The developments over the last decade in Focused Ion Beam (FIB) instrument
technology have reached a point where there is sufficient control of an ion beam to make
cuts, trenches, and other shapes in a sample on a scale of tens of nanometers. This work
concentrates on the use of an FIB instrument for making superconducting devices. It is
shown for the first time that planar-bridge (Nb/Cu/Nb) Superconductor/Normalmetal/
Superconductor (SNS) junctions can be reliably fabricated using a standard FIB
instrument. This is demonstrated by the responses of junctions to microwaves and magnetic
fields; the junctions display the appropriate Josephson behaviour demanded by current
technological applications. In addition, the reproducibility in junction behaviour (the
variation of critical current is approximately 10%) is the best so far observed for this type of
junction. The SNS junction fabrication method has been successfully extended for making
high-density SNS junction arrays, dc-SQUIDs, and related devices. A simple model is
devised to explain the normal-state resistance and critical current of a junction. The model is
based on the geometry of a junction as defined by the FIB instrument and the film
deposition. The model is mostly successful in qualitatively explaining many of the
geometrical factors that affect the electrical properties of the junction. Nb/Cu/Nb junction
series arrays, made using an FIB instrument, are also successfully fabricated. The yield of
the junctions forming small arrays is found to be similar to the yield of single junctions. For
the series arrays studied here, new observations have been made: the electrical properties of
an array have been found to be dependent on the spacing of the junctions and the number of
junctions in the array.
This work also investigates the thermal properties of SNS and micron-scale
superconductor/insulator/normal-metal junction based devices for use in bolometer device
based applications. It is shown that self-heating raises the temperature of the junctions
significantly above their operating temperatures. For a device sitting on a low thermally
conductive membrane, it is found that the effects of heating, or cooling, in the junctions are
exaggerated