Superconducting submillimeter and millimeter wave detectors Page: 8 of 135
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boundary resistance between the YBCO film and the underlying substrate could possibly
account for many of the experimental observations. At first this did not seem likely since it
was well known that thermal boundary resistances, which scale as T-3, should be
negligible at these high temperatures. It quickly became clear to us however, that this may
not be the case in experiments involving fast laser pulses incident on thin films. We thus
embarked on a set of experiments to measure directly the magnitude of the thermal
boundary resistance between YBCO films and the underlying substrate.10
Having gained a solid understanding of antenna-coupled bolometers, and of thermal
boundary resistances, we then inquired whether a low-Tc microbolometer could compete
with conventional composite bolometers operated at and below 4.2 K. We came to the
conclusion that this approach could not only lead to an order of magnitude improvement in
sensitivity, but also that several of the obstacles associated with the development of array
systems could be overcome.11,12 Needless to say, we decided to pursue this approach.
We established a collaborative effort with Professor D. E. Prober's group at Yale
University in which the devices would be fabricated at Yale whereas all of the
measurements would be carried out at Berkeley.
We invented the hot-electron microbolometer a little less than a year prior to the writing
of this dissertation. Our initial estimates suggested that it could be possible to attain
approximately two orders of magnitude higher sensitivity than that of the best available
bolometers when operated at the same temperature.13 The hot-electron microbolometer
would thus be the most sensitive direct detector of submillimeter and millimeter waves, and
could potentially be the detector of choice in many applications which require very high
sensitivities and array compatibility. In addition, the readout scheme that we invented
could be used to measure the intrinsic interaction between electron and phonons in a metal
at low temperatures, with a much higher resolution than the conventional SQUID readout
method.14 Although these concepts have not been tested, I have decided to include the
analysis in this dissertation.2
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Nahum, M. Superconducting submillimeter and millimeter wave detectors, thesis or dissertation, October 20, 1992; California. (https://digital.library.unt.edu/ark:/67531/metadc1311365/m1/8/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.