MEMS devices are gaining acceptance with many industries, but reliability concerns remain a barrier to entry into many markets. These inherently three-dimensional devices often have considerably more complex production processes and tolerances than standard silicon circuits. In addition, they require characterization not just in a static sense but also during actuation. Previous studies have shown that strobed interferometry is an effective method for complete three dimensional surface characterization of devices moving at frequencies up to 1MHz. To fully characterize MEMS devices, one must also examine the effect of environment on their critical performance parameters. Some devices, such as optical switches, may be subject to high amounts of power during use, and this can deform the devices temporarily or permanently through methods such as crystallization of polysilicon. Also, many devices, particularly for automotive telecommunications, and wireless applications are naturally subjected to a wide variety of environmental conditions. This paper presents measurement results of an optical switch as it is subjected to thermal stresses as an example of environmental characterization using strobed interferometry. A high-power laser is directed onto the device in a configuration equivalent to the desired use condition, and deformation amounts and damage threshold are quantified. Also, the challenges of interferometric dynamic device testing through a cover glass, needed for production characterization, are presented, along with solutions currently in place.

Interferogram analysis techniques able to compute phase or contrast maps from a single interferogram are useful for fast measurements of surface profiles, of out-of-plane displacement fields under thermal or mechanical loading, and of vibration mode shapes. Well known single interferogram techniques are Fast Fourier Transform (FFT) analysis, spatial carrier phase stepping and synchronous detection techniques. These techniques typically need a sample tilting to introduce a fringe spatial carrier and fail when the interferograms contain closed fringes. A 2D fringe pattern demodulation technique which overcomes these limitations is the Vortex Transform method proposed recently by K.G. Larkin et al. In this paper a fully automated version of this technique is described. Then it applied on real interferograms recorded on microdevices by microscopic homodyne interferometry is demonstrated.

We present a methodology for static and dynamic testing of mechanical properties of microelements. The measurement path includes temporal phase shifting interferometry for quantitative static shape elements analysis. This is followed by determination of the resonance frequency by means of modified time average interferometry and transient amplitude and phase maps of vibrating micromembrane capturing and evaluation by phase shifting stroboscopic interferometry. Proper application of combination of these methods allows for quick and accurate analysis of micromembranes and optimization of their manufacturing conditions.

The paper describes methodology, instrumentation, and experiments for the study of the mechanical behavior of MEMS, especially active micromembranes. The technique of speckle interferometry is extended to high microscopic magnification and short wavelength of laser light and two corresponding interferometric solutions are discussed. Challenging issues for the optical measurement are the micrometer lateral size of the details, the nanometer deflection, and the Megahertz frequencies of resonant vibrations. Micromembrane arrays different in size and shape were analysed with respect to piezo response, resonance, and cross-talk. Systematic investigations revealed the complex micromechanical behavior of the microstructures.

White light scanning interference microscopy, with its high axial resolution, is particularly useful for the rapid 3D characterization of MOEMS micro-systems. Although this technique can be used for submicron critical dimension measurement on micron high microelectronic structures, recent tests using a standard system have revealed errors of up to 3 μm in the measurement of lateral position of deep square steps. Thus the 2 μm wide, 75 μm deep teeth of an electrostatic comb structure in a FT MOEMS spectrometer were measured to be nearly 7 μm wide using a Mirau interference objective with the aperture diaphragm of the illumination system fully open in white light. Tests under different conditions show that the error is greatest for the Mirau objective, with the aperture diaphragm fully open at longer wavelengths. In addition, the location of the centre of such structures can vary by up to 1 μm depending on the degree of reference mirror tilt. Investigations of the XZ images of square steps have revealed the presence of "ghost" fringes resulting from diffraction and the conical illumination used. The errors in edge position can be reduced using a Linnik type objective with the aperture diaphragm closed down using shorter wavelength light.

The metrology of refractive microlens arrays is analyzed using Twyman-Green, Mach-Zehnder, and white light interferometers. The advantages and limitations of each are discussed in their application to the measurement of spherical and aspherical microlens arrays.

