A 1-MHz low noise preamlifier based on Double Relaxation Oscillation SQUIDs

A low noise and wideband preamplifier based on Double Relaxation Oscillation Superconducting Quantum Interference Devices (DROSs) has been realized. A major advantage of a DROS is that it can be operated in a simple flux modulation. So far, biomagnetic measurements performed in our group required only a limited bandwidth smaller than 100 kHz. Other applications, like for instance readout of radiation and particle detectors, demand a larger bandwidth. In this paper, we will discuss our efforts aimed at increasing the operational bandwidth of a DROS in flux locked loop. Presently, a flux locked loop scheme with a -3 dB bandwidth of 1.45 MHz has been built. With this system a white flux noise of 8 ¿¿0/¿Hz was measured with a 1/f-corner frequency of 10 Hz. The slew rate was 2.5·105 ¿0/s. With the mutual input inductance of 6.7 nH, an input current noise of the preamplifier of 2.5 pA/¿Hz was found and a current slew rate of 80 mA/s. We will discuss the suitability of our DROS-based preamplifier for readout of cryogenic particle detectors based on superconducting tunnel junction

Readout of cryogenic particle detectors based on Nb/Al-AlOx/Al/Nb Josephson junctions using double relaxation oscillation SQUIDs

A Double Relaxation Oscillation SQUID has been operated in a wideband flux locked loop system. The first measurements show a bandwidth of 1 MHz and a slew rate of 2.5-105 Φ0/s in combination with a white flux noise level of 8 µΦ0/√Hz. his corresponds to an input current noise of our DROS based current sensor of 2.5 pA/√Hz and a slew rate of about 0.08 A/s. The white noise level is still somewhat larger than the typical value of 2 pA/√Hz obtained in a 100 kHz bandwidth. Further developments are necessary to increase the slew rate and the bandwidth to make a DROS suitable for current readout of particle detectors based on superconducting Nb/Al-AlOx/Al/Nb tunnel junctions