Optical MEMS

This review provides a comprehensive survey of noise research in MEMS. Some background on noise and on MEMS is provided. We review noise production mechanisms, and highlight work on the theory and modeling of noise in MEMS. Then noise measurements in the specific types of MEMS are reviewed. Inertial MEMS (accelerometers and angular rate sensors), pressure and acoustic sensors, optical MEMS, RF MEMS, surface acoustic wave devices, flow sensors, and chemical and biological MEMS, as well as data storage devices and magnetic MEMS, are reviewed. We indicate opportunities for additional experimental and computational research on noise in MEMS.

A novel optical technique is proposed for the characterization of MEMS resonators. The proposed technique is based on measuring the response of the resonator (resonance frequency and quality factor) optically, which eliminates the electrical parasitic effects. The proposed technique was applied to a comb-drive resonator and the obtained results show good agreement with the standard electrical technique with 2-5% deviation in the resonance frequency and 2-10% in the quality factor.

This article focuses on the rheological, mechanical and optical properties of polydimethylsiloxane (PDMS) relevant for microelectromechanical systems (MEMS). In view of the limited amount of published data, we analyzed the two products most commonly used in MEMS, namely RTV 615 from Bayer Silicones and Sylgard 184 from Dow Corning. As far as rheological parameters are concerned, the viscosity and spin curves were measured. With regard to mechanical properties, we focused on the measurement of the inconstant elastic modulus up to 115% strain. For the optical characterization we concentrate on the optical dispersion and the wavelength-dependent damping coefficient.

This review provides a comprehensive survey of noise research in MEMS. Some background on noise and on MEMS is provided. We review noise production mechanisms, and highlight work on the theory and modeling of noise in MEMS. Then noise measurements in the specific types of MEMS are reviewed. Inertial MEMS (accelerometers and angular rate sensors), pressure and acoustic sensors, optical MEMS, RF MEMS, surface acoustic wave devices, flow sensors, and chemical and biological MEMS, as well as data storage devices and magnetic MEMS, are reviewed. We indicate opportunities for additional experimental and computational research on noise in MEMS.

We present a simple technique to produce active Qswitching in various types of fiber amplifiers by active integration of an electrostatic actuated deformable metallic micro-mirror. The optical MEMS (MOEMS) device acts as one of the laser cavity reflectors and, at the same time, as switching/ modulator element. We aim to obtain laser systems emitting short, high-power pulses and having variable repetition rate. The electromechanical behavior of membrane (bridge-type) was simulated by using electrostatic and modal 3D finite element analysis (FEA). The results of the simulations fit well with the experimental mechanical, electrical and thermal measurements of the components. In order to decrease the sensitiveness to fiber-mirror alignment we are developing novel optical devices based on stressedmetal cantilever-type geometry that allow deflections up to 50 µm with increased reflectivity discrimination during actuation.

We discuss key features of MEMS technology which enable new functionalities of microphotonic devices, that can by summarized as “arrayability”, i.e. the ability to make massively parallel optical devices in a small form factor, “reconfigurability,” the ability to change optical properties spatially and temporaly, and “nano positioning,” the ability to position micro-scale devices with nanometer accuracy. We present an overview of cases where a combination of these features has led to commercial successes by creating new optical functionalities, and discuss materials-related challenges and future trends for optical MEMS research and commercialization.

We present a new novel design for a 1× N digital optical space MEMS switch with a large number of output ports. The switch employs a single rotating micromirror. The rotating micromirror consists of a novel electro-static rotary motor, onto which a 3D mirror structure is assembled using a robotic-based microassembly process. The rotating mirror in the switch can digitally rotate with 480 steps per full revolution in 14.4 msec. A 1.04 dB uniform coupling loss across all output ports is achieved.