Tomographic microinterferometry allows for a fast determination of the 3D refractive index distribution in optical elements. In this paper the limitations of this method due to diffraction effects at the edges of microelements or the steps in refractive index distribution inside objects with dimensions comparable to the wavelength are experimentally analyzed and by FDTD based simulations of reconstruction process. The other limitation considered refers to the deviation from a straight light propagation condition assumed in tomographic reconstruction. This problem is analyzed on the base of an experimental analysis of a 3D refractive index distribution in gradient index fiber optics and grin lens. The further modifications of tomographic microinterferometry in order to decrease these limitations are discussed.

A novel broad-band telecom laser source is used to realize a lateral-shear scanning-wavelength interferometer for measuring the thickness of thin plates. We show that the wide tunability range allows to detect samples down to tens of microns with a relative uncertainty of less than 0.5% and a resolution of about 1 nm. A comparable accuracy in the thickness characterization of double-layer structures is also demonstrated. In turn, the wide tunability range needs the dispersion law of the materials to be taken into account in the model for correct thickness evaluation.

MOEMS packing architecture has been a major driving force for miniaturization of fiber optical components and optical communication devices. By using of bulk micromachining technology, V-grooves and micro-pits can be fabricated on a silicon wafer for coupling micro laser diode to fiber or fiber to fiber, and finally integrating into the small modules on chip packages. Because many factors, such as photolithography, material property, wet chemical etching process and operator's skills will influence the geometric accuracy, a precision measurement instrument is needed for in-situ inspection of V-grooves suitable for the critical passive optical alignments. This paper reported a novel 3D confocal profile measurement system for in-situ inspection of the depth of multi-channel V-grooves.

Makyoh topography is an optical surface defect and flatness characterization tool. Its operation principle is based on the whole-field reflection of a collimated beam and defocused detection. This paper reviews the history, the basic principles and applications of the method. The problem of quantitativity is discussed in detail and the solutions are described. The accuracy limits are discussed. Application examples are shown from semiconductor wafer processing and MEMS technology. Comparison is made to related optical and other topographic techniques.

Currently the use of white light interference microscopy for measuring static 3D surface shape typically involves the "snapshot" approach, comprising the pressing of a button and waiting for the 3D "photo". For a standard image acquisition rate of 25 to 60 i/s, the time to result can vary from a few seconds to a few minutes, depending on the depth. Deeper and larger area structures such as those of MOEMS micro-systems can take many minutes. In this work we develop the concept of real time 3D measurement (4D) of non-periodic movement by means of high speed image acquisition and processing. A dedicated high speed CCD camera and FPGA (1 million gates) imaging board processes images 512x512 pixels in size (10 bits) at a rate of 250 i/s, and displays 3D images at up to 5 i/s. A second system based on a CMOS camera has also been tested at acquisition rates of 1017 i/s, but in this case with post processing. The move from "snapshot" to "video" leads to several advantages, such as easier system optimization, higher speed measurement and new applications in the areas of the analysis of moving parts, surface chemical reactions and fragile materials.

We have realized a novel optical microscope that uses the coherent superposition of diffused and diffracted beams. A laser emitting at 670nm is illuminating at oblique incidence the sample surface while a sharp metallic tip is partially obstructing the beam. The coherent superposition of diffracted radiation, coming from the tip sample region, and the reference beam, diffused by the whole surface, is collected in the far field during XY scan, obtained moving the sample only. The aperture between the tip, kept fixed at a working distance of the order of 20μm, and the local surface topography realizes a variable diffracting aperture, producing an intensity variations at the detector plane. We show clear images of a test structure with a resolution better than λ/10. A simple model is used and it is shown to be able to explain the obtained results.

