MEMS Systems Research Articles

Stroke saturation on a MEMS deformable mirror for woofer-tweeter adaptive optics

High-contrast imaging of extrasolar planet candidates around a main-sequence star has recently been realized from the ground using current adaptive optics (AO) systems. Advancing such observations will be a task for the Gemini Planet Imager, an upcoming "extreme" AO instrument. High-order "tweeter" and low-order "woofer" deformable mirrors (DMs) will supply a >90%-Strehl correction, a specialized coronagraph will suppress the stellar flux, and any planets can then be imaged in the "dark hole" region. Residual wavefront error scatters light into the DM-controlled dark hole, making planets difficult to image above the noise. It is crucial in this regard that the high-density tweeter, a micro-electrical mechanical systems (MEMS) DM, have sufficient stroke to deform to the shapes required by atmospheric turbulence. Laboratory experiments were conducted to determine the rate and circumstance of saturation, i.e. stroke insufficiency. A 1024-actuator 1.5-microm-stroke MEMS device was empirically tested with software Kolmogorov-turbulence screens of r(0) =10-15 cm. The MEMS when solitary suffered saturation approximately 4% of the time. Simulating a woofer DM with approximately 5-10 actuators across a 5-m primary mitigated MEMS saturation occurrence to a fraction of a percent. While no adjacent actuators were saturated at opposing positions, mid-to-high-spatial-frequency stroke did saturate more frequently than expected, implying that correlations through the influence functions are important. Analytical models underpredict the stroke requirements, so empirical studies are important.

3-D Field Path Adjustments of an In-Mold Electromagnetic Stirrer for Steel Mill Application

The existing in-mold electromagnetic stirrers (M-EMS) that are widely applied in the steel industries have experienced low efficiencies due to the high operational temperatures and open system structures. Based on simple mechanical attachments and verified by detailed 3-D electromagnetic field analyses, this paper will propose a guided field path arrangement that can enhance the overall performance of an M-EMS system by a factor of 28% in the designated stirring directions while maintaining the same energy inputs. Such evident improvements will certainly provide a valuable design and adjustment guidance for the related metal industries.

Application of Modified Arnoldi Algorithm to Passive Macromodeling of MEMS

The demand for accurately simulating dynamical responses of complex MEMS and NEMS systems leads to intensive studies in reduced-order modeling methods. We apply a modified Block Arnoldi algorithm to significantly reduce the run time and usage of computer resource for such calculations, while preserving essential properties. The 2n x 2n matrix in the computation is replaced by a n x n matrix and the FLOP count is reduced from (56n(3) - 216n(2) + 22n) / 3 to (7n(3) - 54n(2) + 11n) / 3. The CPU run time for a resonator example of n = 39 is reduced from 0.091 second to 0.080 second. For a butterfly gyroscope example with a larger matrix size, n = 17361, the CPU time is reduced from 4343 seconds to 1528 seconds, achieving 65% improvement.

Metal organic frameworks for chemical recognition

The need for real-time, compact, and inexpensive chemical detectors has become more pressing in recent years. Homeland security and defense applications need effective portal monitoring, chemical weapons sensing, and water quality testing. Devices that can serve as personal exposure monitors, provide advance warning of food spoilage, and enable breath analyzers to uncover pre-symptomatic infection are also in demand. These applications pose many challenges because they require high levels of sensitivity and specificity in small, economical packages. Many existing technologies, such as mass spectrometry and chemiluminescence, lack the combination of sensitivity, selectivity, portability, and low cost needed for these applications. Micro electrical-mechanical systems (MEMS) offer a potential solution that can be cheaply mass produced. Microcantilever sensors have many of the desired characteristics and can be exquisitely sensitive platforms for chemical and biosensing.1 These devices require simple instrumentation, and arrays of cantilevers on a single chip can provide sensitivity to multiple analytes. Yet, such systems still need better recognition chemistries that can identify a broad range of analytes. The tailorable nanoporosity and ultrahigh surface area of metal organic frameworks (MOFs) make them ideal candidates for recognizing analytes in sensing applications. A typical MOF consists of metal cations, such as Zn(II), linked by anionic organic linker groups, such as carboxylates, yielding a rigid but open framework that accommodates guest molecules. An intriguing aspect of these frameworks is their adsorbateinduced structural flexibility.2 The unit cell dimensions of some MOFs can vary by as much as 10% when molecules are absorbed within their pores.3 This behavior suggests a signal transduction mechanism, in which an adsorbate induces Figure 1. The structure of theMOFHKUST-1 (green: copper; red: oxygen; black: carbon; white: hydrogen) enables stress-induced chemical detection when a thin layer is integrated on a microcantilever surface. In this view, the exchangeable axial coordination sites on the Cu(II) ions are unoccupied.

