SQUIDs (Superconducting QUantum-Interference-Devices) are the most sensitive sensors for magnetic fields. They make clever use of the properties, which are specific for superconductors: zero electrical resistance, expulsion of magnetic fields and quantization of magnetic flux.
Using a superconducting ring with a weak link (a Josephson contact) and a coupled rf-resonance circuit allows to detect changes of the magnetic flux which are smaller than 10-6 Phi0 (Phi0 denotes the magnetic flux quantum of 2*10-15 Tm2 or 2*10-7 Gauss cm2).
To get an idea of these changes are: The flux of the earth’s magnetic field through an area of 1 mm2 sums up to approx. 104 Phi0.
In order to operate a SQUID, the material has to be cooled below its critical temperature. Until 1986, the critical temperature of all known materials was pretty low and liquid helium had to be used for cooling. Unfortunately, liquid helium is expensive and difficult to handle. In 1986 so-called „High-TemperatureSuperconducting“ (HTS) materials were discovered by Müller and Bednorz. These materials can be cooled with cheap and easy-to-handle liquid nitrogen. Now SQUIDs may be used outside of research labs.
JSQ is offering „thin-film-rf-SQUIDs“ made from HTS materials. The design was developed at the Institute of Thin Film Technology at Research Center Jülich.
The thin films made from YBa2Cu3O7 are only 200 nm thick and are patterned onto ceramic substrates by photolithographic methods which are standard silicon processing technologies.