Description

A journal covering Microsensing, Microactuation, Micromechanics, Microdynamics, and Microelectromechanical Systems (MEMS). Contains articles on devices with dimensions that typically range from micrometers to millimeters, microfabrication techniques, microphenomena; microbearings, and microsystems; theoretical, computational, modeling and control results; new materials and designs; tribology; microtelemanipulation; and applications to biomedical engineering, optics, fluidics, etc. The Journal is jointly sponsored by EDS, the IEEE Industrial Electronics (IE) and Robotics and Automation (RA) societies and is a publication both of IEEE and The American Society of Mechanical Engineers (ASME).

Publisher details

Institute of Electrical and Electronics Engineers

Publications in this journal

• CMOS-Based High-Density Silicon Microprobe Arrays for Electronic Depth Control in Intracortical Neural Recording

  Authors: K. Seidl, S. Herwik, T. Torfs, H.P. Neves, O. Paul, P. Ruther

  Microelectromechanical Systems, Journal of.

  This paper reports on a novel high-density CMOS-based silicon microprobe array for intracortical recording applications. In contrast to existing systems, CMOS multiplexing units are integratedThis paper reports on a novel high-density CMOS-based silicon microprobe array for intracortical recording applications. In contrast to existing systems, CMOS multiplexing units are integrated directly on the slender, needle-like probe shafts. Single-shaft probes and four-shaft combs have been realized with 188 and 752 electrodes, respectively, with a pitch of 40 μm arranged in two columns along 4-mm-long probe shafts. Rather than performing a mechanical translation of the probe shaft relative to the brain tissue to optimize the distance between electrodes and neurons, the electrode position is adjusted by electronically switching between the different electrodes along the shaft. The paper presents the probe concept, the CMOS circuitry design, the applied post-CMOS fabrication process, and the assembled probe systems.

• Multistage Planar Thermoelectric Microcoolers

  Authors: A.J. Gross, Gi Suk Hwang, Baoling Huang, Hengxi Yang, N. Ghafouri, Hanseup Kim, R.L. Peterson, C. Uher, M. Kaviany, K. Najafi

  Microelectromechanical Systems, Journal of.

  Many types of microsystems and microelectromechanical systems (MEMS) devices exhibit improved performance characteristics when operated below room temperature. However, designers rarely pair suchMany types of microsystems and microelectromechanical systems (MEMS) devices exhibit improved performance characteristics when operated below room temperature. However, designers rarely pair such devices with integrated cooling solutions because they add complexity to the system and often have power consumption which far exceeds that of the microsystem itself. We report the design, fabrication, and testing of both one- and six-stage thermoelectric (TE) microcoolers that target MEMS applications through optimization for low-power operation. Both coolers use thin-film Bi₂Te₃ and Sb₂Te₃ as the n-and p-type TE materials, respectively, and operate in a planar configuration. The six-stage cooler has demonstrated a ΔT = 22.3 °C at a power consumption of 24.8 mW, while the one-stage cooler has demonstrated a ΔT = 17.9 °C at a lower power consumption of 12.4 mW.

• Piezoelectric MEMS Energy Harvester for Low-Frequency Vibrations With Wideband Operation Range and Steadily Increased Output Power

  Authors: Huicong Liu, Cho Jui Tay, Chenggen Quan, T. Kobayashi, Chengkuo Lee

  Microelectromechanical Systems, Journal of.

  A piezoelectric MEMS energy harvester (EH) with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized. The MEMS piezoelectric energy harvestingA piezoelectric MEMS energy harvester (EH) with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized. The MEMS piezoelectric energy harvesting cantilever consists of a silicon beam integrated with piezoelectric thin film (PZT) elements parallel-arranged on top and a silicon proof mass resulting in a low resonant frequency of 36 Hz. The whole chip was assembled onto a metal carrier with a limited spacer such that the operation frequency bandwidth can be widened to 17 Hz at the input acceleration of 1.0 g during frequency up-sweep. Load voltage and power generation for different numbers of PZT elements in series and in parallel connections were compared and discussed based on experimental and simulation results. Moreover, the EH device has a wideband and steadily increased power generation from 19.4 nW to 51.3 nW within the operation frequency bandwidth ranging from 30 Hz to 47 Hz at 1.0 g. Based on theoretical estimation, a potential output power of 0.53 μW could be harvested from low and irregular frequency vibrations by adjusting the PZT pattern and spacer thickness to achieve an optimal design.

