Plasma-enhanced atomic layer deposition of titanium nitride for superconducting devices

  1. John Femi-Oyetoro,
  2. Sasha Sypkens,
  3. Henry LeDuc,
  4. Matthew Dickie,
  5. Andrew Beyer,
  6. Peter Day,
  7. and Frank Greer
This study presents a comprehensive investigation into the exceptional superconducting attributes of titanium nitride (TiN) achieved through plasma-enhanced atomic layer deposition
(PEALD) on both planar and intricate three-dimensional (3D) structures. We introduced an additional substrate biasing cycle to densify the film and remove ligand residues, augmenting the properties while minimizing impurities. While reactive-sputtered TiN films exhibit high quality, our technique ensures superior uniformity by consistently maintaining a desired sheet resistance greater than 95 percent across a 6inch wafer, a critical aspect for fabricating extensive arrays of superconducting devices and optimizing wafer yield. Moreover, our films demonstrate exceptional similarity to conventional reactive-sputtered films, consistently reaching a critical temperature (Tc) of 4.35 K with a thickness of around 40 nm. This marks a notable achievement compared to previously reported ALD-based superconducting TiN. Using the same process as for planar films, we obtained Tc for aspect ratios (ARs) ranging from 2 to 40, observing a Tc of approximately 2 K for ARs between 2 and 10.5. We elucidate the mechanisms contributing to the limitations and degradation of superconducting properties over these aggressive 3D structures. Our results seamlessly align with both current and next-generation superconducting technologies, meeting stringent criteria for thin-film constraints, large-scale deposition, conformality, 3D integration schemes, and yield optimization.

Demonstration of a Quantum Noise Limited Traveling-Wave Parametric Amplifier

  1. Nikita Klimovich,
  2. Peter Day,
  3. Shibo Shu,
  4. Byeong Ho Eom,
  5. Jenry Leduc,
  6. and Andrew Beyer
Recent progress in quantum computing and the development of novel detector technologies for astrophysics is driving the need for high-gain, broadband, and quantum-limited amplifiers.
We present a purely traveling-wave parametric amplifier (TWPA) using an inverted NbTiN microstrip and amorphous Silicon dielectric. Through dispersion engineering, we are able to obtain 50 Ω impedance matching and suppress undesired parametric processes while phase matching the three-wave-mixing amplification across a large range of frequencies. The result is a broadband amplifier operating with 20 dB gain and quantum-limited noise performance at 20 mK. At the single frequency where the amplifier is phase sensitive, we further demonstrate 8 dB of vacuum noise squeezing.