Welding of Metallic Foil with Electron Beam

In this study, microelectron beam welding was applied to the joining of two thin metal foils. An electron beam is adaptable to microwelding due to its deep penetration and thin width. The foil materials used were SUS and Ti with a thickness of 20 µm. The relationship between the input energy of electron beam irradiation and the size of the heat affected zone was investigated. Furthermore, spot welding and overlap welding were carried out for foils of either the same or dissimilar materials. The surface and cross section of the welded zone were observed by a scanning electron microscope (SEM) or confocal laser scanning microscope (CLSM). In the case of the same material, it was possible to weld two overlapped Ti foils (marked as Ti/Ti) with thickness of 20 µm. In the case of dissimilar materials, it was possible to weld SUS304 was top and Ti was bottom (marked as SUS304/Ti) with thickness of 20 µm. The results show that microwelding can be considered a new technology for microelectrical mechanical systems (MEMS) in addition to microfabrication.

21109 MEMS機械構造の電気回路化(基調講演,MEMS技術,OS.3 機械工学が支援する微細加工技術(半導体,MEMS,NEMS))

MEMS or micro electromechancal systems have been started from the field of microfabrication processes based upon the semiconductor fabrication technologies. Significance of MEMS is in the implementation capability of micromechanical components with integrated electrical circuits. MEMS actuators on the first emerging stage were simply micromechancial structures that could be electrically controlled. MEMS devices today, on the other hand, are embedded in electrical circuit and they behaves like a part of electronics. In this talk we present a few such examples of MEMS actuators integratd with control electronics. We also show a home made multiphysics MEMS simulator based on Qucs (quite universal circuit simulator), a general public licensed electrical circuit simulator. The newly develop simulator can handle DC and AC behavior calculation of electrostatic atuators in both small and large amplitude domains including typical electrostatic hysterisys analysis.

A KICKED OSCILLATOR AS A MODEL OF A PULSED MEMS SYSTEM

In this paper, we study the behavior of a MEMS oscillator by applying methods of nonlinear dynamics. We model the system as a kicked damped oscillator and obtain the iterative maps that describe the MEMS system. The dynamics of the maps are studied numerically: we present a study of limit cycles and their rotation numbers and show how the control parameters and initial conditions may affect the output frequencies.

Real-time on-line blend uniformity monitoring using near-infrared reflectance spectrometry: A noninvasive off-line calibration approach

A robust, noninvasive, real-time, on-line near-infrared (NIR) quantitative method is described for blend uniformity monitoring of a pharmaceutical solid dosage form containing 29.4% (w/w) drug load with three major excipients (crospovidone, lactose, and microcrystalline cellulose). A set of 21 off-line, static calibration samples were used to develop a multivariate partial least-squares (PLS) calibration model for on-line prediction of the API content during the blending process. The concentrations of the API and the three major excipients were varied randomly to minimize correlations between the components. A micro electrical-mechanical system (MEMS) based portable, battery operated NIR spectrometer was used for this study. To minimize spectral differences between the static and dynamic measurement modes, the acquired NIR spectra were preprocessed using standard normal variate (SNV) followed by second derivative Savitzky-Golay using 21 points. The performance of the off-line PLS calibration model were evaluated in real-time on 16 laboratory scale (30 L bin size) blend experiments conducted over 3 months. To challenge the robustness of the off-line calibration model, several blend experiments were conducted using a different bin size, faster revolution speed and variations in the potency of the API. Employing the PLS calibration model developed using the off-line calibration approach, the real-time API NIR (%) predictions for all experiments were all within 90–110%. These results were confirmed using the conventional thief sampling of the final blend followed by high performance liquid chromatography (HPLC) analysis. Further confirmation was established through content uniformity by HPLC of manufactured tablets. Finally, the optimized off-line PLS method was successfully transferred to a production site which involved using a secondary NIR instrument with a 15-fold scale-up in bin size from development.

