Alberto Ronzani

Thermal resistance in superconducting flip-chip assemblies

  1. Joel Hätinen,
  2. Emma Mykkänen,
  3. Klaara Viisanen,
  4. Alberto Ronzani,
  5. Antti Kemppinen,
  6. Lassi Lehtisyrjä,
  7. Janne S. Lehtinen,
  8. and Mika Prunnila
Cryogenic microsystems that utilize different 3D integration techniques are being actively developed, e.g., for the needs of quantum technologies. 3D integration can introduce opportunities
and challenges to the thermal management of low temperature devices. In this work, we investigate sub-1 K inter-chip thermal resistance of a flip-chip bonded assembly, where two silicon chips are interconnected by indium bumps by atmospheric thermocompression bonding. The temperature dependence of the inter-chip thermal resistance follows the power law of αT−3, with α=7.7−15.4 K4 μm2/nW and a thermal contact area of 0.306 mm2. The T−3 relation indicates phononic interfacial thermal resistance, which is supported by the vanishing electrical thermal conduction due to the superconducting interconnections. Such a thermal resistance value can introduce a thermalization bottleneck, which can be detrimental for some applications, but it can also be harnessed. We provide a study of the latter case by simulating the performance of solid-state junction microrefrigerator where we use the measured thermal resistance value.
arxiv pdf

Characterizing Low-Quality-Factor Dissipative Superconducting Resonators

  1. Yu-Cheng Chang,
  2. Bayan Karimi,
  3. Jorden Senior,
  4. Alberto Ronzani,
  5. Joonas T. Peltonen,
  6. Hsi-Sheng Goan,
  7. Chii-Dong Chen,
  8. and Jukka P. Pekola
Characterizing superconducting microwave resonators with highly dissipative elements is a technical challenge, but a requirement for implementing and understanding the operation of
hybrid quantum devices involving dissipative elements, e.g. for thermal engineering and detection. We present experiments on λ/4 superconducting niobium coplanar waveguide (CPW) resonators, shunted at the antinode by a dissipative copper microstrip via aluminium leads, yielding a quality factor unresolvable from the typical microwave environment. By measuring the transmission both above and below this transition, we are able to isolate the resonance. We then experimentally verify this method with copper microstrips of increasing thicknesses, from 50 nm to 150 nm, and measure quality factors in the range of 10∼67 in a consistent way.
arxiv pdf