Shape and deformation measurement by moiré topography or interferometry are introduced. By using the integrated phase shifting method proposed by the authors, shape measurements of various objects such as a hand with cell phone and a human face are performed in real-time. The integrated phase-shifting method can analyze the phase information of a projected grating on the object or an interferometric fringe pattern. The phase analysis provides the accurate shape of the object. The object is recorded by an NTSC-TV-CCD camera at 30 frames/second. The analyzed shape or flatness distribution is simultaneously displayed as a moving image of computer graphics. The analyzed shape is observed from any direction directed by a computer mouse in real-time.

An experimental study of the performance of a multi-fiber polarimetric sensor in real time structural health monitoring is carried out. The sensor is in the form of a two-fiber assembly composed of a polarization maintaining (PM) lead-in fiber spliced to a high-birefringent (Hi-Bi) fiber. Experiments are conducted on composite structure under static loading conditions. The results are compared with individual fiber performances. The polarization behavior of the assembly is analyzed theoretically using Stokes matrix method for the monochromatic case.

The frequency of the holographic fringe signal is proportional to the measured object deformation or displacement. Fast Fourier transform (FFT) is the most commoly used signal processing technique for analyzing output fringes. One problem with this approach is that a long data acquisition is required to achieve adequate deformation resolution, typically 5 to 10 fringes are needed. We propose using an autoregressive (AR) model to obtain with the same advantages deformation of an opaque object using holographic interferometry. This deformation will be estimated directly from the model parameters. The theoretical and experimental results obtained indicate that the proposed method has a good accuracy by using a small number of fringes.

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.

We present an improved interferometric system based on surface plasmon resonance (SPR) and phase detection. The system incorporates a SPR device and a total internal reflection (TIR) device used not only to enhance the relative phase-shift between the TE and TM waves but also to keep the output beam to be anti-parallel to the input beam. A pair of quarter-wave-plates (QWPs) is placed in front of and behind, respectively, to the system. This gives rise to optimize the response curve and then the sensitivity. Theoretical simulations have been developed and verified by experimental results. By using this new design, we can always get the best sensitivity regardless weather the systems are manufactured in perfect conditions or not.

Nanoluminescence spectroscopy and imaging techniques are becoming popular to investigate optical properties of semiconductor nanomaterials. Conventional micro-photoluminescence (PL) techniques are affected by diffraction phenomenon, which limits the lateral resolution to approximately 0.6 μm and thus, they cannot provide information of luminescence features with dimension below the classical diffraction limit. This limitation can be overcome by near-field scanning optical microscopy (NSOM) where it is possible to achieve spatial resolution of the order of 50 - 100 nm. InGaN based material has attracted great interest since it plays a key role in the group III-Nitride optoelectronic devices, such as high-brightness blue/green light emitting diodes and laser diodes. In order to retrieve information on the spatial inhomogeneities of the emission patterns in InGaN based materials, we have carried out NSOM-PL measurements on InGaN/GaN multi-quantum wells (MQWs) and InGaN quantum dots (QDs) grown by metal organic chemical vapor deposition (MOCVD). The near-field PL intensity from these samples is found to be spatially inhomogeneous on a sub-micron scale. In the NSOM-PL intensity images, bright island-like features are observed. After deconvolution with the spatial resolution of the NSOM, the size of these features is estimated to be in the range of 100 to 200 nm. The spatially resolved improved optical emission from these InGaN/GaN quantum structures is associated with strain-induced clusters formed at the interface of the multi-layers.

We have developed a local optical probe that uses a sub-wavelength rare-earth-doped glass-ceramic particle as a nanodetector of electromagnetic fields. These particles have the advantage of operating at room temperature with a very good photostability. Fluorescence emission occurs at several wavelengths and we detect the intense one located around 550 nm. The fluorescence responds non-linearly to the excitation. This induces a better sensitivity to strong optical fields, so to localized evanescent fields. We will first describe the probe fabrication procedure. This step is performed with a nanomanipulator which allows the deposition of an adhesive polymer at the extremity of an atomic force microscope tip and then the sticking of the particle at the end of the tip. A reduction of the particle size with a Focused Ion Beam (FIB) is also accomplished. We will then describe some experiments performed on various test samples which demonstrate a subwavelength optical resolution. In particular, the distribution of the electromagnetic field located around nano-holes (diameter 250 nm) in metal films has been imaged.

