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 composi te bolometers for detection of nuclear radiation. The new sensor is a two-dimensional (2D) array of ultrasmall (approximately 0.01mum2) alum inum Josephson junctions, situated on a micro machined silicon absorbe r. The incident radiation creates phonons in the absorber, which in tu rn can excite either charge solitons or vortex solitons in the 2D arra y. The benefit of this sensor is the low operation temperature, which is determined by the activation energy for the solitons, and can easil y be as low as 20 mK. A low operation temperature is essential since t he specific heat of the absorber has a T3 dependence. The activation e nergy can be set to the desired value by changing the individual junct ion sizes as well as the junction resistances. Furthermore, the optima l operation point may be trimmed by a moderate magnetic field. Since t he atomic mass of aluminum is very close to that of silicon the Kapitz a resistance between the absorber and the sensor is small. By keeping the aluminum electrodes in the superconducting state, the amount of ad ditional electronic heat capacity from the sensor may also be kept low .