The Effect of Magnetic Nanoparticles on Inductances for SFQ Device Application

Abstract

The use of magnetic material can improve the performance of a single-flux-quantum device by inducing high self-or mutual inductance, which can reduce the size or increase the sensitivity of the device. We used magnetic nanoparticles as the magnetic material and adopted photoresist patterns with Fe 3 O 4 nanoparticles as a means of inserting nanoparticles into a device. The effect of the nanoparticles was investigated for SQUIDs with photoresist patterns. Analytical estimation of the effect indicated a variation in SQUID inductance of less than 1%, which is in agreement with the experimental results in the absence of external magnetic fields. On the other hand, when external DC magnetic fields were applied, a slight increase in inductance was observed for several SQUIDs.

Effects of magnetic nanoparticle films on the electrical characteristics of dc superconducting quantum interference devices

“…First, we fabricated dc-SQUIDs in a washer configuration on a Si substrate using a Nb/AlO x /Nb junction fabrication process, as reported previously. 14) The film thicknesses were 200 nm for the upper and lower Nb electrodes, 350 nm for the SiO 2 insulating layer, and 450 nm for the upper wiring layer. Each SQUID was shaped like a square washer with a conductor width of 26 µm and a 7 © 7 µm 2 hole.…”

“…To eliminate these difficulties, we have been studying the insertion of high-permeability magnetic materials into SFQ circuits. 14) The use of magnetic materials can compensate for the reduced sheet inductance of inductors. In addition, their use can increase the coupling factor, which determines mutual inductance.…”

“…Previously, we used photoresists with Fe 3 O 4 NPs, which can easily be patterned by conventional photolithography. 14) First, we estimated the magnetic effects of the photoresist patterns on the inductance of superconducting quantum interference devices (SQUIDs) and studied their effects experimentally. No clear effects were observed, owing to the small proportion of NPs relative to the volume of the photoresist.…”

Cryogenic ferromagnetic patterns with controlled magnetization for superconducting phase-shift elements

“…The PdNi films were easily patterned to micron-or submicron-scale, compared with the nanoparticle films used in our previous studies. 18,19) To evaluate the effects of the PSE, rectangular tunnel junctions, with PdNi patterns placed at the same height as the junction barrier, were fabricated and tested. Josephson junctions were used to measure the amount of flux induced by the cryogenic ferromagnetic patterns; the flux was determined from the horizontal shift of the main lobe in the I c modulation pattern for the external magnetic field.…”

High-frequency characteristics of dc-SQUIDs with magnetic nanoparticle patterns

“…First of all, we focused on magnetic nanoparticles (NPs), because the NPs show the magnetic properties depending on their diameters, which results in convenience for us to use [5]. We observed clear effects of Fe 3 O 4 NP film patterns on the static characteristics or magnetic field modulation of the SQUIDs [6].…”