• In Situ Tuning of Focused-Ion-Beam Defined Nanomechanical Resonators Using Joule Heating

  Authors: L.V. Homann, T. Booth, A. Lei, D.H. Petersen, Z.J. Davis, P. Boggild

  Microelectromechanical Systems, Journal of.

  Nanomechanical resonators have a huge potential for a variety of applications, including high-resolution mass sensing. In this paper, we demonstrate a novel rapid prototyping method for fabricatingNanomechanical resonators have a huge potential for a variety of applications, including high-resolution mass sensing. In this paper, we demonstrate a novel rapid prototyping method for fabricating nanoelectromechanical systems using focused-ion-beam milling as well as in situ electromechanical characterization using a transmission electron microscope. Nanomechanical resonators were cut out of thin membrane chips, which have been prefabricated using standard cleanroom processing. We have demonstrated the fabrication of double-clamped beams with feature sizes down to 200 nm using a fabrication time of 30 min per device. Afterwards, the dynamic and structural properties of a double-clamped beam were measured after subsequent Joule heating events in order to ascertain the dependence of the internal structure on the Q-factor and resonant frequency of the device. It was observed that a change from amorphous to polycrystalline silicon structure significantly increased the resonant frequency as well as the Q-factor of the nanomechanical resonator. Aside from allowing detailed studies of the correlation between internal structure and nanomechanical behavior on an individual rather than a statistical basis, the combination of a short turnaround time and in situ nonlithographic tuning of the properties provide a flexible approach to the development and prototyping of nanomechanical devices.

• A Fully-Passive Wireless Microsystem for Recording of Neuropotentials using RF Backscattering Methods.

  Authors: Helen N Schwerdt, Wencheng Xu, Sameer Shekhar, Abbas Abbaspour-Tamijani, Bruce C Towe, Félix A Miranda, Junseok Chae

  Journal of microelectromechanical systems : a joint IEEE and ASME publication on microstructures, microactuators, microsensors, and microsystems. 20(5):1119-1130.

  The ability to safely monitor neuropotentials is essential in establishing methods to study the brain. Current research focuses on the wireless telemetry aspect of implantable sensors in order toThe ability to safely monitor neuropotentials is essential in establishing methods to study the brain. Current research focuses on the wireless telemetry aspect of implantable sensors in order to make these devices ubiquitous and safe. Chronic implants necessitate superior reliability and durability of the integrated electronics. The power consumption of implanted electronics must also be limited to within several milliwatts to microwatts to minimize heat trauma in the human body. In order to address these severe requirements, we developed an entirely passive and wireless microsystem for recording neuropotentials. An external interrogator supplies a fundamental microwave carrier to the microsystem. The microsystem comprises varactors that perform nonlinear mixing of neuropotential and fundamental carrier signals. The varactors generate third-order mixing products that are wirelessly backscattered to the external interrogator where the original neuropotential signals are recovered. Performance of the neuro-recording microsystem was demonstrated by wireless recording of emulated and in vivo neuropotentials. The obtained results were wireless recovery of neuropotentials as low as approximately 500 microvolts peak-to-peak (μV(pp)) with a bandwidth of 10 Hz to 3 kHz (for emulated signals) and with 128 epoch signal averaging of repetitive signals (for in vivo signals).

• Diamond-on-Polymer Microelectrode Arrays Fabricated Using a Chemical Release Transfer Process

  Authors: A.E. Hess, D.M. Sabens, H.B. Martin, C.A. Zorman

  Microelectromechanical Systems, Journal of.