This paper presents the modeling of an optical diaphragm behavior for human pulse pressure detection. In this study, the comparison between the performance of the polyimide and silicon nitride diaphragm has been presented. The effects of diaphragm radius and diaphragm thickness on static and frequency response are also investigated. The findings show that the polyimide diaphragm is more sensitive than the silicon nitride diaphragm. In addition, deflection of both diaphragms has linear relationship with the applied pressure The diaphragm radius has more effect on the deflection, sensitivity and resonance frequency as compared to the diaphragm thickness. It can be concluded that the polyimide diaphragm achieves the optimum performance in terms of the deflection, sensitivity, and resonance frequency for human pulse pressure detection. Thus, the polyimide diaphragm has been chosen as the best model in designing an optical micro-diaphragm.

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This paper will outline the concept of Time Multiplexed Optical Shutter (TMOS) technology, the operational principle of an innovative Frustrated Total Internal Reflection (FTIR) display system, discussing the range of advantages and advances offered by this technology.

Stress induced by Focused Ion Beam (FIB) milling of cantilevers fabri-cated on silicon-on-insulator (SOI) wafer has been studied. Milling induces stress gradients ranging from -10MPa/μm to -120MPa/μm, depending on the loca-tion of cantilevers from the point of mill-ing. Simulations were done to estimate the stress in the milled cantilevers.

A wide angle microscanning architecture is presented in which the angular deflection is achieved by displacing the principle axis of a curved silicon micromirror of acylindrical shape, with respect to the incident beam optical axis. The micromirror curvature is designed to overcome the possible deformation of the scanned beam spot size during scanning. In the presented architecture, the optical axis of the beam lays inplane with respect to the substrate opening the door for a completely integrated and self-aligned miniaturized scanner. A micro-optical bench scanning device, based on translating a 200 μm focal length micromirror by an electrostatic comb-drive actuator, is implemented on a silicon chip. The microelectromechanical system has a resonance frequency of 329 Hz and a quality factor of 22. A single-mode optical fiber is used as the optical source and inserted into a micromachined groove fabricated and lithographically aligned with the microbench. Optical deflection angles up to 110 degrees are demonstrated.

In this paper, a hierarchical circuit based approach is used for the development of a reduced-order macro-model for a double-gimballed electrostatic torsional micromirror. The nonlinearity and cross-axis coupling of the micromirror subjected to the differential driving scheme are investigated using the proposed macro-model. The simulation results are used to train a feed-forward neural network which carries out a function approximation of the relation between the desired location and the required driving voltages. The trained neural network is then coded into MAST AHDL. System-level simulation of the micromirror together with the neural network is performed in the SABER TM simulator. It is found that using a feed-forward neural network, the linearity of the micromirror is greatly improved, the steady state of the cross-axis coupling is reduced to a negligible level and the transient response of the cross-axis coupling is also suppressed. This implies that introducing a feed-forward neural network would be useful to simplify the design of the feedback control system for the double-gimballed electrostatic torsional micromirror.

The microelectromechanical systems (MEMS) technology has been widely applied to develop the miniaturized external cavity tunable lasers. In this paper, two integrated MEMS tunable lasers using different configurations are presented and discussed. One uses a deep-etched circular mirror as the external converging reflector. It works in multiple longitudinal modes and has mode hopping. The other employs a deep-etched rotary blazed grating as the reflector and filter simultaneously. Single-longitudinal mode operation is achieved and mode hopping can be avoided.

We present a miniaturized Fourier transform spectrometer (FTS) based on optical microelectromechanical system technology. The FTS is a Michelson interferometer with one scanning mirror. A new type of electrostatic comb drive actuator moves the mirror. We have measured a nonlinearity of the driving system of 60.5 mm for a displacement of 38.5 mm. A method is presented to correct the spectrum to get rid of the nonlinearity. The driving reproducibility is 625 nm. The measured resolution of the spectrometer after the phase correction is 6 nm at a wavelength of 633 nm.

This review provides a comprehensive survey of noise research in MEMS. Some background on noise and on MEMS is provided. We review noise production mechanisms, and highlight work on the theory and modeling of noise in MEMS. Then noise measurements in the specific types of MEMS are reviewed. Inertial MEMS (accelerometers and angular rate sensors), pressure and acoustic sensors, optical MEMS, RF MEMS, surface acoustic wave devices, flow sensors, and chemical and biological MEMS, as well as data storage devices and magnetic MEMS, are reviewed. We indicate opportunities for additional experimental and computational research on noise in MEMS.

