Relaxation oscillation SQUIDs with high delta V/ delta Phi

Abstract

Relaxation Oscillation SQUIDs (ROSs) based on Nb/Al,AlO,/AVNb Josephson tunnel junctions have been designed and fabricated. The hysteretic SQUIDs have a maximum critical current of about 130 pA and an inductance of 20 pH. A voltage modulation of 400 pV and a flux to voltage transfer SV/6@ of 4 mV/@, have been measured in these SQUIDs. Double Relaxation Oscillation SQUIDs (DROSs), which are based on two hysteretic SQUIDs, showed transfer coefficients up to 77 mV/@,. The intrinsic white flux noise of the DROSs is smaller than 3-5 p@JdHz. The results are very promising for a next generation of SQUID systems with simplified read-out.

High sensitivity double relaxation oscillation superconducting quantum interference devices

“…11-14 A DROS transforms an input flux to a voltage with a transfer coefficient that is two or three orders of magnitude larger than in comparable standard dc SQUIDs, which facilitates direct voltage readout. 15,16 In this letter, we will show that the intrinsic sensitivity of a DROS can be of the same order of magnitude as in comparable standard dc SQUIDS.…”

“…16,17 By adding an extra resistor R d parallel to the SQUID, these resonances can be damped. 14 The value of R d can be obtained from…”

The use of (Double) relaxation oscillation SQUIDs as a sensor

“…The width of the transition from V -0 to V = V,, and thus the flux-to-voltage transfer aV/a(r,, is determined by the thermal spread in the critical currents of both SQUIDs [5], [6]. In practice, aVla(r, is in the order of 1 mV/m0, as illustrated in the experimental V(@) characteristic of Fig.…”

“…Its contribution decreases for increasing relaxation frequencies, at relaxation frequencies in the order of 1 GHz, the theoretical sensitivity of a ROS is comparable to that of standard dc SQUIDS [6]. A more comprehensive description of the theoretic background of the ROS can be found in [4].…”

“…This large flux-to-voltage transfer enables FLL operation based on direct voltage readout, without flux modulation. As in the case of a ROS, the relaxation frequency of a DROS should be around 1 GHz for optimum sensitivity [SI, [6]. by damping of resonances in the input coil [7].…”