PHD RESEARCH WORK

SUPERCONDUCTING FLEXIBLE CABLES

For my Phd work I am working on superconducting flexible transmission lines with embedded traces, such as Stripline, embedded Microstrip and resonators. The main purpose of of builduing these cables is to minimize thermal load and space inside a cryogenic system. For this work we use flexible sustrates such as polyimide. Polyimide has been used for a long time as insulation and passivation layers in applications such as MEMS chips, stress buffers, flip chip and bond pad redistribution applications, since it exhibits excellent mechanical properties.Nb is major material we focus on as a superconductor.
As a part of my research I have investigated multiple material stack up to minimize degradation of Nb superconducting properties when subjected to high temperatures during subsequent fabrication processes, such as curing of passivating polyimide layer at 350˚C. A thin-layer of Al was used as a barrier layer since it did not degrade the high frequency signal propagation due to microwave skin effects or proximity effects. This experiment provided an insight into a possible material stack up for robust, multi-layer superconducting RF flexible cables that can be used in future cryogenic electronics systems. Some of the tools we use include HFSS, sonnet and advanced design system (ADS). HFSS and sonnet are essentially used to simulate the microwave response of the resonator, Microstrip and Stripline. ADS is used to design the layout of the device and to verify the microwave response. We test the RF and microwave performance of the fabricated devices at low temperature of the order of 1.2 K.
Densely integrated superconducting multi-layer and multi-signal flexible cables will be useful for the massive number of electrical interconnects in future superconducting and cryogenic electronic systems, including superconducting quantum computers and detector arrays. In addition to having a cost effective solution to cryogenics, flexible thin film interconnects have the potential of minimizing size and thermal leakage producing prominent signal transmission. 
The image on the right is the inside of a D-Wave two quantum computer housed at the NASA Advanced Superconducting facility.