Superconducting kinetic inductance bolometer

The authors are developing a bolometer with a temperature sensor based on the temperature dependence of the inductance of a superconducting microstrip line. As a first step in exploring this idea experimentally, they have designed experiments to test only the temperature sensor. The experimental devices are all-niobium inductance thermometers fabricated on silicon substrates which have been deeply etched to provide areas of relative thermal isolation. The ground plane superconductor is thin enough so that its kinetic inductance dominates the audio frequency impedance of the stripline near its critical temperature, at 0.9 T_c. This differential thermometer uses a commercial SQUID (superconducting quantum interference device) as the preamplifier. Preliminary results demonstrate a proof-of-principle for the thermometer design. An important quality factor for this type of measurement system is the depth of the null. The authors achieved a high value of 0.4×10^-6, which is satisfying for a first try