Growth of titanium-nitride thin films for low-loss superconducting quantum circuits

Olson, Gustaf Anders

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https://hdl.handle.net/2142/87951 Copy

Description

Title

Growth of titanium-nitride thin films for low-loss superconducting quantum circuits

Author(s)

Olson, Gustaf Anders

Issue Date

2015-05-29

Director of Research (if dissertation) or Advisor (if thesis)

Eckstein, James N.

Doctoral Committee Chair(s)

Bezryadin, Alexey

Committee Member(s)

• Clark, Bryan K
• Vieira, Joaquin

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Titanium-Nitride (TiN)
• Superconductivity
• Qubit
• Resonator
• Materials

Abstract

This is a study of the growth of titanium-nitride (TiN) by plasma assisted molecular beam epitaxy (MBE) for applications in low loss quantum circuits. Titanium nitride is a material known to have low loss at microwave frequencies which sees practical use in many emerging quantum device architectures. The goal of this research is to investigate improvements in TiN thin films utilizing MBE to produce highly pure, highly crystalline films. A review of the theory of superconducting qubits is given and recent developments in superconducting qubit research are summarized to elucidate how loss has been reduced historically and the importance of materials improvements to the future of scalable quantum computation. The dynamics of epitaxial film growth are discussed, focusing on the formation of a minimum energy surface, the thermally driven kinetics of atoms deposited on the surface, and how these lead to the formation of large scale crystalline domains in the film. An overview of the MBE growth chamber is given and the growth procedure for TiN is discussed. Transport and morphology measurement results are discussed for MBE TiN where, for optimized growth conditions, films are highly crystalline with superconducting transition temperatures(Tc) as high as Tc = 6.1K, matching the value for bulk crystals and exceeding all reported thin film values. Microwave loss measurements of transmission line resonators fabricated from these films are shown to have low-power quality factors(Q) as high as 200,000 and an increase to Q = 400,000 at high power, consistent with the saturation of two-level-systems (TLS) at high power. These results confirm a connection between the high quality crystalline materials produced in this work and low loss in quantum circuits.

Graduation Semester

2015-8

Type of Resource

text

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http://hdl.handle.net/2142/87951

Copyright and License Information

Copyright 2015 Gustaf Olson

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