In-plane Motion Measurement Research Articles

Detection of In-Plane Movement in Electrically Actuated Microelectromechanical Systems Using a Scanning Electron Microscope.

The measurement of in-plane motion in microelectromechanical systems (MEMS) is a challenge for existing measurement techniques due to the small size of the moving devices and the low amplitude of motion. This paper studied the possibility of using images obtained using a scanning electron microscope (SEM) together with existing motion detection algorithms to characterize the motion of MEMS. SEM imaging has previously been used to detect motion in MEMS device. However, the differences in how SEM imaging and optical imaging capture motion, together with possible interference caused by electrical actuation, create doubts about how accurately motion could be detected in a SEM. In this work, it is shown that existing motion detection algorithms can be used to detect movement with an amplitude of 69 nm. In addition, the properties of SEM images, such as bright edges, complement these algorithms. Electrical actuation was found to cause error in the measurement, however, the error was limited to regions that were electrically connected to the actuating probes and minimal error could be detected in regions that were electrically insulated from the probes. These results show that an SEM is a powerful tool for characterizing low amplitude motion and electrical contacts in MEMS and allow for the detection of motion under 100 nm in amplitude.

A two-axis in-plane motion measurement system based on optical beam deflection

Measurement of in-plane motion with high resolution and large bandwidth enables model-identification and real-time control of motion-stages. This paper presents an optical beam deflection based system for measurement of in-plane motion of both macro- and micro-scale motion stages. A curved reflector is integrated with the motion stage to achieve sensitivity to in-plane translational motion along two axes. Under optimal settings, the measurement system is shown to theoretically achieve sub-angstrom measurement resolution over a bandwidth in excess of 1 kHz and negligible cross-sensitivity to linear motion. Subsequently, the proposed technique is experimentally demonstrated by measuring the in-plane motion of a piezo flexure stage and a scanning probe microcantilever. For the former case, reflective spherical balls of different radii are employed to measure the in-plane motion and the measured sensitivities are shown to agree with theoretical values, on average, to within 8.3%. For the latter case, a prototype polydimethylsiloxane micro-reflector is integrated with the microcantilever. The measured in-plane motion of the microcantilever probe is used to identify nonlinearities and the transient dynamics of the piezo-stage upon which the probe is mounted. These are subsequently compensated by means of feedback control.

In-plane vibration characterization of microelectromechanical systems using acousto-optic modulated partially incoherent stroboscopic imaging

A technique using acousto-optic modulated partially incoherent stroboscopic imaging for measurement of in-plane motion of microelectromechanical systems (MEMS) is presented. Vibration measurement is allowed by using flashes of the partially incoherent light source to freeze the positions of the microstructure at 12 equally spaced phases of the vibration period. The first-order diffracted beam taken out by an acousto-optic modulator (AOM) from the light beam of a laser is made partially incoherent by a rotating diffuser and then serves as the stroboscopic light source. Both the MEMS excitation signal and the flash control signal are provided by a dual-channel function generator. The main advantage of this measurement method is the absence of a stroboscopic generator and a high speed digital camera. Microscale prototypes are fabricated and tested. Quantitative estimates of the harmonic responses of the prototypes are obtained from the recorded images. The results agree with those obtained with a commercial MEMS motion analyzer TM with relative errors less than 2%.

Micro-motion analyzer used for dynamic MEMS characterization

A computer-controlled micro-motion analyzer (MMA) to study the dynamic behavior of movable structures of MEMS is described in this paper. It employs two optical nondestructive methods—computer microvision for in-plane motion measurement and phase-shifting interferometry for out-of-plane motion measurement. This fully integrated system includes a high-performance imaging system, drive electronics, data acquisition and data analysis software. This system can freeze the fast motions of MEMS devices using strobed illumination and measure motions in three dimensions with nanometer accuracy. The static measurement accuracy and repeatability of the system is calibrated by a step height standard which is certified by National Institute of Standards and Technology (NIST). The capabilities of this system are illustrated with a study of the dynamic behaviors of a surface micromachined polysilicon micro-resonator.

