Microwave rf SQUID integrated into a planar YBa2Cu3O7 resonator

Abstract

We fabricated and characterized microwave rf SQUIDs integrated into a planar, S-shaped λ/2 microstrip resonator. This 3 GHz resonator was fabricated from a pulsed-laser-deposited YBa2Cu3O7 epitaxial film. The SQUID structures incorporated double step-edge junctions and had a loop inductance of 120 pH. Such unoptimized SQUIDs operated between 4.2 and 85 K with dV/dΦ=18–20 μV/Φ0 at 77 K. At that temperature, the energy resolution of (8±2)×10−29 J/Hz above 0.1 Hz (in the best samples) was limited by the white noise, SΦ1/2=(7±1)×10−5 Φ0/Hz1/2. Optimization may increase dV/dΦ and improve the energy resolution by up to an order of magnitude.

Squid Fundamentals

“…Configuration of microwave SQUID resonator with 100xlOO~m2 hole (re-drawn from ref. [142]). patterned to contain a l00xl00 ~m2 hole with two step-edge junctions along one edge; subsequently, the SQUID area was reduced to lOxl00 ~m2, with the longer side parallel to the edge of the resonator.…”

“…Several groups have successfully made rf SQUIDs that operate at 17K; of these, the most sensitive are those of the Jiilich group [65,141,142], which I briefly describe.…”

Magnetoencephalography using high temperature rf SQUIDs

“…Indeed, we have already demonstrated a very simple planar microwave rf SQUID operating at 3 GHz with Ls = 125 pH. This unoptimized device had, at a white noise level of 8 x 10 -29 J/Hz, slightly higher than that of our best 150 MHz SQUID, the crossover to 1/f noise near 0.01 Hz (Zhang et al 1992c). Naturally, the HTS dc SQUIDs with realistic inductances and well coupled integrated flux transformers may eventually attain sensitivities similar to that projected for an optimized microwave SQUID.…”

Microwave performance of YBa/sub 2/Cu/sub 3/O/sub 7-x/ resonators coupled to single-junction SQUIDs

“…(2) The SQUID loops were arranged parallel to the resonator section at the same position as in layout (1) but without galvanic contact ("indirect" coupling). The 3rd and 4th layout were analogous to (1) and (2) but had integrated flux focussing strips into which the SQUID loops were embedded [4].…”

“…The tank circuit was pattemed as a folded ("S"-shaped) half-wavelength microstrip resonator being resonant at 3 GHz [4]. Four different layouts were investigated: (1) The SQUID loops were galvanically integrated into the resonator near the expected HF current maximum of the fundamental mode ("direct" coupling).…”