  This paper reports the design, fabrication, and characterization of diamond-on-polymer microelectrode arrays. A “diamond-first” chemical release transfer process was implemented to integrate diamondThis paper reports the design, fabrication, and characterization of diamond-on-polymer microelectrode arrays. A “diamond-first” chemical release transfer process was implemented to integrate diamond electrodes, grown at temperatures >; 700 °C, on a temperature-sensitive polynorbornene-based (PNB) substrate, allowing for the advantageous neural interfacing properties of diamond to be utilized in a flexible device. Intracortical probes with two electrodes and peripheral nerve electrode arrays with ten electrodes ranging in area from 800 to 41 000 μm² were fabricated. Mechanical testing showed that the structures were flexible, with the composite structure having mechanical characteristics similar to bare PNB. Electrical testing confirmed that ohmic contacts were formed without a postanneal step and determined a diamond-on-polymer electrode impedance of ~ 1.5 MΩ at 1 kHz.

• Electrochemically Assisted Maskless Selective Removal of Metal Layers for Three-Dimensional Micromachined SOI RF MEMS Transmission Lines and Devices

  Authors: M. Sterner, N. Roxhed, G. Stemme, J. Oberhammer

  Microelectromechanical Systems, Journal of.

  This paper presents a novel electrochemically assisted wet-etching method for maskless selective removal of metal layers. This method has been developed as the key process step for enabling theThis paper presents a novel electrochemically assisted wet-etching method for maskless selective removal of metal layers. This method has been developed as the key process step for enabling the fabrication of low-loss 3-D micromachined silicon-on-insulator-based radio-frequency microelectromechanical systems transmission line components, consisting of a silicon core in the device layer covered by a gold metallization layer. For this application, the full-wafer sputtered metallization layer must be locally removed on the handle layer to guarantee for a well-defined and low-loss coplanar-waveguide propagation mode in the slots of the transmission line. It is not possible to use conventional photolithography or shadow masking. Gold areas to be etched are biased by a 1.2-V potential difference to a saturated calomel reference electrode in a NaCl(aq) solution. The measured etch rate of the proposed local electrochemically biased etching process is 520 nm/min, and no detectable etching was observed on unbiased areas even after a 1-h etch. The suitability of different adhesion layers has been investigated, and Ti-based adhesion layers were found to result in the highest yield. The new etching method has been successfully applied for the fabrication of transmission lines with integrated microswitches, lowering the insertion loss of the waveguide at 10 GHz from 1.3 to 0.3 dB/mm. The issue of unwanted thin metallic connections caused by secondary deposition during sputtering is discussed but found not to significantly affect the process yield. Finally, local removal of gold on isolated features even within the device layer is presented for locally removing the metallization on stoppers of laterally moving electrostatic actuators, to drastically reduce the mechanical wear on stopper tips.

• Characterization and Reduction of MEMS Sidewall Friction Using Novel Microtribometer and Localized Lubrication Method

  Authors: Hongbin Yu, Guangya Zhou, S.K. Sinha, J.Y. Leong, Fook Siong Chau

  Microelectromechanical Systems, Journal of.

  A novel microtribometer is developed to characterize microelectromechanical systems (MEMS) sidewall friction with high resolution. The design is based on a rotational grating displacement sensingA novel microtribometer is developed to characterize microelectromechanical systems (MEMS) sidewall friction with high resolution. The design is based on a rotational grating displacement sensing mechanism, with which 1.2-nm sensing sensitivity can be achieved. Employing it, the adhesion force (1.85 μN) and the coefficients of static (0.801) and kinetic (0.363) frictions on the sidewall of an as-fabricated MEMS device have been measured. Besides these, the whole process of stick-slip associated with the movement under friction, including the transition between static and kinetic frictional states, has also been clearly revealed. To reduce friction, a localized lubrication method is developed, with which liquid lubricant can be applied directly onto the desired region without affecting other components on the same device. From the experimental results, reduced values in adhesion force (1.23 μN ) and coefficients of friction (0.262 for static and 0.183 for kinetic) are obtained in the same MEMS device after lubrication treatment, demonstrating improved frictional performance.

• Photoelectric Monolayers Based on Self-Assembled and Oriented Purple Membrane Patches

  Authors: K.M. Al-Aribe, G.K. Knopf, A.S. Bassi

  Microelectromechanical Systems, Journal of.

