A NEW TEMPERATURE SENSOR IN LOW-TEMPERATURE COMPOSITE BOLOMETERS FOR HIGH-RESOLUTION SPECTROSCOPY OF NUCLEAR RADIATION

We suggest a new type of temperature sensor in low temperature composite bolometers for detection of nuclear radiation. The new sensor is a two-dimensional (2D) array of ultrasmall (approximately 0.01mum2) aluminum Josephson junctions, situated on a micro machined silicon absorber. The incident radiation creates phonons in the absorber, which in turn can excite either charge solitons or vortex solitons in the 2D array. The benefit of this sensor is the low operation temperature, which is determined by the activation energy for the solitons, and can easily be as low as 20 mK. A low operation temperature is essential since the specific heat of the absorber has a T3 dependence. The activation energy can be set to the desired value by changing the individual junction sizes as well as the junction resistances. Furthermore, the optimal operation point may be trimmed by a moderate magnetic field. Since the atomic mass of aluminum is very close to that of silicon the Kapitza resistance between the absorber and the sensor is small. By keeping the aluminum electrodes in the superconducting state, the amount of additional electronic heat capacity from the sensor may also be kept low.