A high stability temperature controller based on a superconducting high-T/sub c/ sensor

An analysis is given of a temperature control scheme described previously (1995), showing its intrinsic noise limitations. This scheme made good use of YBCO microbridges as temperature sensors. We find that high temperature to voltage transfer coefficient values (/spl Gt/1 V/K) are required in order to reach fluctuation levels well below 100 /spl mu/K/sub pp/. Consequently, a new design of the circuit has been made by introducing a current pre-biasing technique of the microbridge and allowing very large offset compensations. A transfer coefficient value of 441 V/K was used to obtain a temperature control with fluctuations less than 1.6 /spl mu/K/sub pp/ over a 2 hour recording time. Such high stability temperature controllers leading to fluctuation levels in the /spl mu/K/sub p/ range can prove to be very useful for high-T/sub c/ SQUID systems working at 77 K and in high-T/sub c/ bolometer applications.