  The fabrication of dry ultrathin photoelectric layers is described in this paper. The self-assembled monolayer of oriented purple membrane (PM) patches from bacteriorhodopsin (bR) is created on aThe fabrication of dry ultrathin photoelectric layers is described in this paper. The self-assembled monolayer of oriented purple membrane (PM) patches from bacteriorhodopsin (bR) is created on a bio-functionalized gold (Au) surface using a biotin molecular recognition technique. The biotin enables the extracellular side of the bR PMs to be accurately labeled. During the biochemical immobilization process, the biotinylated alkylthiols modify the Au surface using HS terminals of the thiols and affix the labeled bR to the functionalized surface using streptavidin-biotin interactions. An optically transparent indium tin oxide (ITO) electrode is then placed on top of the finished assembly to complete the circuit of the photocell for testing and performance verification. An experimental study shows that the proposed self-assembly method can produce a 12.33 nm thick photoelectric layer that generates nearly 0.54 mV/(mW ·cm²) when exposed to a 568-nm laser beam. In contrast, other immobilization techniques such as electric field sedimentation produce dry bR films that are more than 10 μm thick. These ultrathin photoelectric layers can be used to create nanoscale light sensors and photocells.

• Micromachining of Pyrex 7740 Glass by Silicon Molding and Vacuum Anodic Bonding

  Authors: Junwen Liu, Jintang Shang, Jieying Tang, Qing-An Huang

  Microelectromechanical Systems, Journal of.

  A wafer-level processing technology that is used to precisely fabricate regular arrays of deep cavities in a Pyrex 7740 glass wafer is presented by silicon molding and vacuum anodic bonding. TheA wafer-level processing technology that is used to precisely fabricate regular arrays of deep cavities in a Pyrex 7740 glass wafer is presented by silicon molding and vacuum anodic bonding. The fabrication process is based on etching cavities in silicon, followed by vacuum anodic bonding of a glass wafer to the etched silicon wafer. The bonded wafers are then heated inside a furnace at a temperature above the softening point of the glass, and the glass is shaped into cavities. The processing parameters are obtained by a series of experiments. The array of square glass cavities with 10-μm side length is accurately fabricated. Finally, a wafer-level hermetic packaging process is demonstrated after the second anodic bonding process. A diced single chip has been tested for leakage rate and bonding strength, which shows that the presented fabrication process is appropriate for the wafer-level packaging of MEMS devices.

• Direct Metal Transfer Lithography for Fabricating Wire-Grid Polarizer on Flexible Plastic Substrate

  Authors: Chun-Hung Chen, Te-Hui Yu, Yung-Chun Lee

  Microelectromechanical Systems, Journal of.

  This paper reports on the fabrication of polymer-based metallic wire-grid polarizers using a direct metal contact printing method. The proposed method can directly transfer a metal pattern from aThis paper reports on the fabrication of polymer-based metallic wire-grid polarizers using a direct metal contact printing method. The proposed method can directly transfer a metal pattern from a silicon mold to a soft plastic substrate simply by roller pressing and infrared (IR) heating. With properly chosen loading contact pressure and heating temperature, metallic linear grating structures with a linewidth of 60 nm, a period of 170 nm, and an area size of 2.5 ×2.5 cm² are successfully formed on the surface of a polyethylene terephtalate (PET) substrate. The optical performance of the fabricated flexible polarizers is experimentally measured and numerically analyzed in the near-IR spectrum with wavelength from 800 to 1500 nm. Inspired by the numerical simulation results, the optical characteristics of the flexibe polarizers are further enhanced by reactive ion etching on the PET substrate. Good agreements between experiments and theoretical simulation are obtained. Future developments and potential applications of this metal contact transfer lithography method will be addressed.

• MEMS Mechanical Fatigue: Effect of Mean Stress on Gold Microbeams

  Authors: G. De Pasquale, A. Soma

  Microelectromechanical Systems, Journal of.