In mass metrology, the stability of weights, such as standard kilograms, has always been a major concern. Models have been used to describe the various factors that affect mass stability. Surface quality is one important factor that can include the amount and type of pollution present on the surface. However, another important factor is surface roughness. Methods for determining surface roughness differ in their lateral and height resolution and also by the type of information that each method provides, such as: profile, image of defects, power-spectral-density, surface auto-correlation function, or different statistical parameters such as the root-mean-square (rms) height (or roughness) δ.

We propose and demonstrate an original concept of a near-field sensor using the optical feedback properties of a vertical cavity surface-emitting laser as an active principle of detection. This is based on the monitoring perturbations induced in the laser cavity by the backscattered light coming from the specimen. Test images confirm the efficiency of proposed SNOM microscope and a solution for the integration of proposed architecture is given.

In the present work we employ an heuristic method based on evolutionary algorithms for the solution of an inverse problem in near-field optics. The input for the inversion procedure are some of the experimental data that appear in reference 1. In addition, we make use of the direct model proposed in that reference for the iterative solution of the direct problem. This requirement is directly related to the nature of the evolutionary approach employed. We show the possibility to recover, with a high degree of confidence, some parameters of the sample that originated the experimental information. The usefulness of the inverse method is therefore obvious if the recorded data have to be used for metrologic purpose.

In this paper, semiconductor laser feedback interferometry is applied to the characterization of vibrating mass microsensors, such as gyroscopes and accelerometers. Complete characterization of such devices with this technique includes the identification of the vibration modes and the measurement of the resonance curves of the different axes, the determination of resonance frequency, quality factor and the actuation efficiency as functions of different parameters such as pressure. In the case of a gyroscope, tuning of the driving and of the sensing axes can be also performed, as well as the measurement of the Coriolis force. Thanks to its very simple optical implementation, feedback interferometry provides a viable alternative to the standard electrical measurements, and is especially useful for the characterization of prototypes, for which a dedicated electronics circuit is not yet available.

Numerical simulations of the influence the phase step miscalibration and average intensity differentiation between the frames on the calculated interferogram contrast using the temporal phase shifting method (TPS) are presented. The fringe function includes in its argument the amplitude of vibration studied by the time-average method. Some features of the TPS method known from the interferogram phase calculations are confirmed and properties characteristic to contrast determination are established. Experimental studies of vibration resonant mode patterns of silicone microelements provide corroboration of theoretical and numerical findings.

Porous alumina thin membranes containing parallel regular pores of uniform size (nano scale) and normal to substrate surface have been prepared and fabricated. Their fine pore structure has recently made the porous films to be one of the ideal templates for synthesis of nano-structured materials and MEMS (micro-electro-mechanical systems) and separator for separation those small grains from mixed liquid. Unfortunately, the significant macro-mechanical properties of porous alumina thin membrane have not yet been understood clearly. Because the geometry of this kind membrane is multi-scale covered with mm to μm to nm, macro-mechanical behaviors of the porous alumina thin membranes belong to nonlinear mechanics. To measure and calculate those mechanical properties are difficult. Using "temporal speckle pattern interferometry" to measure successfully the large deflection vs perpendicular uniform pressure. Then the mechanical properties of the porous alumina membranes, such as elastic modulus and fracture strength, can be obtained based on plate/shell models and flexile thin membrane model. The results indicate unusual mechanical behavior of it and help us to understand the relations between microstructure and macro mechanical properties.

Digital Holographic Microscope has been employed to obtain an accurate characterization of a micro-hotplate for gas sensing applications. The fabrication of these sensors needs different materials, with different properties and different technological processes, which involve high temperature treatments. Consequently, the structure is affected by the presence of residual stresses, appearing in form of undesired bowing of the membrane. Moreover, when the temperature of the sensor increases, a further warpage of the structure is observed. DHM allows to evaluate, with high accuracy, deformations due to the residual stress and how these deformations are affected by thermal loads. In particular, profiles of the structure have been evaluated both in quasi-static condition and the profile variation due to the biasing of the heater resistor has been measured.

