Evan Golden

Fabrication of superconducting through-silicon vias

  1. Justin L. Mallek,
  2. Donna-Ruth W. Yost,
  3. Danna Rosenberg,
  4. Jonilyn L. Yoder,
  5. Gregory Calusine,
  6. Matt Cook,
  7. Rabindra Das,
  8. Alexandra Day,
  9. Evan Golden,
  10. David K. Kim,
  11. Jeffery Knecht,
  12. Bethany M. Niedzielski,
  13. Mollie Schwartz,
  14. Arjan Sevi,
  15. Corey Stull,
  16. Wayne Woods,
  17. Andrew J. Kerman,
  18. and William D. Oliver
Increasing circuit complexity within quantum systems based on superconducting qubits necessitates high connectivity while retaining qubit coherence. Classical micro-electronic systems
have addressed interconnect density challenges by using 3D integration with interposers containing through-silicon vias (TSVs), but extending these integration techniques to superconducting quantum systems is challenging. Here, we discuss our approach for realizing high-aspect-ratio superconducting TSVs\textemdash 10 μm wide by 20 μm long by 200 μm deep\textemdash with densities of 100 electrically isolated TSVs per square millimeter. We characterize the DC and microwave performance of superconducting TSVs at cryogenic temperatures and demonstrate superconducting critical currents greater than 20 mA. These high-aspect-ratio, high critical current superconducting TSVs will enable high-density vertical signal routing within superconducting quantum processors.
arxiv pdf

Comparison of Dielectric Loss in Titanium Nitride and Aluminum Superconducting Resonators

  1. Alexander Melville,
  2. Greg Calusine,
  3. Wayne Woods,
  4. Kyle Serniak,
  5. Evan Golden,
  6. Bethany M. Niedzielski,
  7. David K. Kim,
  8. Arjan Sevi,
  9. Jonilyn L. Yoder,
  10. Eric A. Dauler,
  11. and William D. Oliver
Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics
in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide (CPW) resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region’s contribution to resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal-air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric (HF) etch, and find that it reduced losses from the substrate-air interface, thereby improving the quality factor.
arxiv pdf

Determining interface dielectric losses in superconducting coplanar waveguide resonators

  1. Wayne Woods,
  2. Greg Calusine,
  3. Alexander Melville,
  4. Arjan Sevi,
  5. Evan Golden,
  6. David K. Kim,
  7. Danna Rosenberg,
  8. Jonilyn L. Yoder,
  9. and William D. Oliver
Superconducting quantum computing architectures comprise resonators and qubits that experience energy loss due to two-level systems (TLS) in bulk and interfacial dielectrics. Understanding
these losses is critical to improving performance in superconducting circuits. In this work, we present a method for quantifying the TLS losses of different bulk and interfacial dielectrics present in superconducting coplanar waveguide (CPW) resonators. By combining statistical characterization of sets of specifically designed CPW resonators on isotropically etched silicon substrates with detailed electromagnetic modeling, we determine the separate loss contributions from individual material interfaces and bulk dielectrics. This technique for analyzing interfacial TLS losses can be used to guide targeted improvements to qubits, resonators, and their superconducting fabrication processes.
arxiv pdf