The problem of electromechanical film characterization, and, in particular, the determination of the piezoelectric activities of thin films deposited on substrates, is of fundamental importance in the development of structures for microelectromechanical system (MEMS) applications. The design and the architecture of the piezoelectric MEMS are directly related to the mechanical and the piezoelectric performances of the material. In this article, we present and compare some results obtained on different experimental setup for the determination of the $d_{33}$ coefficient. We have optimized the experimental conditions using a laser Doppler vibrometer. The main problem is the contribution of the bending effect of the substrates on the $d_{33}$ coefficient, which is an intrinsic property of the film. We show that the $d_{33}$ values are directly related to parameters such as the top electrode diameter and the substrate holder. The results are in agreement with those obtained with the conventional double beam interferometer used to account for substrate bending.

Brillouin light scattering, Raman light scattering and x-ray diffraction were used to investigate the elastic and microstructural properties of polycrystalline and smooth fine-grained diamond films of varying diamond quality. They were deposited on a titanium alloy by a two-step microwave plasma-assisted chemical vapor deposition process at 600 °C. Their morphology and roughness were studied by scanning electron microscopy and atomic force microscopy. Their refractive indices were determined by the M-line spectroscopy technique. The diamond purity of all these coatings in terms of the ${\mathrm{sp}}^3$ bonding fraction was deduced from visible and UV Raman spectroscopy as a function of the deposition conditions. All the samples were found to be textured with a 〈011〉 crystallographic direction normal to the film plane, leading to essentially hexagonal symmetry of the elastic tensor. By taking advantage of the detection of a number of different acoustic modes, complete elastic characterization of the films was achieved. The elastic constants $C_{11}$ and $C_{66},$ respectively, were selectively determined from the frequency of the longitudinal and shear horizontal bulk modes traveling parallel to the film surface. The three remaining elastic constants, namely, $C_{44},$ $C_{33}$ and $C_{13},$ were obtained from detection of the Rayleigh surface wave a bulk shear wave and the bulk longitudinal wave propagating at different angles from the normal to the surface. The values of the elastic constants depend on the deposition conditions and on the microstructural properties of the films, especially the diamond quality and the polycrystalline or smooth fine-grained nature of the diamond. For the polycrystalline diamond film with the best quality, the elastic constants are rather close to the Voigt or Reuss average estimate values using known bulk elastic constants of diamond, whereas those of the smooth fine-grained diamond films are reduced because of the poorer diamond quality leading to lower residual stress in the films.

Lithium niobate’s use in integrated optics is somewhat hampered by the lack of a capability to create low loss waveguides with strong lateral index confinement. Thin film single crystal lithium niobate is a promising platform for future applications in integrated optics due to the availability of a strong electro-optic effect in this material coupled with the possibility of strong vertical index confinement. However, sidewalls of etched waveguides are typically rough in most etching procedures, exacerbating propagation losses. In this paper, we propose a fabrication method that creates significantly smoother ridge waveguides. This involves argon ion milling and subsequent gas clustered ion beam smoothening. We have fabricated and characterized ultra-low loss waveguides with this technique, with propagation losses as low as 0.3 dB/cm at 1.55 µm.

We present the results of investigations of lithium niobate $({\mathrm{LiNbO}}_{\mathrm{3}})$ films grown on (0001) sapphire substrate by radio-frequency magnetron sputtering. With the aim of producing thick films we have developed a multistep process. To assess the structural quality of our films, we performed x-ray diffraction, transmission electron microscopy, and atomic force microscopy of the films. The results revealed that the epitaxial structure is verified on sapphire whatever the film thickness. Based on our studies we concluded that the proposed multistep process leads to a good controlled epitaxy of thick ${\mathrm{LiNbO}}_{\mathrm{3}}$ samples on sapphire. Using the prism coupling technique we have characterized the optical properties of the deposited layers. The ordinary ${\mathrm{(n}}_o)$ and extraordinary ${\mathrm{(n}}_e)$ refractive indices are, respectively, $\text{2.289±0.001}$ and $\text{2.206±0.001}$ at 632.8 nm, and waveguide losses of 1.2 dB/cm have been demonstrated. In addition, we have qualified the film properties between each growth step and between the substrate to layer interface, directly from the measured optical data.

The waveguide properties are reported for wide bandgap gallium nitride (GaN) structures grown by metal organic vapor phase epitaxy on sapphire using a AlN/GaN short period-superlattice (SPS) buffer layer system. A detailed optical characterization of GaN structures has been performed using the prism coupling technique in order to evaluate its properties and, in particular, the refractive index dispersion and the propagation loss. In order to identify the structural defects in the samples, we performed transmission electron microscopy analysis. The results suggest that AlN/GaN SPS plays a role in acting as a barrier to the propagation of threading dislocations in the active GaN epilayer; above this defective region, the dislocations density is remarkably reduced. The waveguide losses were reduced to a value around 0.65dB/cm at 1.55 μm, corresponding to the best value reported so far for a GaN-based waveguide.