A superconducting bolometer with strong electrothermal feedback

We present a theoretical analysis and experimental evaluation of a transition-edge superconducting bolometer for detecting infrared and millimeter waves. The superconducting film is voltage biased and the current is read by a superconducting quantum interference device ammeter. Strong electrothermal feedback maintains the sensor temperature within the transition, gives a current responsivity that is simply the inverse of the bias voltage, and reduces the response time by several orders of magnitude below the intrinsic time constant C/G. We evaluated a voltage-biased bolometer that operates on the T-c similar to 95 mK transition of a tungsten film with a thermal conductance of G similar to 1.2 x 10(-9) W/K. As expected, the electrical noise equivalent power of 3.3 x 10(-17)/W root Hz is close to the thermal fluctuation noise limit and is lower than that of other technologies for these values of G and temperature. The measured time constant of 10 mu s is similar to 100 times faster than the intrinsic time constant. (C) 1996 American Institute of Physics.