Study of the magnetic coupling between a SQUID and wires integrated on a chip

Magnetic coupling between a SQUID and wires in an integrated circuit has been studied. Using test integrated circuits, the coupling is measured by varying the distance from the SQUID to each wire. The coupling between the SQUID and the wires with and without a groundplane decreases with an increase in the distance. The coupling for the wires with the groundplane is smaller than that for the wires without the groundplane at distances less than 595 /spl mu/m. However, the rate of the decrease in the coupling for the wires with the groundplane falls off for distances more than 595 /spl mu/m and the coupling converges to around 2.9 pH. From two dimensional simulations for the magnetic flux coupling, the origin of the residual inductance is found to be the coupling between the SQUID, and shielding current in the groundplane. The value of the distance, 595 /spl mu/m, does not depend on the size of the SQUID. To decrease the coupling, the use of wires with stripline structure or coplanar structure is desirable.