novel application of the method of calibrated cryogenic S-parameter measurement to superconducting TSVs is also presented, with the TSV-integrated co-planar waveguide structure under test exhibiting a peak transmission of -1.44dB.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Supervisor's Name: Weides, Professor Martin and Lindstrom, Dr. Tobias
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85355
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 17 Jul 2025 07:41
• Last Modified: 17 Jul 2025 07:48
• URI: https://theses.gla.ac.uk/id/eprint/85355