Superconducting tunnel junctions as well as transition edge thermomete
rs could benefit from high quality thin films. We point out the import
ant features of various cryo detectors and show where high purity, or
even epitaxially grown films are advantageous for detector performance
. Some fabrication methods are discussed and methods of film character
ization introduced. Photolithography has proven necessary to fabricate
the complex structure of the present cryo detectors.