Behavior of diffused planar germanium thermometers at temperatures below 1 K

The performance of diffused planar germanium thermometers is found to be reliable at temperatures T>90 mK. At lower temperatures performance can be limited by overheating caused by measuring and spurious currents. The heating is associated with a thermal impedance Z∝T−4 which is larger than that found in typical bulk germanium thermometers. Surprisingly, Z is found to be essentially independent of the size of the planar resistor.