Extensible quantum computing architectures require a large array of quantum devices operating with low error rates. A quantum processor based on superconducting quantum bits can be scaled up by stacking microchips that each perform different computational functions. In this article, we experimentally demonstrate a thermocompression bonding technology that utilizes indium films as a welding agent to attach pairs of lithographically-patterned chips. We perform chip-to-chip indium bonding in vacuum at 190∘C with indium film thicknesses of 150nm. We characterize the dc and microwave performance of bonded devices at room and cryogenic temperatures. At 10mK, we find a dc bond resistance of 515nΩmm2. Additionally, we show minimal microwave reflections and good transmission up to 6.8GHz in a tunnel-capped, bonded device as compared to a similar uncapped device. As a proof of concept, we fabricate and measure a set of tunnel-capped superconducting resonators, demonstrating that our bonding technology can be used in quantum computing applications.
@article{arxiv.1705.02435,
title = {Thermocompression Bonding Technology for Multilayer Superconducting Quantum Circuits},
author = {C. R. H. McRae and J. H. Béjanin and Z. Pagel and A. O. Abdallah and T. G. McConkey and C. T. Earnest and J. R. Rinehart and M. Mariantoni},
journal= {arXiv preprint arXiv:1705.02435},
year = {2017}
}