Study of a MEMS-based Shack-Hartmann wavefront sensor with adjustable pupil sampling for astronomical adaptive optics

We introduce a Shack-Hartmann wavefront sensor for adaptive optics that enables dynamic control of the spatial sampling of an incoming wavefront using a segmented mirror microelectrical mechanical systems (MEMS) device. Unlike a conventional lenslet array, subapertures are defined by either segments or groups of segments of a mirror array, with the ability to change spatial pupil sampling arbitrarily by redefining the segment grouping. Control over the spatial sampling of the wavefront allows for the minimization of wavefront reconstruction error for different intensities of guide source and different atmospheric conditions, which in turn maximizes an adaptive optics system's delivered Strehl ratio. Requirements for the MEMS devices needed in this Shack-Hartmann wavefront sensor are also presented.

Measurement of Young’s modulus and Poisson’s ratio for thin Au films using a visual image tracing system

Abstract The mechanical behavior of small-sized materials has been investigated for many industrial applications, including micro electrical mechanical systems (MEMS) and semiconductors. It is challenging to obtain accurate mechanical property measurements for thin films due to several technical difficulties, including measurement of strain, specimen alignment, and fabrication. We propose use of a visual image tracing (VIT) strain measurement system coupled with a micro-tensile testing unit, which consists of a piezoelectric actuator, a load cell, a microscope, and two CCD cameras. Freestanding Au films, 500 μm wide and 1, 2, and 5 μm thick prepared by sputtering, were tested using a VIT system. This system provides real-time strain monitoring up to a resolution of 50 nm during the test, and can be used to simultaneously measure Young’s modulus and Poisson’s ratio of a material. We used this system to obtain the stress–strain curve, Young’s modulus, and Poisson’s ratio of thin Au films.

Ultra-Low-Powered Aqueous Shear Stress Sensors Based on Bulk EG-CNTs Integrated in Microfluidic Systems

Novel aqueous shear stress sensors based on bulk carbon nanotubes (CNTs) were developed by utilizing microelectrical mechanical system (MEMS) compatible fabrication technology. The sensors were fabricated on glass substrates by batch assembling electronics-grade CNTs (EG-CNTs) as sensing elements between microelectrode pairs using dielectrophoretic technique. Then, the CNT sensors were permanently integrated in glass-polydimethylsiloxane (PDMS) microfluidic channels by using standard glass-PDMS bonding process. Upon exposure to deionized (DI) water flow in the microchannel, the characteristics of the CNT sensors were investigated at room temperature under constant current (CC) mode. The specific electrical responses of the CNT sensors at different currents have been measured. It was found that the electrical resistance of the CNT sensors increased noticeably in response to the introduction of fluid shear stress when low activation current (Lt1 mA) was used, and unexpectedly decreased when the current exceeded 5 mA. We have shown that the sensor could be activated using input currents as low as 100 muA to measure the flow shear stress. The experimental results showed that the output resistance change could be plotted as a linear function of the shear stress to the one-third power. This result proved that the EG-CNT sensors can be operated as conventional thermal flow sensors but only require ultra-low activation power ( ~ 1 muW), which is ~ 1000 times lower than the conventional MEMS thermal flow sensors.

