SQUID current amplifiers for sub-kelvin operation temperatures Original Research Article

Extremely sensitive current sensors are being developed by integrating input coils on superconducting quantum interference devices (SQUIDs) and optimizing them for being cooled to the mK temperature range. The most important effects for this type of sensors are investigated in this paper. SQUID characteristics were experimentally studied at mK temperatures and in numerical simulations, revealing a crucial hysteretic effect originating from parasitic elements introduced by the integrated coil. Furthermore, the cooling behavior of shunt resistors with attached cooling fins, dominated by the hot-electron effect, was investigated. A numerical model allows to reproduce the experimental data in a good way.