  In this paper, the reliability of gold components for microelectromechanical systems applications is studied by evaluating the mechanical fatigue behavior. The lifetime of microspecimens underIn this paper, the reliability of gold components for microelectromechanical systems applications is studied by evaluating the mechanical fatigue behavior. The lifetime of microspecimens under alternate loads with different mean stress conditions is tested with the introduction of an original experimental procedure. Dedicated fatigue test devices are designed and fabricated with the aim of producing an alternate load on the embedded specimen. Electrostatic actuation is used as a driving force. Gold microbeams are tested under tensile variable load with different levels of mean and alternate stresses. FEM models are exploited to estimate the stress level produced in the material under the variable actuation conditions. Experimental results are analyzed to investigate the effects of different mean stress levels on lifetime under mechanical fatigue. The fatigue results are represented by a Goodman-Smith diagram scheme. Surface topography degradation is monitored through scanning electron microscope images. The modes of failure are in agreement with the literature, which is a consequence of fatigue degradation.

• Micro Power Generator for Harvesting Low-Frequency and Nonperiodic Vibrations

  Authors: T. Galchev, Hanseup Kim, K. Najafi

  Microelectromechanical Systems, Journal of.

  This paper presents a new inertial power generator for scavenging low-frequency nonperiodic vibrations called the Parametric Frequency-Increased Generator (PFIG). The PFIG utilizes three magneticallyThis paper presents a new inertial power generator for scavenging low-frequency nonperiodic vibrations called the Parametric Frequency-Increased Generator (PFIG). The PFIG utilizes three magnetically coupled mechanical structures to initiate high-frequency mechanical oscillations in an electromechanical transducer. The fixed internal displacement and dynamics of the PFIG allow it to operate more effectively than resonant generators when the ambient vibration amplitude is higher than the internal displacement limit of the device. The design, fabrication, and testing of an electromagnetic PFIG are discussed. The developed PFIG can generate a peak power of 163 μW and an average power of 13.6 μW from an input acceleration of 9.8 m/s² at 10 Hz, and it can operate at frequencies up to 65 Hz, giving it an unprecedented operating bandwidth and versatility. The internal volume of the generator is 2.12 cm³ (3.75 cm³ including the casing). The harvester has a volume figure of merit of 0.068% and a bandwidth figure of merit of 0.375%. These values, although seemingly low, are the highest reported in the literature for a device of this size and operating in the difficult frequency range of ≤ 20 Hz.

• Compact On-Chip Microtensile Tester With Prehensile Grip Mechanism

  Authors: S.S. Hazra, M.S. Baker, J.L. Beuth, M.P. de Boer

  Microelectromechanical Systems, Journal of.

  Accurate measurement of material strength at small scales is of critical importance for the design and manufacture of reliable micro- and nanoscale devices. Many materials of interest, e.g.,Accurate measurement of material strength at small scales is of critical importance for the design and manufacture of reliable micro- and nanoscale devices. Many materials of interest, e.g., polycrystalline silicon (polysilicon) and silicon carbide, are brittle, with statistical strength distributions. Therefore, strength quantification requires a large number of tests accurately performed on a practical platform. Here, analysis and testing of a compact on-chip microtensile test system, recently presented in a brief communication [Hazra et al., Journal of Micromechanics & Microengineering, 2009], is expanded significantly. We present new data on strength, alignment precision, temperature distribution, compliance calibration, stiffness ratio, force calibration, and effect of monolayer film coverage. High force (up to 30 mN) is applied to a 70-μm-long freestanding tensile bar (nominally of 2 μm width and 2.25 μm height) by cooling a thermal actuator (TA) that has gripped a crosshead via a prehensile mechanism. According to finite element analysis, specimen heating is small (<; 45°C above ambient). The system features a relatively small area occupied on the chip (500 × 700 μm²); excellent alignment resulting in in-plane and out-of-plane stress gradients of 2.2% and 1.5%, respectively, no sensitivity to residual stress or to cross-sectional shape, and high strain resolution (2.3 ×10^-4). A compliance calibration factor, obtained from finite element analysis, is used to convert measured fracture displacement to fracture strain. The grip mechanism must be much stiffer than the tensile bar. A value of 6.1 is determined for this stiffness ratio. We show that the TA acts as a nonlinear spring that can be modeled to determine the applied force. Assuming a value of Young's modulus E = 164 GPa, we find a characteristic strength of 2.45 GPa, with a Weibull modulus of 12.04, reflecting a- - sample size of N = 34 polysilicon microtensile bars.