Optical temperature sensor and thermal expansion measurement using a femtosecond micromachined grating in 6H-SiC

An optical temperature sensor was created using a femtosecond micromachined diffraction grating inside transparent bulk 6H-SiC, and to the best of our knowledge, this is a novel technique of measuring temperature. Other methods of measuring temperature using fiber Bragg gratings have been devised by other groups such as Zhang and Kahrizi [in MEMS, NANO, and Smart Systems (IEEE, 2005)]. This temperature sensor was, to the best of our knowledge, also used for a novel method of measuring the linear and nonlinear coefficients of the thermal expansion of transparent and nontransparent materials by means of the grating first-order diffracted beam. Furthermore the coefficient of thermal expansion of 6H-SiC was measured using this new technique. A He-Ne laser beam was used with the SiC grating to produce a first-order diffracted beam where the change in deflection height was measured as a function of temperature. The grating was micromachined with a 20 microm spacing and has dimensions of approximately 500 microm x 500 microm (l x w) and is roughly 0.5 microm deep into the 6H-SiC bulk. A minimum temperature of 26.7 degrees C and a maximum temperature of 399 degrees C were measured, which gives a DeltaT of 372.3 degrees C. The sensitivity of the technique is DeltaT=5 degrees C. A maximum deflection angle of 1.81 degrees was measured in the first-order diffracted beam. The trend of the deflection with increasing temperature is a nonlinear polynomial of the second-order. This optical SiC thermal sensor has many high-temperature electronic applications such as aircraft turbine and gas tank monitoring for commercial and military applications.

Determination of the Relative Permittivity, ϵ′, of Methylbenzene at Temperatures between (290 and 406) K and Pressures below 20 MPa with a Radio Frequency Re-Entrant Cavity and Evaluation of a MEMS Capacitor for the Measurement of ϵ′

The relative electric permittivity of liquid methylbenzene has been determined with an uncertainty of 0.01 % from measurements of the resonance frequency of the lowest order inductive-capacitance mode of a re-entrant cavity (J. Chem. Thermodyn. 2005, 37, 684–691) at temperatures between (290 and 406) K and pressures below 20 MPa and at T = 297 K with a MicroElectricalMechanical System (MEMS) interdigitated comb capacitor. For the re-entrant cavity, the working equations were a combination of the expressions reported by Hamelin et al. (Rev. Sci. Instrum. 1998, 69, 255−260) and a function to account for dilation of the resonator vessel walls with pressure that was determined by calibration with methane (J. Chem. Eng. Data 2007, 52, 1660–1671). The results were represented by an empirical equation reported by Owen and Brinkley (Liq. Phys. Rev. 1943, 64, 32–36) analogous to the Tait equation (Br. J. Appl. Phys. 1967, 18, 965–977) with a standard (k = 1) uncertainty of 0.33 %. The values reported by Mospik (J....

Laboratory demonstration of accurate and efficient nanometer-level wavefront control for extreme adaptive optics

A 32 x 32 microelectricalmechanical systems mirror is controlled in a closed-loop adaptive optics test bed with a spatially filtered wavefront sensor (WFS), Fourier transform wavefront reconstruction, and calibration of references with a high-precision interferometer. When correcting the inherent aberration of the mirror, 0.7 nm rms phase error in the controllable band is achieved. When correcting an etched phase plate with atmospheric statistics, a dark hole 10(3) deeper than the uncontrollable phase is produced in the phase power spectral density. Compensation of the mirror's influence function is done with a Fourier filter, which results in improved loop convergence. Use of the spatial filter is shown to reduce the gain variability of the WFS in a quadcell configuration.

Activated iridium oxide films fabricated by asymmetric pulses for electrical neural microstimulation and recording

An efficient and reliable electrochemical method for preparation of activated iridium oxide films (AIROFs) microelectrodes by applying an asymmetric pulse train in Na 2HPO 4 solution was reported. The AIROFs microelectrodes exhibited a very high safe charge injection ( Q inj) limit (∼4.1 mC/cm 2), as well as excellent mechanical and electrochemical stability. Electrode impedance at 1 kHz has been significantly reduced by ∼92%. All of these characteristics are greatly desired for electrical neural microstimulation and recording applications. In addition, the activation method can be easily incorporated into other fabrication processes such as micro electrical mechanical system (MEMS).