Thin films are the elementary structures in many MEMS devices. Their applications can be found vastly in micromachined silicon pressure sensors. With respect to the specific demands in thin film analysis for microstructures, we present a hybrid approach integrating digital microscopic holographic measurement with finite element analysis in this paper for high-resolution full-field characterization of the micromachined silicon thin film. The pressure-induced membrane deflections are accurately measured with the developed system, and serve as reliable reference data to verify the FE model, which is then applied for strain and stress calculation and sensitivity characterization.

An optical workstation consisting of a surface profiler, laser vibrometer and a high power pulsed laser has been constructed for mechanical testing of MEMS. Through a series of static and dynamic measurements, the performance of a device is determined in seconds. For these measurements the device is induced to move by either using mechanical, electrostatic or optical actuation methods. In the latter case this is achieved by directing high power light pulses onto a silicon surface. The same laser can also be used to trim and frequency tune resonant devices. The workstation has been designed to incorporate single devices, wafers and packaged devices so that devices may be characterised at any stage of processing. The speed and non-contact nature of this workstation makes it suitable for industrial metrology. A variety of MEMS have been characterised, examples of which are presented. The workstation has also proved to be an invaluable tool for determining the cause of device failure in prototype designs.

Polarimetry is effective technique for polarized light fields characterization. It was shown recently that most full “finger-print” of light fields with arbitrary complexity is network of polarization singularities: C points with circular polarization and L lines with variable azimuth. The new singular Stokes-polarimetry was elaborated for such measurements. It allows define azimuth, eccentricity and handedness of elliptical vibrations in each pixel of receiving CCD camera in the range of mega-pixels. It is based on precise measurement of full set of Stokes parameters by the help of high quality analyzers and quarter-wave plates with λ/500 preciseness and 4’ adjustment. The matrices of obtained data are processed in PC by special programs to find positions of polarization singularities and other needed topological features. The developed SSP technique was proved successfully by measurements of topology of polarized speckle-fields produced by multimode “photonic-crystal” fibers, double side rubbed polymer films, biomedical samples. Each singularity is localized with preciseness up to ± 1 pixel in comparison with 500 pixels dimensions of typical speckle. It was confirmed that network of topological features appeared in polarized light field after its interaction with specimen under inspection is exact individual “passport” for its characterization. Therefore, SSP can be used for smart materials characterization. The presented data show that SSP technique is promising for local analysis of properties and defects of thin films, liquid crystal cells, optical elements, biological samples, etc. It is able discover heterogeneities and defects, which define essentially merits of specimens under inspection and can’t be checked by usual polarimetry methods. The detected extra high sensitivity of polarization singularities position and network to any changes of samples position and deformation opens quite new possibilities for sensing of deformations and displacement of checked elements in the sub-micron range.

Real time structural health monitoring using fiber optic sensors is an interesting field of research in recent years. This paper presents the performance of fiber optic polarimetric sensor (FOPS) using plastic fiber. The experiments were conducted on concrete structures using plastic fiber sensor embedded in two different configurations. The dynamic responses of these sensors are experimentally evaluated under different conditions. Their performances are discussed for dynamic applications and the results are compared with that of glass fiber.

In this paper, we present a versatile vibrometer developed to characterize in-plane responses of MEMS. This system can be used either in microscope configuration for very small displacements (nanometer resolution) or in macro configuration for large range of displacement measurements (field of view up to 10 x 10 mm with sub-pixel accuracy). The system is based both on an homemade stroboscope with incremental phase shifts and a digital CCD camera to record a video sequence of the moving MEMS "frozen" by a strobe LED at four equally spaced phases. The periodic motion of the specimen is accurately estimated by computing the value of the displacements between successive images. We have used an interpolation-correlation based image motion estimation algorithm with subpixel accuracy. Both, experimental setup and stroboscopic module used for MEMS motion measurements are described. The correlation estimation method used to calculate the displacements with subpixel accuracy between consecutive frames is also described. Using the vibrometer we have investigated the mode shapes of a silicium cantilever beam with a large field of view, and a subpixel resolution. The experimental measurements are shown to be in good agreement with analytical predictions.