The integration of microactuators within a silicon photonic chip gave rise to the field of optical micro-electro-mechanical systems (MEMS) that was originally driven by the telecommunication market. Following the latter's bubble collapse in the beginning of the third millennium, new directions of research with considerable momentum appeared focusing on the realization and applications of miniaturized instrumen-tation in biology, chemistry, physics and materials science. At the heart of these applications light interferometry is a key optical phenomenon, in which miniaturized scanning inter-ferometers are the manipulating optical devices. Monolithic free-space optical interferometers realized on a silicon chip take advantage of the recent progress in the microfabrication technology that is enabling accurate control of the etching depth, the aspect ratio, the verticality and the curvature of the etched surfaces. The fabrication technology, the library of micro-optical and mechanical components, the realized archi-tectures and their characterization are described in detail in this review, followed by a discussion of the foreseen challenges.

Xerox Corporation has developed a technology platform for on-chip integration of latching MEMS optical waveguide switches and Planar Light Circuit (PLC) components using a Silicon On Insulator (SOI) based process. To illustrate the current state of this new technology platform, working prototypes of a Reconfigurable Optical Add/Drop Multiplexer (ROADM) and a l-router will be presented along with details of the integrated latching MEMS optical switches. On-chip integration of optical switches and PLCs can greatly reduce the size, manufacturing cost and operating cost of multi-component optical equipment. It is anticipated that low-cost, low-overhead optical network products will accelerate the migration of functions and services from high-cost long-haul markets to price sensitive markets, including networks for metropolitan areas and fiber to the home. Compared to the more common silica-on-silicon PLC technology, the high index of refraction of silicon waveguides created in the SOI device layer enables miniaturization of optical components, thereby increasing yield and decreasing cost projections. The latching SOI MEMS switches feature moving waveguides, and are advantaged across multiple attributes relative to alternative switching technologies, such as thermal optical switches and polymer switches. The SOI process employed was jointly developed under the auspice of the NIST APT program in partnership with Coventor, Corning IntelliSense Corp., and MicroScan Systems to enable fabrication of a broad range of free space and guided wave MicroOptoElectroMechanical Systems (MOEMS).

This paper proposes a novel method for measuring blood plasma and serum viscosity with a microcan-tilever-based MEMS sensor. MEMS cantilevers are made of electroplated nickel and actuated remotely with magnetic field using an electro-coil. Real-time monitoring of cantilever resonant frequency is performed remotely using diffraction gratings fabricated at the tip of the dynamic cantilevers. Only few nanometer cantilever deflection is sufficient due to interferometric sensitivity of the readout. The resonant frequency of the cantilever is tracked with a phase lock loop (PLL) control circuit. The viscosities of liquid samples are obtained through the measurement of the cantilever's frequency change with respect to a reference measurement taken within a liquid of known viscosity. We performed measurements with glycerol solutions at different temperatures and validated the repeatability of the system by comparing with a reference commercial viscometer. Experimental results are compared with the theoretical predictions based on Sader's theory and agreed reasonably well. Afterwards viscosities of different Fetal Bovine Serum and Bovine Serum Albumin mixtures are measured both at 23 °C and 37 °C, body temperature. Finally the viscosities of human blood plasma samples taken from healthy donors are measured. The proposed method is capable of measuring viscosities from 0.86 cP to 3.02 cP, which covers human blood plasma viscosity range, with a resolution better than 0.04 cP. The sample volume requirement is less than 150 ll and can be reduced significantly with optimized cartridge design. Both the actu-ation and sensing are carried out remotely, which allows for disposable sensor cartridges.

