Images of fabricated Devices

Conventional lithography techniques allow the patterning of Integrated Circuits (IC's) upon a substrate material. This picture shows a device patterned from YBCO which was subsequently used to produce and investigate the properties of sub-micron superconducting bridges. The square pads around the edge of th substrate are used to make contact between the sample and the measurement apparatus. The size of the substrate in this image is 5mm x 5mm.

The bridges shown in the picture above, patterned using photolithography, were analysed using an SEM. The wet-etching damage to the edge of the structure can clearly be seen. The bridge selected for further processing is 5microns wide, which gives an idea of the limitations of photolithography.

The same bridge is 'thinned down' using a Focussed Ion Beam (FIB) milling microscope. The etch damage is removed and the edges are much smoother. With this increase in quality, the bridge can be made much smaller.

A second mill of the bridge produces an even finer structure. The final bridge is 500nm wide and a few microns in length. The physics of such bridges is interesting as their superconducting properties change from the macroscopic to the quantum regime.

An even smaller bridge (approx 200nm wide) produced by the same technique. The results from these bridges are reproducible and the quality of the bridges is under investigation within the group.

The above image shows a different device geometry (cross geometry) where layers of different materials are patterned independently to form crossing tracks. Under an SEM it is clear that the deposition process for the materiqal crossing horizontally has not been optimised, as the film is of poor quality. By using the FIB technique, the area within which the materials cross can be minimised and the physics of the junction as a function of size can be investigated. Traditionally this has been one of the most interesting and yet difficult variables to adjust in a device measurement.

This image shows a photolithographic stage of device production. The first layer of material has been deposited an dpatterned, and the entire substrate coated with a second material. The photoresist covering this second layer of Gold and Niobium has been developed and the device begins to take shape.

The completed device after etching away the unwanted parts of the Gold and Niobium layers. This device was used in Spin Injection measurements.

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