• Separating and Detecting Escherichia Coli in a Microfluidic Channel for Urinary Tract Infection Applications

  Authors: Yongmo Yang, Sangpyeong Kim, Junseok Chae

  Microelectromechanical Systems, Journal of.

  We report a lab-on-a-chip (LOC) that can separate and detect Escherichia coli (E. coli) in simulated urine samples for urinary tract infection (UTI) applications. The LOC consists of twoWe report a lab-on-a-chip (LOC) that can separate and detect Escherichia coli (E. coli) in simulated urine samples for urinary tract infection (UTI) applications. The LOC consists of two (concentration and sensing) chambers connected in series and an integrated impedance detector. The two-chamber approach is designed to reduce the nonspecific absorption of a protein, e.g., albumin, that potentially coexists with E. coli in urine. We directly separate E. coli K-12 from cocktail urine in a concentration chamber containing microsized magnetic beads conjugated with anti-E. coli antibody. The immobilized E. coli is transferred to a sensing chamber for the impedance measurement. The measurement at the concentration chamber suffers from nonspecific absorption of albumin on the gold electrode, which may lead to false-positive response. By contrast, the measured impedance at the sensing chamber shows a ~ 60-kΩ impedance change. This is a clear distinction between 6.4 × 10⁴ and 6.4 × 10⁵ CFU/mL, covering the threshold of UTI (10⁵ CFU/mL). The sensitivity of the LOC in detecting E. coli is characterized to be at least 3.4 × 10⁴ CFU/mL. We also characterized the LOC for different age groups and white blood cell spiked samples. These preliminary data show promising potential for application in portable LOC devices for UTI detection.

• Performance and Modeling of a Fully Packaged Micromachined Optical Microphone

  Authors: M.L. Kuntzman, C.T. Garcia, A.G. Onaran, B. Avenson, K.D. Kirk, N.A. Hall

  Microelectromechanical Systems, Journal of.

  A microelectromechanical systems (MEMS) optical microphone that measures the interference of light resulting from its passage through a diffraction grating and reflection from a vibrating diaphragmA microelectromechanical systems (MEMS) optical microphone that measures the interference of light resulting from its passage through a diffraction grating and reflection from a vibrating diaphragm is described ( JASA, v. 122, no. 4, 2007). In the present embodiment, both the diffractive optical element and the sensing diaphragm are micromachined on silicon. Additional system components include a semiconductor laser, photodiodes, and required readout electronics. Advantages of this optical detection technique have been demonstrated with both omnidirectional microphones and biologically inspired directional microphones. In efforts to commercialize this technology for hearing aids and other applications, a goal has been set to achieve a microphone contained in a small surface-mount package (occupying 2 × 2 mm × 1 mm volume), with ultralow noise (20 dBA) and a broad frequency response (20 Hz-20 kHz). Such a microphone would be consistent in size with the smallest MEMS microphones available today but would have noise performance characteristics of professional-audio microphones significantly larger in size and more expensive to produce. This paper will present several unique challenges in our effort to develop the first surface-mount packaged optical MEMS microphone. The package must accommodate both optical and acoustical design considerations. Dynamic models used for simulating frequency response and noise spectra of fully packaged microphones are presented and compared with measurements performed on prototypes.

• Tungsten-Microhotplate-Array-Based Pirani Vacuum Sensor System With On-Chip Digital Front-End Processor

  Authors: Jiaqi Wang, Zhenan Tang, Jinfeng Li

  Microelectromechanical Systems, Journal of.

  An integrated CMOS-compatible Pirani vacuum sensor system has been developed in this paper, which consists of a tungsten microhotplate array with four same microhotplates in series, a constantAn integrated CMOS-compatible Pirani vacuum sensor system has been developed in this paper, which consists of a tungsten microhotplate array with four same microhotplates in series, a constant current circuit, an 8-b A/D converter, and a digital interface. With a tiny amount of the external components, a gas pressure between 10^-1 and 10⁵ Pa can be sampled, digitized, and real-time displayed by a LED. It can also be transferred to an external process unit, which makes it suitable for application in a gas pressure control system. The sensor system is implemented in a 0.5-μm CMOS process. When the sensor system works at 5-V voltage and 2.5-MHz clock input, the total power consumption is 350 mW, and the temperature increase of each microhotplate is 35°C.

