Pulsed Laser Deposition: Future Directions
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make the process so unique, and that are discussed throughout this issue, are recapped below: 1. Rather complex multi-elementary materials can be deposited well if a single-phase, homogeneous target can be fabricated. The complexity of the deposition process is translated to the relatively easier process of fabricating a high-quality target. 2. The chamber pressure, target-substrate distance, target orientation with respect to the laser beam, etc. are significantly decoupled, enabling significant freedom in deposition system design. The target is decoupled from the substrate in the sense that a small target can be used to deposit film over a fairly large area substrate with the appropriate scanning schemes. 3. The efficiency of the target use is superior compared to any other technique since a predominant amount of the evaporated
Table 1. Partial List of Metal-Oxides of Commercial Importance. Property High optical transparency Low-loss dielectric with electrooptic effect
Metal-Oxide System MgO, ZrO LiNbO3, LiTaO3
Piezoelectricity Ferromagnetism
BaTlO3, PuTlo.46ZrQ5403
Optical nonlinearity
Nb 2 O5-SiO2-Na2O-Ba 2 O3-TiO2
High optical gain Transparent conductors
N d 3 + doped Y3AI5O12
Superconductivity
Y-Ba-Cu-O, TI-Ba-Ca-Cu-0
54
y-F©203
InSnO,,
Application Mirror coatings Optical wave guides and integrated optics Transducers Magnetic tape memories All optical switching devices Lasers Novel device coatings SQUIDs Superconducting electronics
material is forward directed and can be collected with a high degree of efficiency. For example, in a production environment, more than 100 YBCO films (ranging 3,000-4,000 A thick) on 1 X 1 cm2 substrates have been fabricated from a 0.25inch-thick one-inch target with a majority of the target still left over.6 The cost of raw materials in a production environment may become significant, and for toxic elements particularly there is a further advantage in minimizing the spread of contaminants.7 4. The forward directed evaporant in this process lends itself to novel substrate handling schemes such as the recessed black body heater, to be described later, which may not be possible, for instance, with most sputtering techniques. 5. The fabrication of multilayers is fairly straightforward, with rapid substitution of targets into the path of the laser beam. Most materials have a common range of evaporation parameters. Hence it is relatively easy to design automated systems capable of rather sophisticated thin film structures. Some of the most complex integrated high Tc components were demonstrated recently using pulsed laser deposition.8
Materials Base The concerted effort in developing insitu processes to deposit high-temperature superconductors and associated dielectric and buffer layers has given us the confidence to extend this technique to other materials. Such an effort has already begun, and Table I summarizes diverse areas that could benefit from this process. While this table summarizes the technologically important metal oxides only, it is fairly easy to imagine
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