Design and implementation of a dual-control active device using YBCO grain-boundary junctions

We propose a dual-control active device based on overdamped long junctions. In analogy to the semiconductor dual-gate field effect transistor which can be considered a cascode (output terminals in series) of two single-gate FETs, the dual-control device consists of two single devices in parallel at the outputs. The transresistance of one device is shown to be a linear function of the second control current over a sizable range. This unique feature makes the dual-control device highly desirable for applications such as gain control and mixing, Active devices have been fabricated using arrays of YBCO bi-crystal grain-boundary junctions. Tight coupling of the control fields to the array was achieved by injecting the control current into an "ear" structure at one end of the array. The large-signal current gain, however, is less than 1 due to the asymmetric bias and end injection. Improved current gain with tight coupling to the entire array is necessary for a practical dual-control device.