ゲルマニウム蒸着膜感温素子の低温における特性

抄録

Germanium thin films as resistance thermometers have been tested at liquid helium temperature. Germanium is deposited in vacuum on insulated substrates and then silver onto the germanium films as ohmic contacts. The thermometers with desired resistances and suitable sensitivities can be easily fabricated by choosing proper deposition conditions. The purpose of this work is to develop a thermometer with a fast response time for heat transfer experiments in liquid helium.
The characteristics of a typical thermometer are as follows. The film resistance can be expressed as a function of temperature by a simple correlation, logR=C+mlogT, between 4.2K and 20K. The sensitivity is approximately 20Ω/K. After 50 thermal cyclings, the increase rate of the resistance at liquid helium temperature is within 0, 8%. An estimated heat capacity of the film is 2×10^-8J/K, and a thermal relaxation time is of the order of 10^-12s at 4.2K.
These results prove that the germanium thin film thermometers are promising to measure transient surface temperature near 4.2K.
A stainless steel foil with the thermometers is heated by a direct current in a liquid helium bath, and the surface temperature of the foil are measured. Large temperature fluctuations due to occasional liquid solid contacts are observed.