High Sensitivity Thermometers for Millikelvin Temperature Range

Abstract

Commercial RuO2 — based thick film resistors (TFRs) were successfully introduced as low temperature thermometers in the last years [1, 2, 3, 4, 5, 6, 7, 8]. Their low magnetoresistance [1, 2, 3, 4, 5], possibility to predict their low temperature R–T behavior from room temperature resistance [5] and possibility to lower their heat capacity simply by shaving its alumina substrat without significant altering of the electrical properties [4,7] predict them as practical, easy-to-use and low cost thermometers, mainly in temperature range below 1K. Moreover, our earlier studies shown, that thermometers for milikelvin temperatures with high (comparable to germanium thermometers) sensitivities, sufficient stability and suitable resistance ranges may be prepared based on RuO2 thick films, if they are designed for this purpose and if suitable types of pastes for their preparation are used [8]. The all mentioned facts were motivation for us to try to develop improved RuO2 — based thermometers as alternative thermometers (in milikelvin temperature region) to germanium ones. During our research we found some technical limitations that may be interesting from both technical and physical point of wiew. The aim of this paper is a short description of them.