Janine Lorenz

Contactless terahertz mapping of wafer-scale superconducting NbTiN thin films

  1. Yayi Lin,
  2. Marc Neis,
  3. Marcello Pio Guardascione,
  4. Janine Lorenz,
  5. Thomas J. Smart,
  6. F. Stefan Tautz,
  7. Felix Lüpke,
  8. Frederik Bolle,
  9. Martin Dressel,
  10. Rami Barends,
  11. Pavel A. Bushev,
  12. and Marc Scheffler
For large-scale superconducting quantum technology, e.g. quantum computing, the homogeneity of wafer-scale superconducting thin films is vital for consistent performance of the fabricated
devices. Terahertz (THz) spectroscopy as a contactless and non-destructive measurement technique is a powerful tool to characterize the superconducting films. In this work, a set of niobium titanium nitride (NbTiN) thin films on 4-inch and 6-inch silicon wafers, grown via plasma-enhanced magnetron sputtering, are investigated via THz spectroscopy: full wafers are mapped at room temperatures and exemplary segments are characterized at cryogenic temperatures. The deviations in observed sheet resistance depend on the used deposition device and the film thickness. While the deviations in superconducting sheet kinetic inductance match those of the normal-state sheet resistance, the critical temperature and energy gap exhibit little variation. This THz mapping technique demonstrates the feasibility of evaluating wafer-scale superconducting thin films before lithography, facilitating preparation of the thin films for reproducible device fabrication.
arxiv pdf

Thermal reconstruction as a method of substrate preparation for highly crystalline superconducting TiN resonators

  1. Thomas J. Smart,
  2. Marc Neis,
  3. Janine Lorenz,
  4. Marcello P. Guardascione,
  5. Roudy Hanna,
  6. Michael Schleenvoigt,
  7. Yuan Gao,
  8. Joscha Domnick,
  9. Benjamin Bennemann,
  10. Abdur Rehman Jalil,
  11. Jin Hee Bae,
  12. Harsh Bhardwaj,
  13. F. Stefan Tautz,
  14. Felix Lüpke,
  15. Detlev Grützmacher,
  16. Rami Barends,
  17. Pavel A. Bushev,
  18. and Peter Schüffelgen
High quality crystalline growth of a thin film on sapphire requires sufficient substrate preparation, often achieved via the use of aggressive chemical cleaning. Direct thermal reconstruction
of the sapphire substrate via a CO2 laser beam may allow for an alternative way to prepare the substrate for epitaxy without the use of any chemical processing. Within this work, we demonstrate that thermal annealing of sapphire into its (31‾‾‾√×31‾‾‾√)R±9° reconstruction is a valid alternative preparation technique for sapphire substrates. TiN films grown via plasma-assisted molecular beam epitaxy upon these substrates exhibit greater crystallinity than those grown on chemically cleaned sapphire substrates. Superconducting resonators fabricated from these films exhibit similar performance, with many possessing internal quality factors at single photon levels greater than 106 for both substrate preparation methods.
arxiv pdf