Properties of zinc thin film thermometers

Thin films of aluminum have for many years been used near T similar to 1.5 K to detect the tiny temperature fluctuations which accompany the propagati on of waves of third sound in thin superfluid He-4 films. For lower tempera tures, zinc thermometers have been used to detect phonon propagation in bul k helium. We have fabricated zinc thermometers having zero-field sensitivit ies delta R/delta T similar to 20000 Ohm/K at T-c similar to 680 mK when op erated at a bias current i(b) = 10 mu A. We describe here the fabrication t echniques and the operating characteristics of thin film zinc thermometers which we have used to detect third sound for 100 less than or equal to T le ss than or equal to 680 mK. (C) 2000 Elsevier Science B.V. All rights reser ved.