Title :
Ultralow temperature SQUIDs for primary thermometry
Author :
Thomasson, S.L. ; Gould, C.M.
Author_Institution :
Dept. of Phys. & Astron., Univ. of Southern California, Los Angeles, CA, USA
fDate :
6/1/1999 12:00:00 AM
Abstract :
We have designed and constructed a primary thermometry system for operation from 4.2 K to temperatures well below 0.65 K, the bottom of the International Temperature Scale (ITS-90). The system is composed of a thin-film resistive-SQUID (R-SQUID) and a dc SQUID readout amplifier fully integrated on a single chip. We have fabricated our SQUIDs using Ti/Pd/Au shunt resistors, which remain normal conductive down to mK temperatures. Thermal and electrical constraints demand that the readout amplifier to the R-SQUID has a low system noise. We used a dc SQUID series array in a direct readout flux-locked loop scheme to achieve a system bandwidth in excess of 1 MHz with a white noise level less than 1 /spl mu//spl Phi//sub 0///spl radic/Hz.
Keywords :
SQUIDs; low-temperature techniques; resistance thermometers; superconducting device noise; superconducting thin films; temperature scales; white noise; 0.65 to 4.2 K; ITS-90; International Temperature Scale; Ti-Pd-Au; dc SQUID readout amplifier; electrical constraints; flux-locked loop scheme; primary thermometry; shunt resistors; system bandwidth; thermal constraints; thin-film resistive-SQUID; ultralow temperature SQUIDs; white noise level; Bandwidth; Circuit noise; Electrical resistance measurement; Low-noise amplifiers; Noise measurement; Resistors; SQUIDs; Temperature measurement; Temperature sensors; Voltage;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
