Ultralow temperature SQUIDs for primary thermometry

• Published in: IEEE transactions on applied superconductivity Vol. 9; no. 2; pp. 3507 - 3510
• Main Authors: Thomasson, S.L., Gould, C.M.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.06.1999; Institute of Electrical and Electronics Engineers
• Subjects: Amplifiers; Applied sciences; Arrays; Bandwidth; Circuit noise; Demand; Direct current; Electrical resistance measurement; Electronics; Exact sciences and technology; Low-noise amplifiers; Noise measurement; Palladium; Resistors; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; SQUIDs; Superconducting devices; Superconducting quantum interference devices; Temperature measurement; Temperature sensors; Titanium; Voltage; Thin film device; Voltage current curve; Manufacturing process; Superconducting quantum interferometer device; Thermometry; White noise; System design; Transfer function; Chip; Noise level
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/77.783786

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.