Superconducting flux-flow transistors based upon YBa/sub 2/Cu/sub 3/O/sub 7/ nanobridges

Superconducting flux-flow transistors were fabricated from thin (50 nm) high temperature superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ films. In order to determine whether the suppression of the critical current by an applied control current is caused by the magnetic induction or thermal heating due to dissipation in the control line, two different device geometries were developed. The first structure consists of a parallel array of short nanobridges and one parallel control line. In the second structure, a single 10 /spl mu/m long nanobridge is arranged with two parallel long control lines placed on both sides of the signal line. Our measurements demonstrate that in both geometries the magnetic induction of the control lines suppresses the transport properties of the nanobridges. However, for control currents larger than the critical current the transport properties of the bridge are additionally strongly suppressed by thermal effects, which are caused by heating of the current-biased control lines. Furthermore, transistor structures with one long nanobridge and two control lines react more sensitively to small control currents than the device with a single and short control line. They can operate at currents far below the critical current, which leads testable transistor devices.<
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