Inexpensive optical MEMS gas and chemical sensors offer chip-level solutions to environmental monitoring, industrial health and safety, indoor air quality, and automobile exhaust emissions monitoring. Previously, Ion Optics, Inc. reported on a new design concept exploiting Si-based suspended micro-bridge structures. The devices are fabricated using conventional CMOS compatible processes. The use of photonic bandgap (PBG) crystals enables narrow band IR emission for high chemical selectivity and sensitivity. Spectral tuning was accomplished by controlling symmetry and lattice spacing of the PBG structures. IR spectroscopic studies were used to characterize transmission, absorption and emission spectra in the 2 to 20 micrometers wavelength range. Prototype designs explored suspension architectures and filament geometries. Device characterization studies measured drive and emission power, temperature uniformity, and black body detectivity. Gas detection was achieved using non-dispersive infrared (NDIR) spectroscopic techniques, whereby target gas species were determined from comparison to referenced spectra. A sensor system employing the emitter/detector sensor-chip with gas cell and reflective optics is demonstrated and CO2 gas sensitivity limits are reported.

We demonstrate a MEMS micromirror enabled handheld confocal imaging probe for portable oral cancer detection, where a comparatively large field of view (FOV) was generated through the programmable Lissajous scanning pattern of the MEMS micromirror. Miniaturized handheld MEMS confocal imaging probe was developed, and further compared with the desktop confocal prototype under clinical setting. For the handheld confocal imaging system, optical design simulations using CODE VR® shows the lateral ...

We report on the design, fabrication and applications of different kinds of deformable mirrors based on optical MEMS, which could gain importance in the future for adaptive optics applications. Optical MEMS versatility of fabrication allowed to demonstrate large optical fiber switches, and large arrays of segmented mirrors.

We demonstrated a unique monolithic integration of Fresnel elliptical zone plate (EZP) objective on a 2-axis staggered vertical combdrive micromirror with 500µm by 800µm surface area via direct patterning of reflective binary phase modulation elements on a silicon chip. The need for focusing optics is thus obviated, simplifying the micro-endoscope assembly and improving its form factor. The design of binary phase EZP was guided by simulations based on FFT based Rayleigh-Sommerfeld diffraction model. For dual-axis scanning angles up to 9º by 9º at the image plane, the simulated diffracted Airy disks on a spatial map have been demonstrated to vary from 10.5µm to 28.6µm. Micromirrors scanning ±9º (optical) about both axes are patterned with elliptical zones designed for 7mm focal length and 20þ off-axis 635-nm illumination using 635nm laser. Videos of samples acquired with ~15µm lateral resolution over 1mm × 0.35mm field of view (FOV) at 5.0 frames/second using the device in both transmission and reflectance modes bench-top single-fiber laser scanning confocal microscope confirmed the applicability of the device to microendoscopy.

In this work we present a locally developed MEMS-based technology for the assembly and characterization of optical MEMS components. For the assembly purpose, the processes required for the Si and glass micromachining (oxidation, photolithography and wet etching) are developed in the Laser lab at the faculty of Engineering, Ain Shams University. For the characterization purpose, an automated set-up for the

We demonstrate a MEMS micromirror enabled handheld confocal imaging probe for portable oral cancer detection, where a comparatively large field of view (FOV) was generated through the programmable Lissajous scanning pattern of the MEMS micromirror. Miniaturized handheld MEMS confocal imaging probe was developed, and further compared with the desktop confocal prototype under clinical setting. For the handheld confocal imaging system, optical design simulations using CODE VR® shows the lateral ...

A pplications of microfluidics and MEMS (micro-electromechanical systems) technology are emerging in many areas of biological and life sciences. Non-contact microdispensing systems for accurate, high-throughput deposition of bioactive fluids can be an enabling technology for these applications. In addition to bioactive fluid dispensing, ink-jet based microdispensing allows integration of features (electronic, photonic, sensing, structural, etc.) that are not possible, or very difficult, with traditional photolithographic-based MEMS fabrication methods.

We present a competitive OMEMS (optical micro electromechanical system) readout for displacement. Congruent positioned gratings modulate the light flux caused by a relative in-plane displacement. As demonstrator, an inertial sensor is used consisting of a Si-chip bearing a perforated spring suspended MEMS structure (seismic mass), which is bonded with SU8 to a glass chip featuring vapor deposited Cr-pattern. Both form a partially transparent sandwich structure where the transmittance depends on the position of the movable Si mass. The modulated light flux is generated and detected by an SMD-LED and a phototransistor at the top and bottom side of the sandwich structure, respectively. First results show a high sensitivity of 10 mV/nm displacement of the seismic mass featuring a noise level of about 200 pm/ Hz.

