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TITANATE THIN FILMS BECOMING A REALITY WITH CRYSTAL ION SLICING
The recently developed method of crystal ion slicing (CIS) is rapidly gathering interest and attention as a novel way of successfully obtaining single-crystal thin films. The excellent opto-electrical properties of barium titanate, BaTiO3, make this ferroelectric crystal eminently suitable for applications such as capacitors, pyroelectric detectors, and nonlinear optics. These films possess high dielectric constants and large pyroelectric and nonlinear coefficients. However, many potential applications for barium titanate require a thin-film form rather than a bulk crystal. Despite substantial advances in deposition technologies for barium titanate thin films, researchers have faced continued difficulty in obtaining high-quality, single-crystal thin films, since they require lattice matching to the growth substrate. CIS looks set to offer researchers a solution to these problems. 'The CIS technique enables one to slice a 0.5 micrometers to 10 micrometers-thick layer of material from a bulk single-crystal wafer by implanting the wafer with high-energy ions and subsequent thermal treatment or wet etching of the buried sacrificial implant-damaged layer,' says Technical Insight Industry Manager Girish Solanki. Essentially, this technique uses ion implantation to modify the chemical and physical properties of materials and obtain mesoscopically thin, single-crystal films. Post ion slicing, researchers used sophisticated analytical tools such as atomic force microscopy (AFM) to examine the samples' surface roughness and domain structure. They observed a change in the wafers' domain structure from single to multidomain as well as a periodic structure in the surface topography. Using a near-field scanning microwave microscope (NSMM), researchers also noted that the barium titanate film retained the permittivity of the bulk crystal and exhibited low dielectric loss; they attributed the latter to stress induced by residual implanted ions and a thermal expansion mismatch between the substrate and the film. Observing the large permittivity of the sliced barium titanate films, researchers concluded that it was possible to fabricate a small-sized, large-capacitance, integrated capacitor on CIS single-crystal films. Commenting on the future of barium titanate, Solanki says, 'As far as practical areas of application are concerned, the heterogeneous integration of the material makes it possible to realize multi-functional microwave and optical devices. Barium titanate is also a promising material for memory applications.'
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