Thomas R. Stevenson, "Microwave Kinetic Inductance Detectors for Astrophysics Applications"

Microwave Kinetic Inductance Detectors (MKIDs) detect absorption of photons with energy greater than the energy gap in a superconducting thin film, which is made part of a microwave resonator, as a change in kinetic inductance that shifts the resonance frequency. MKIDs have found application in a variety of current astrophysics instruments because of their high sensitivity and natural multiplexing capability. Two current examples of quite different MKID designs are those used in the NASA high altitude balloon-borne instruments for the Experiment for Large Aperture Intensity Mapping (EXCLAIM) and the Terahertz Intensity Mapper (TIM). In addition to the physics of generation and recombination of quasiparticles in superconductors, the sensitivity of MKIDs depends on minimizing noise from capacitance fluctuations from Two-Level-Systems in disordered dielectrics that are present in the resonator. At Goddard Space Flight Center, we have developed MKID designs that use single-crystal silicon as the principal dielectric, such as in EXCLAIM’s half-wave aluminum microstrip transmission line resonators, or in a photon-counting lumped element Al-NbTiN MKID approach. We have also recently reported on the performance of a novel, highly compact, three-dimensional microwave resonator design for Microwave Kinetic Inductance Detectors covering mid- and far-infrared wavelengths. Those “3D-MKIDs” are fabricated using deep-etched holes in a silicon substrate, coated internally with alternating layers of aluminum oxide and superconducting titanium nitride films formed by Atomic Layer Deposition (ALD). By bending part of the resonator into the third dimension, the optically absorptive area (the kinetic inductor) can occupy a greater fraction of the focal plane area.

Thomas Stevenson gained extensive experience in low temperature techniques and low noise measurements in the field of gravitational radiation detection. His doctoral research improved the experimental upper limit on radiation flux and produced a novel superconducting motion sensor. Continuing transducer research at the University of Maryland, he collaborated on developing dc SQUID amplifiers with nearly quantum-limited sensitivity. He served as Cryogenic Detectors group leader in the Detector Systems Branch at NASA Goddard 2004-2008, and as Associate Branch Head 2009-2010. Currently, he performs basic research on superconducting properties of materials and devices and develops detectors for space applications in the spectral range from x-ray to microwave.