• Electrical Access to Lipid Bilayer Membrane Microchambers for Transmembrane Analysis

  Authors: T. Osaki, Y. Watanabe, R. Kawano, H. Sasaki, S. Takeuchi

  Microelectromechanical Systems, Journal of.

  This letter describes the integration of an electrical connection onto a lipid bilayer membrane microchip for the electrical detection/regulation of transmembrane phenomena together with fluorescenceThis letter describes the integration of an electrical connection onto a lipid bilayer membrane microchip for the electrical detection/regulation of transmembrane phenomena together with fluorescence monitoring. Arrayed microchambers with a volume of 3 pL were fabricated within a poly(dimethyl siloxane) microfluidic device, and electrical access was achieved by designing channels adjacent to the chambers that were bridged by gold patterns on a glass substrate. We succeeded in the formation of a lipid bilayer membrane at the mouth of the chamber and applied electrical potential to the membrane with the integrated component. We confirmed the reconstitution of a transmembrane nanopore protein into the formed lipid bilayer membrane by signal monitoring with the electrical connection.

• Wafer-to-Wafer Alignment for Three-Dimensional Integration: A Review

  Authors: Sang Hwui Lee, Kuan-Neng Chen, J.J.-Q. Lu

  Microelectromechanical Systems, Journal of.

  This paper presents a review of the wafer-to-wafer alignment used for 3-D integration. This technology is an important manufacturing technique for advanced microelectronics and microelectromechanicalThis paper presents a review of the wafer-to-wafer alignment used for 3-D integration. This technology is an important manufacturing technique for advanced microelectronics and microelectromechanical systems, including 3-D integrated circuits, advanced wafer-level packaging, and microfluidics. Commercially available alignment tools provide prebonding wafer-to-wafer misalignment tolerances on the order of 0.25 μm. However, better alignment accuracy is required for increasing demands for higher density of through-strata vias and bonded interstrata vias, whereas issues with wafer-level alignment uniformity and reliability still remain. Three-dimensional processes also affect the alignment accuracy, although the misalignment could be reduced to certain extent by process control. This paper provides a comprehensive review of current research activities over wafer-to-wafer alignment, including alignment methods, accuracy requirements, and possible misalignments and fundamental issues. Current misalignment concerns of the major bonding approaches are discussed with detailed alignment results. The fundamental issues associated with wafer alignment are addressed, such as alignment mechanisms, uniformity, reproducibility, thermal mismatch, and materials. Alternative alignment approaches are discussed, and perspectives for wafer-to-wafer alignment are given.

• Oxidation of RuAl and NiAl Thin Films: Evolution of Surface Morphology and Electrical Resistance

  Authors: J.A. Howell, C.L. Muhlstein, B.Z. Liu, Q. Zhang, S.E. Mohney

  Microelectromechanical Systems, Journal of.

  RuAl and NiAl thin films on SiO₂/Si were oxidized, and the results were compared to those from aluminum, ruthenium, and nickel films. Both aluminides are more oxidation resistant thanRuAl and NiAl thin films on SiO₂/Si were oxidized, and the results were compared to those from aluminum, ruthenium, and nickel films. Both aluminides are more oxidation resistant than nickel, aluminum, and ruthenium, and they form an outer layer of alumina after oxidation to 850 °C. The depth profiles differ for NiAl and RuAl, with alternating layers of alumina and a Ru-rich phase forming on RuAl, while a more complex structure forms on NiAl due to reaction with the substrate. The surface of RuAl after oxidation remains fairly smooth and reflective, whereas NiAl has a hazy appearance. However, the surface morphology changes at a slightly lower temperature in the case of RuAl (~ 500°C) . Both films remain conductive even after the surface begins to show signs of oxidation, with the NiAl remaining conductive to a higher temperature (after 1 h at 850 °C) than RuAl. The results show that NiAl and RuAl films can be used in an oxidizing atmosphere up to ~ 500°C (at least 1 h) for applications requiring a smooth reflective surface and to higher temperatures when the surface quality is less important but conductivity needs to be maintained (~ 800°C for RuAl and ~ 850°C for NiAl).

