| Summary: | This thesis was motivated by the suggestion that selectively implanting YBa₂Cu₃0₇
(YBCO) films with a highly reactive ion, such as Si, could pattern without destroying or
removing material. If true, this would greatly simplify conventional methods of patterning
multilayer structures. This led to systematic studies on the use of ion implantation
to pattern YBCO thin films and multilayers.
The samples used were obtained by developing a method referred to as scanning
pulsed laser deposition. This technique resulted in the reproducible growth of highly
crystalline YBCO thin films with high transition temperatures and critical currents.
A study of Si implantation was first done to elucidate the exact mechanism by which
it rendered YBCO non-superconducting. Measurements of films implanted at various
energies and doses revealed that implantation at required doses severely damaged the
films crystalline structure, destroying superconductivity.
The growth of high quality multilayers require that the underlying patterned film
retain its as-grown crystalline quality. A damaged film can regain that quality (to some
extent) with high temperature annealing. Measurements of annealed implanted films
revealed that crystalline damage at levels >10 displacements per atom (dpa) could not
be completely removed at accessible annealing temperatures. However, when the implantation
damage was kept below 1-2 dpa, an annealing temperature of ~ 900°C was
successful in recovering most of the original structure. Unfortunately, at these temperatures,
the Si-implanted film phase separated, forming islands of a Si-mixed material in a
sea of YBCO , and thus regained its original high transition temperature.
To address the original claims that Si implantation would not destroy the film, a
film was rendered non-superconducting with the appearance that it maintained its crystallinity
by implanting only near the films surface. In this case, the film was effectively
passivated and a low temperature anneal resulted in oxygen leaving the underlying YBCO
structure to the more energetically favored Si0₂ states in the implanted layer. Replenishment
of oxygen from the atmosphere was hindered due to the passivating layer capping
the film.
Patterning films by implanting Si was thus deemed to be unsuitable for multilayer
structures.
A new technique of substitutional ion implantation patterning was developed using
Mg ions. Mg substitutes for the Cu in the Cu-0 planes, drastically reducing transition
temperature with very low concentrations. The low required concentrations allowed
the use of low implant doses. This, coupled with the relatively low mass of the Mg
ion, reduced the implantation damage to levels easily removed with high temperature
annealing. As well, the high temperature anneal can incorporate Mg into the YBCO
matrix, forming the compound, YBa₂(Cu₁[sub -x]Mg[sub x])₃0₇. The process of implanting Mg
into YBCO , followed by a high temperature anneal resulted in the formation of a highly
crystalline, non-superconducting material at 77K. Mg implantation was used to successfully
pattern films with a resolution of 10 μm. Bilayers with a top YBCO layer and a
bottom YBa₂(Cu₁[sub -x]Mg[sub x])₃0₇ were fabricated. Resistivity and x-ray measurements reveal
the high quality of both layers. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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