There is a great need for techniques that will permit the evaluation of the micromechanical state of micro-electro-mechanical system (MEMS) devices, at all steps of manufacturing, with respect to material properties, as well as of lifetime and for monitoring mechanical performances of MEMS actuators. We propose a new approach, based on integrated optical read-out using a Mach-Zehnder interferometer (MZI), monolithically integrated on the top of an electrostatically rotatable micromirror loaded with the sensing arm of MZI. The working principle of MZI read-out is based on the local change of the effective refractive index of guided waves of MZI, induced by strains of the deformable structure. A single-mode buried channel waveguide based on the silica/silicon oxinitride/silica structure is used, presenting optical attenuation of 0.6 dB/cm. The coupling of the standard optical fiber to the waveguide is based on the V-groove technique, supplemented by micromechanical sawing of the silicon substrate. For TE polarization, the set of obtained parameters is a coupling efficiency of about 55% with a horizontal misalignment of ±0.5 µm, a vertical misalignment of ±0.7 µm, and angular precision of ±0.2 deg on <110> directions of the silicon substrate.
In this paper we present a new family of MOEMS device, which can be used as high resolution optical resonant pressure sensor. The architecture contains a membrane loaded with an optical branch of a Mach-Zehnder interferometer (MZI), monolithically integrated on top of a Si substrate. The measuring arm of MZI is crossing the MEMS actuator based on a piezoelectric thin-film PZT transducer integrated on SOI membrane. The PZT transducer is excited by applying a sinusoidal voltage from a waveform generator. The working principle of MZI read-out is based on the change of effective refractive index of guided waves of MZI, induced by displacements of the deformable structure via the elastooptic effect and waveguide elongation. When the membrane operating at resonance frequency, the application of a pressure on the membrane produces a significant shift of resonance frequency corresponding to a loaded pressure. For the characterisation of dynamic characteristic study of microdevices, the advanced testing methods are necessary. The point-wise measurement system was combined with the multifunctional interferometric platform based on Twyman-Green microinterferometer, working in stroboscopic mode. The prototype of the pressure sensor was evaluated and measurement results are presented.
There is a great need for techniques that will permit the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer, monolithically integrated into the PZT actuated membrane and electrostatically actuated torsional micromirror. The application of membrane-type structure is in the area of pressure sensors. The monolithically integrated MZI on movable torsional mirror seems to be an easy solution for monitoring mechanical performances during lifetime of micromirror.
While testing electrical properties in microsystems is a well-developed art, the testing of mechanical properties of MEMS devices is not. There is a great need for techniques that will allow the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer (MZI), monolithically integrated with the piezoelectric (PZT) actuated membrane.
A very broad field of relevant technologies and testing methods for silicon micromechanical elements had to be limited to specific elements and adapted methodologies including experimental and numerical methods. In particular, the bimorph micromembranes under buckling are key elements for investigations of their mechanical properties. Due to optical quality of silicon-based layers deposited on micromechanical devices under consideration, the two-beam interferometry with computer interferogram processing is well adapted for shape and deformation measuring, while the nanoindentation is able to extract the hardness as well as the Young’s modulus. In this contribution, we investigate the silicon square membranes prestressed by deposition of silicon oxinitride (SiOxNy) films fabricated by PECVD. The combination of experimental techniques with fine elements method (FEM) proposed here offers a powerful tools for investigation of residual stress of SiOxNy layers. The distribution of residual stress is monitored as a function of the refractive index of SiOxNy films, establishing the correlation between the optical and micromechanical properties of deposited thin films.
While testing electrical properties in microsystems is a well-developed art, the testing of mechanical properties of MEMS devices is not. There is a great need for techniques that will permit the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer (MZI). MZI is monolithically integrated on top of a electrostatically rotatable micromirror loaded with the sensing arm of MZI. A single mode buried channel waveguide based on silica/silicon oxinitride/silica structure is used. It performs a low optical attenuation and a coupling efficiency of 55% from waveguide to a standard fiber, connecting MZI to outside world (light source and detector). The working principle of MZI read out is based on the change of effective refractive index of guided waves of MZI induced by displacement of the deformable structure, obtained via the elastooptic effect. The technology process steps with special emphasis to the fiber-to-waveguide coupling based on V-grooves is detailed here. Our goal is aiming to obtain an angular alignment of ± 0.2 deg. of V-groove walls with <110> directions and the vertical misalignment not, exceeding ± 0.6 μm.
While testing electrical properties in microsystems is a well-developed art, the testing of mechanical properties of MEMS devices is not. There is a great need for techniques that will permit the evaluation of MEMS devices, in all stages of manufacturing, with respect to material and micromechanical properties. In this contribution we propose a new approach, based on the integrated optical read-out using a Mach-Zehnder interferometer, monolithically integrated into the PZT actuated membrane.
In this paper we introduce a conventional interferometry system for MEMS/MOEMS characterization. We investigate the opto-mechanical properties of silicon micromembranes, where a thin film of PECVD SiOxNy was deposited. Monitoring the quality of this deposition we demonstrated the fabrication of technology for optical channel waveguides, compatible with the integration on micromechanical structures: based on low-stress and low-loss SiOxNy thin layers.
In this article we present a new micromachined platform for coupling the optical fibers to waveguides of Mach-Zehnder interferometers, supporting fibers in the same wafer as a waveguide wafer. Using standard CMOS technologies, like a UV photolithography, KOH wet etching of Si(100) wafer, sputtering of metal layers, RIE etching the fabrication of a very precise platform is demonstrated.
In the last decade, the advances in the MEMS technology lead to the integration of optical structures with MEMS. This association between MEMS technologies and integrated optical structures may provide complex functionality such as sensing, modulation or switching. Optical MEMS integrated on silicon are very attractive in terms of potential for cheap mass production and compatibility with CMOS technologies. In this paper we present the technology of SiON waveguide fabrication including aspects of PECVD and micromachining. PECVD process optimisation in order to increase the waveguide performances is presented. Finally the integrated opto-mechanical sensing structures are discussed.
In this paper, we present a method for the internal stress characterization of silicon membranes with silicon oxynitride thin films (SiOxNy) deposited by PECVD (plasma enhanced chemical vacuum deposition). Connecting the interferometric measurements (Twyman-Green interferometer) of out-of-plan displacements of SiOxNy-loaded membranes with evaluation of micromechanical parameters (Young's modulus, Poisson ratio) obtained by nanoindentation we evaluated the residual stress of SiOxNy thin films via point-wise deflection technique. The magnitude of stress is monitored as a function of the refractive index of SiOxNy establishing the relationship between the optical and micromechanical properties of deposited films.
The full-field interferometry is very well suited for evaluation of micromechanical and material properties of microsystems. In this paper, we presented a Twyman-Green interferometer for MEMS/MOEMS testing. The measurements of out-of-plan displacements of special silicon membranes with thin film of SiOxNy deposited by PECVD enable the analysis of opto=mechanical properties.
In view of applications of SiOxNythin films in MOEMS technology, a study of optomechanical characteristics of this material PECVD deposited are investigated. To optimize the quality of SiOxNy layers we established the relationship between the chemical properties, optical performances and micromechanical stress of deposited films. To use the SiOxNy thin film for the core layer of a channel waveguide, we need to obtain a structure with low optical attenuation, well-controlled refractive index, and low-internal stress. To study the stress characteristics of SiOxNy material we used an interferometric technique, and we fabricated for this purpose special membranes with deposition of variable quality SiOxNy thin films.
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