315 金属MEMS作製に向けたマイクロ溶接の研究(T02-2 マイクロナノメカトロニクス(2),大会テーマセッション,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

In this study, microelectron beam welding was applied to the joining of two thin metal foils. An electron beam is adaptable to microwelding due to its deep penetration and thin width. The foil materials used were SUS and Ti with a thickness of 20 μm. The relationship between the input energy of electron beam irradiation and the size of the welding spot was investigated. Furthermore, spot welding and overlap welding were carried out for foils of either the same or different materials. The surface and cross section of the welded zone were observed by a scanning electron microscope (SEM) or confocal laser scanning microscope (CLSM). In the case of the same material, it was possible to weld two overlapped Ti foils (marked as Ti/Ti) with thickness of 20 μm. In the case of different materials, it was possible to weld SUS304 was top and Ti was bottom (marked as SUS304/Ti) with thickness of 20 μm. The results show that microwelding can be considered a new technology for microelectrical mechanical systems (MEMS) in addition to microfabrication.

Recent Developments in Polymer MEMS

AbstractPolymer materials, including elastomers, plastics and fibers, are being actively used for MEMS sensors and actuators. Polymer materials provide many advantages in terms of cost, mechanical properties, and ease of processing. In addition, polymers are being investigated for displays, memory, and circuitry. However, the incorporation of polymers for structural or functional purposes in MEMS systems raises new issues and challenges. This article provides a comprehensive review of the recent state of the art of polymer based MEMS—including materials, fabrication processes, and representative devices, including microfluidic valves and tactile sensors. Frequently used materials are reviewed, including polydimethylsiloxane (PDMS), parylene, nanocomposite elastomers, and SU‐8 epoxy.

MEMS for Heterogeneous Integration of Devices and Functionality

Future MEMS systems will be composed of larger varieties of devices with very different functionality such as electronics, mechanics, optics and bio-chemstry. Integration technology of heterogeneous devices must be developed. This article first deals with the current development trend of new fabrication technologies; those include self-assembling of parts over a large area, wafer-scale encapsulation by wafer-bonding, nano imprinting, and roll-to-roll printing. In the latter half of the article, the concept towards the heterogeneous integration of devices and functionality into micro/nano systems is described. The key idea is to combine the conventional top-down technologies and the novel bottom-up technologies for building nano systems. A simple example is the carbon nano tube interconnection that is grown in the via-hole of a VLSI chip. In the laboratory level, the position-specific self-assembly of nano parts on a DNA template was demonstrated through hybridization of probe DNA segments attached to the parts. Also, bio molecular motors were incorporated in a micro fluidic system and utilized as a nano actuator for transporting objects in the channel.

Characterization of magnetostrictive TMR pressure sensors by MOKE

Magnetostrictive tunneling magnetoresistive (TMR) pressure sensors have been developed by combining micro electrical–mechanical systems (MEMS) fabrication techniques with magnetic thin film technology. The sensing TMR elements with magnetostrictive Fe 50Co 50 free layers were placed on different positions on a 2-μm-thick Si membrane structure allowing localized strain measurements. Compressive or tensile mechanical strain up to 0.12% can be introduced by applying different air pressure (0.1–4 bar) to the sealed membrane cavity, which in turn leads to a change in the magnetization direction due to the inverse magnetostrictive effect. For the first time, the strain-induced switching of the free layers has been characterized by means of magneto-optical Kerr effect (MOKE) measurements.

A new UV lithography photoresist based on composite of EPON resins 165 and 154 for fabrication of high-aspect-ratio microstructures

We report a new type of negative-tone photoresist in this paper. The resist is based on a composite of EPON resins 154 and 165 (both from Hexion Specialty Chemicals, Inc., Columbus, OH 43215). These two epoxy-based resins were mixed in an optimal ratio and dissolved in gamma-butyrolactone (GBL) solvent. The mixture was then photosensitized by adding a given amount of triaryl sulfonium salt to obtain a new negative-tone photoresist that can be used in for ultra-high-aspect-ratio microstructure fabrication with UV lithography. Preliminary studies have found that microstructures with heights of more than 1000μm and feature sizes down to 10μm (aspect-ratios of more than 100) can be obtained using the new resist film with ultraviolet lithography. The microstructures have excellent sidewall quality. In this paper, both the material properties and lithography properties of this new type of UV resist will be presented. The potential applications of the new resist in microfabrication and MEMS systems are also discussed.