We are making a comprehensive study of the ablation of elemental materials by femtosecond lasers. Specifically, we are examining the ablation of a wide range of metals, under vacuum and in ambient air, using 850-nm wavelength, 100-fs laser pulses in an intensity range approaching and extending beyond the air ionization threshold. We compare ablation rates and examine in detail the morphology and structural integrity of the ablation region, towards gaining greater knowledge of the interaction science as well as constructing empirical models for fabrication guidelines across the periodic table.

In the work, we present a method for direct measurement of the refraction index of air. We designed two coupled glass cells (one evacuated and the other filled by atmospheric air) inserted to plan-parallel Fabry-Perot resonator (F. P. resonator). Two tunable single-frequency lasers pass laser beams through the evacuated and aired cell simultaneously. Two F.-P. resonators are built up by this way: one of them in evacuated cell and the other in the open air cell. If both lasers are tuned along the resonant modes of F.-P. resonators, an optical frequency difference between two adjacent modes can be identified for each resonator. The evacuated one will have another mode-to-mode difference than the aired resonator. With knowledge of these values we can determine the index of refraction very fast. We verified the method with using Michelson interferometer based technique where a glass cell placed to the measurement arm of the interferometer is evacuated by an oil pump. In this case Michelson interferometer monitors changes of the optical path caused by the process of evacuation. Experimental results achieved by the method will be presented.

We report on the characterization of the field diffracted by Au nanoparticles under optical excitation. The spatial distribution of the scattering diagram of the nanoparticles is materialized in real space through photopolymerization. These experiments find their motivations in optics where metallic nanoparticles are thought to find promising applications in plasmonics, but also in chemistry where nanometer scale polymerization mechanisms is a subject of current interest for both fundamental purposes or lithographic applications. For our experiments, the nanoparticles embedded in a photopolymerizable material are deposited on a glass substrate. The sample is then subjected to a global illumination and the field scattered by the particles enables for a local optical activation of the polymerization reaction. The nanometric sensitivity of the polymerization reaction determines the reaction's transfer function and allows for a spatially controlled characterization of the field scattered by the particles. The shape of the resulting polymeric material, representing the particle's spatial diffraction pattern, is subsequently characterized using Atomic Force Microscopy (AFM). For colloidal, randomly dispersed Au nanoparticles excited with linearly polarized light, the scattering induced topography is related to the dipolar response from the particle. More specifically, different components of the scattered field were identified that we assigned to the evanescent and progressive contributions of the dipole's field. Experiments in progress are aimed to study interacting particles with various shapes and sizes.

Stroboscopic interferometry is the most popular method for investigation of active, vibrating elements. The interferograms obtained in measurement steps may be analysed by temporal phase shifting method or by spatial carrier frequency methods. The first one requires sequential capturing of phase-shifted interferograms which complicates the measurement system and introduces high stability requirements for the setup. The spatial methods need a single interferogram with a proper spatial carrier frequency (SCF), so they are more suitable for dynamic events analysis. The most frequently used spatial method is based on Fourier transform of an interferogram with linear SCF and can be applied to analysis of restricted class of elements represented by quasi-linear fringes. This can be easily expanded by considering elements with circular carrier fringes (CCF). In the paper two approaches to analysis of interferograms with CCF, namely: coordinate transform Fourier transform technique and direct filtering Fourier transform technique are explained. The error analysis of both techniques applied for different classes of interferograms is presented. The methodology of CCF interferogram analysis based on FT methods applied for micromembranes is presented and several exemplary results are given.