Characterization of Photolithographically Microfabricated SIN Tunnel Junctions for X-Ray and Phonon Spectroscopy

A thesis submitted to the faculty of
San Francisco State University
in partial fulfillment of the
requirements for the

Master of Science


Daniel Tun Lai Chow

San Francisco, California

September, 1995


This thesis describes the fabrication and testing of Superconductor- Insulator-Normal (SIN) tunnel junctions for dark matter detection and x-ray spectroscopy.  Astrophysical evidence suggests that ~90% of the mass of the universe is undetectable by conventional means.  Theory suggests that this mass consists of weakly interacting massive particles (WIMPs).  Calculations show that WIMPs are most likely to interact with nuclei and create phonons in a large detector crystal.  SIN junctions can detect phonons from these nuclear recoils.  In x-ray astronomy, it is desired to have efficient, broad-band, and high energy resolution spectrometers.  Current spectrometers must sacrifice either resolution or efficiency.  SIN junctions coupled to a suitable absorber possess all the qualities necessary for x-ray spectroscopy.  The junctions are made by optical contact photolithography in the microfabrication facilities at SFSU.  They are characterized by testing down to 270mK at SFSU and 50mK at LLNL.  The SIN devices were found to be uniform and stable.  Junctions fabricated on silicon substrates possess an energy resolution better than 150eV at 6keV.