Selective Vibrational Detachment of Microspheres Using Optically Excited In-Plane Motion of Nanomechanical Beams

Optical excitation plays an important role in the actuation of higher flexural and torsional modes of nanoelectromechanical oscillators. We show that optical fields are efficient for excitation, direct control, and measurement of in-plane motion of cantilever-type nanomechanical oscillators. As a model system, 200- and 250-nm-thick single-crystal silicon cantilevers with dissimilar lengths and widths ranging from 6 to 12 microm and 500 nm to 1 microm, respectively, were fabricated using surface micromachining and dynamically analyzed using optical excitation and interferrometric detection. Three-dimensional finite element analysis incorporating shear, rotational inertia, cross-sectional deplanation, and nonideal boundary conditions due to the structural undercut describe the dynamics of the nanomechanical structures adequately. The quality factor of a particular in-plane harmonic was consistently higher than the transverse mode. The increased dissipation of the out-of-plane mode was attributed to material and acoustic loss mechanisms. The in-plane mode was used to demonstrate vibrational detachment of submicrometer polystyrene spheres on the oscillator surface. In contrast, the out-of-plane motion, even in the strong nonlinear impact regime, was insufficient for the removal of bound polystyrene spheres. Our results suggest that optical excitation of in-plane mechanical modes provide a unique mechanism for controlled removal of particles bound on the surface of nanomechanical oscillators.

Novel Fabrication Process for the Integration of MEMS Devices with Thick Amorphous Soft Magnetic Field Concentrators

AbstractThis paper reports a novel fabrication process enabling the integration of mechanical MEMS devices with thick amorphous soft magnetic field concentrators. The integration process combines silicon on insulator technology for the MEMS device fabrication and epoxy-resin-based attachment of 18-µm-thick amorphous soft magnetic ribbons followed by a wet chemical structuring process. The fabrication process is reported on the basis of a field-concentrator-based resonant magnetic sensor combining an electrostatically driven micromechanical resonator and a planar magnetic field concentrator with two narrow gaps. For realization of the concentrator gaps, the integration process is extended by micro-patterning of the soft magnetic ribbons via UV-laser ablation using an excimer laser system. The characterization of the fabricated resonant magnetic sensor using a stroboscopic video microscope for in-plane motion measurement shows a high sensitivity of 390 kHz/T at a magnetic flux density of 158 µT.

A differential laser Doppler system for one-dimensional in-plane motion measurement of MEMS

The differential laser Doppler technique is used to measure one-dimensional in-plane motions in micro-electro-mechanical systems in this paper. This method provides real-time measurement of the velocity and derives the displacement from the integral of velocity. The working principle and optical layout of the system are explained. The vibration of the movable comb of a silicon micromachined resonator is measured by this system and the uncertainty caused by high order modes of vibration is discussed. The repeatability of displacement measurements is 0.9 μm. Compared with computer micro-vision method, there is a discrepancy of 0.5 μm in the results of maximum amplitudes of displacements.

The effect of surface characterization and laser beams polarization on laser Doppler vibrometry

In a laser Doppler vibrometry, the characterization of the measured surface plays an important role in both in-plane and out-of-plane surface motion measurements. Experimental data is presented for the in-plane optical probe configuration, where the vibrating surface is illuminated symmetrically by two laser beams. However, some of the conclusions of the present study apply also to out-of-plane vibration measurements. It is found that certain surfaces perform better than others. How the surface character affects the in-plane surface motion measurement (in particular, the signal-to-noise ratio and the probe alignment) is studied. The surfaces studied are lathe-finished, polished aluminum and steel surfaces and two types of retroreflecting tapes from 3M company. Also, the profiles of the metallic surfaces are obtained with a profilometer. A simple model is used to relate the surface characteristics to the performance of in-plane motion measurement. The effect of polarization of the two laser beams is also studied, including the depolarization of the light by the surface. [Work supported by ONR.]

A Close Look at the Measurement of Shock Data: Lessons Learned

Pyroshock testing and analysis is one of the most difficult regimens in the field of structural dynamics. The harsh and often-unpredictable environment has caused relatively poor behavior of the measurements systems used, often for reasons that were not well-understood. This paper reports on a study that was performed with the goal of better understanding the problem areas and development of methods for improving results. Specific areas addressed include: characterization of the broadband response and evaluation of its effects on standard measurement systems, transducer mounting and cabling techniques, measurement of inplane motion, and the problem of justifying/normalizing the results obtained by different data acquisition systems.