This paper reports on a method for improving the optical efficiency of micromachined reflectors integrated in rubidium vapor cells for application in atomic MEMS sensors. A hybrid bulk micromachining and multilayer PECVD thin film process is used to form the Bragg reflectors on angled sidewalls, which redirect laser light through the vapor cell and back toward the plane of the source with reduced optical power loss. Integrated thin film Bragg reflectors are shown to improve the reflectance of the micromachined surface by almost three times, resulting in an optical return efficiency of two paired dielectric reflectors that is as much as eight times higher then uncoated silicon reflectors. Absorption of the 87 Rb D 1 absorption line at a wavelength of 795 nm in a 1 mm 3 vapor cell is demonstrated experimentally by use of two integrated thin film reflectors with a total optical return efficiency approaching 40%. (M.A. Perez). URL: http://mems.eng.uci.edu (M.A. Perez).

Pedestrian fatalities are around 15% of the traffic fatalities in Europe. A proposed EU regulation requires the automotive industry to develop technologies that will substantially decrease the risk for Vulnerable Road Users when hit by a vehicle. Automatic Brake Assist systems, activated by a suitable sensor, will reduce the speed of the vehicle before the impact, independent of any driver interaction. Long Wavelength Infrared technology is an ideal candidate for such sensors, but requires a significant cost reduction. The target necessary for automotive serial applications are well below the cost of systems available today. Uncooled bolometer arrays are the most mature technology for Long Wave Infrared with low-cost potential. Analyses show that sensor size and production yield along with vacuum packaging and the optical components are the main cost drivers. A project has been started to design a new Long Wave Infrared system with a ten times cost reduction potential, optimized for the pedestrian protection requirement. It will take advantage of the progress in Micro Electro-Mechanical Systems and Long Wave Infrared optics to keep the cost down. Deployable and pre-impact braking systems can become effective alternatives to passive impact protection systems solutions fulfilling the EU pedestrian protection regulation. Low-cost Long Wave Infrared sensors will be an important enabler to make such systems cost competitive, allowing high market penetration.

This paper reports a novel method for simultaneous resonance monitoring of MEMS cantilevers using phase based dynamic measurements without any electrical connections to the sensor array. MEMS cantilevers are made of electroplated nickel and actuated remotely with magnetic field using an electro-coil. To our knowledge this is the first demonstration of simultaneous parallel optical monitoring of dynamic mode micro-cantilever array in liquid environment. Illumination is generated using a laser source and a diffractive pattern generator, which provides 500 W laser power per channel. A compact fiber array based pickup was built for optical readout. Its main advantages are easy customization to different size and pitch of sensor array, and good immunity to electrical noise and magnetic interference as the photo detectors are located away from the electro-coil. The resonant frequency of the cantilever is tracked with a custom multi-channel lock-in amplifier implemented in software. For demonstrating the stability and sensitivity of the system we performed measurements using glycerol solutions with different viscosities. Measured phase sensitivity was 0.9 • /1% of Glycerol/DI-water solution and the standard deviation of measured phase was 0.025 •. The resulting detection limit for Glycerol/DI-water solution was 280 ppm. The proposed method showed robust results with low laser power and very good noise immunity to interference signals and environmental vibrations. The sensor technology demonstrated here is very significant as it is scalable to larger arrays for simultaneous and real-time monitoring of multiple biological and chemical agents during fluid flow.

We demonstrate a MEMS micromirror enabled handheld confocal imaging probe for portable oral cancer detection, where a comparatively large field of view (FOV) was generated through the programmable Lissajous scanning pattern of the MEMS micromirror. Miniaturized handheld MEMS confocal imaging probe was developed, and further compared with the desktop confocal prototype under clinical setting. For the handheld confocal imaging system, optical design simulations using CODE V R R shows the lateral and axial resolution to be 0.98 μm and 4.2 μm, where experimental values were determined to be 3 μm and 5.8 μm, respectively, with a FOV of 280 μm × 300 μm. Fast Lissajous imaging speed up to 2 fps was realized with improved Labview and Java based real-time imaging software. Properties such as 3D imaging through autofocusing and mosaic imaging for extended lateral view (6 mm × 8 mm) were examined for carcinoma real-time pathology. Neoplastic lesion tissues of giant cell fibroma and peripheral ossifying fibroma, the fibroma inside the paraffin box and ex vivo gross tissues were imaged by the bench-top and handheld imaging modalities, and further compared with commercial microscope imaging results. The MEMS scanner-based handheld confocal imaging probe shows great promise as a potential clinical tool for oral cancer diagnosis and treatment.

