Static and radio frequency magnetic response of high T c superconducting quantum interference filters made by ion irradiation

Abstract

Abstract Superconducting quantum interference filters (SQIF) are promising devices for radio frequency (RF) detection combining low noise, high sensitivity, large dynamic range and wide-band capabilities. Impressive progress has been made recently in the field, with SQIF based antennas and amplifiers showing interesting properties in the GHz range using the well-established Nb/AlO x technology. The possibility to extend these results to high temperature superconductors (HTS) is still open, and different techniques to fabricate HTS SQIFs compete to make RF devices. We report on the DC and RF response of a high temperature SQIF fabricated by the ion irradiation technique. It is made up of 1000 superconducting quantum interference devices in series, with loop areas randomly distributed between 6 and 60 μ m 2 . The DC transfer factor is ∼450 V T −1 at optimal bias and temperature, and the maximum voltage swing ∼2.5 mV. We show that such a SQIF detects RF signals up to 150 MHz. It presents linear characteristics for RF power spanning more than five decades, and non-linearities develop beyond P RF = −35 dBm in our set-up configuration. The second harmonic generation has been shown to be at a minimum at the functioning point in the whole range of frequencies. A model has been developed which captures the essential features of the SQIF RF response.