A wide angle microscanning architecture is presented in which the angular deflection is achieved by displacing the principle axis of a curved silicon micromirror of acylindrical shape, with respect to the incident beam optical axis. The micromirror curvature is designed to overcome the possible deformation of the scanned beam spot size during scanning. In the presented architecture, the optical axis of the beam lays inplane with respect to the substrate opening the door for a completely integrated and self-aligned miniaturized scanner. A micro-optical bench scanning device, based on translating a 200 μm focal length micromirror by an electrostatic comb-drive actuator, is implemented on a silicon chip. The microelectromechanical system has a resonance frequency of 329 Hz and a quality factor of 22. A single-mode optical fiber is used as the optical source and inserted into a micromachined groove fabricated and lithographically aligned with the microbench. Optical deflection angles up to 110 degrees are demonstrated.

After micro-electro mechanical systems (MEMS) devices have been well established, components of higher complexity are now developed. Particularly, the combination with optical components has been very successful and have led to optical MEMS. The technology of choice for us is the silicon-on-insulator (SOI) technology, which has also been successfully used by other groups. The applications presented here give an overview over what is possible with this technology. In particular we demonstrate four completely different devices: a) a 2x2 optical cross connector (OXC) with an insertion loss of about 0.4 dB at a switching time of 500 µs and its extension to a 4x4 OXC, b) a variable optical attenuators (VOA), which has an attenuation range of more than 50 dB, c) a Fourier transform spectrometer (FTS) with a spectral resolution of 6 nm in the visible, and d) an accelerometer with optical readout that achieves a linear dynamic range of 40 dB over ±6g. Except for the FTS, all the applications utilized optical fibers, which are held and selfaligned within the MEMS component by U-grooves and small leaf springs. All devices show high reliability and a very low power consumption.

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After micro-electro mechanical systems (MEMS) devices have been well established, components of higher complexity are now developed. Particularly, the combination with optical components has been very successful and have led to optical MEMS. The technology of choice for us is the silicon-on-insulator (SOI) technology, which has also been successfully used by other groups. The applications presented here give an overview over what is possible with this technology. In particular we demonstrate four completely different devices: a) a 2x2 optical cross connector (OXC) with an insertion loss of about 0.4 dB at a switching time of 500 µs and its extension to a 4x4 OXC, b) a variable optical attenuators (VOA), which has an attenuation range of more than 50 dB, c) a Fourier transform spectrometer (FTS) with a spectral resolution of 6 nm in the visible, and d) an accelerometer with optical readout that achieves a linear dynamic range of 40 dB over ±6g. Except for the FTS, all the applications utilized optical fibers, which are held and selfaligned within the MEMS component by U-grooves and small leaf springs. All devices show high reliability and a very low power consumption.

We have used hot filament chemical vapour deposition HFCVD to fabricate diamond microstructure components for optical micro Ž. electromechanical systems MEMS. In order to demonstrate the wide application range for diamond technology we have made components for different applications such as diffractive optics, laser-to-fibre alignment, and active cooling of high power devices. The free-standing polycrystalline diamond devices were grown on moulds of silicon and fused silica, creating replicas of the moulds. The Ž. structured silicon-on-insulator SOI wafers as replicating moulds for diamond deposition makes it possible to create shapes that can be very useful for laser-to-fibre alignment. The two-step SOI diamond deposition process enables the creation of long and precise capillaries or capillary arrays with a flat top-side here intended for cooling of high power electronic devices. Furthermore, microstructured fused silica has been introduced as mould material, which gives new possibilities in micro-optical mould design since fused silica technology is much more common in optical industry.