• Predicting Fracture in Micrometer-Scale Polycrystalline Silicon MEMS Structures

  Authors: E.D. Reedy, B.L. Boyce, J.W. Foulk, R.V. Field, M.P. de Boer, S.S. Hazra

  Microelectromechanical Systems, Journal of.

  Designing reliable MEMS structures presents numerous challenges. Polycrystalline silicon fractures in a brittle manner with considerable variability in measured strength. Furthermore, it is not clearDesigning reliable MEMS structures presents numerous challenges. Polycrystalline silicon fractures in a brittle manner with considerable variability in measured strength. Furthermore, it is not clear how to use measured tensile strength data to predict the strength of a complex MEMS structure. To address such issues, two recently developed high-throughput MEMS tensile test techniques have been used to estimate strength distribution tails by testing approximately 1500 tensile bars. There is strong evidence that the micromachined polycrystalline silicon that was tested in this paper has a lower bound to its tensile strength (i.e., a strength threshold). Process-induced sidewall flaws appear to be the main source of the variability in tensile strength. Variations in as-fabricated dimensions, stress inhomogeneity within a polycrystal, and variations in the apparent fracture toughness do not appear to be dominant contributors to tensile strength variability. The existence of a strength threshold implies that there is maximum flaw size, which consequently enables a linear elastic fracture mechanics flaw-tolerance analysis. This approach was used to estimate a lower bound for the strength of a double edge-notched specimen that compared favorably with our measured values.

• High-Performance Lateral-Actuating Magnetic MEMS Switch

  Authors: M. Glickman, P. Tseng, J. Harrison, T. Niblock, I.B. Goldberg, J.W. Judy

  Microelectromechanical Systems, Journal of.

  A lateral-actuating magnetic MEMS switch has been fabricated, which generates an estimated 200 μN of magnetic closing force with less than 0.7 V of actuation voltage and 13-mW power. The switchA lateral-actuating magnetic MEMS switch has been fabricated, which generates an estimated 200 μN of magnetic closing force with less than 0.7 V of actuation voltage and 13-mW power. The switch closes in 65 μs, reaches steady state within 200 μs, and has a powerful return force of 70 μN. The contact resistance was 0.1 to 0.4 Ω and lasted 3 ·10⁶ cycles before failure. The device uses low-temperature processing (<; 300°C), low voltage, and substrate-agnostic fabrication technology that facilitates fabrication on (and integration with) a wide variety of substrates and technologies.

• Inkjet-Printed Polymeric Microstructures in -Sided Regular Polygonal Cavities

  Authors: Chin-Tai Chen, Ching-Long Chiu, Chung-Yi Hsu, Zhao-Fu Tseng, Chun-Te Chuang

  Microelectromechanical Systems, Journal of.

  We demonstrate an inkjet-based microfluidic technique as droplet vaporization deposition (DVD) that can be applied in the incorporation of hydrophobic substrates with microcavities to generateWe demonstrate an inkjet-based microfluidic technique as droplet vaporization deposition (DVD) that can be applied in the incorporation of hydrophobic substrates with microcavities to generate individual polymeric structures. Using soft-lithography method, the SU-8 and polydimethysiloxane were patterned to form various polygon-shaped cavities (side length ~200-700 μm and depth ~ 25-110 μm) which acted as micromolds (templates) for forming the shapes of the droplets deposited. With aqueous polyurethane droplets generated (single volume ~381 pL), the novel various microstructures in polygonal (tri- to hexagonal) forms were created through the deposition and evaporation processes and characterized with exotic performances in optics such as those of microlenses and micromirrors. Experimental and analytical results illustrated that the curved-surface (sinusoidal) topographies of the structures self-formed and detached from the underlying substrates were dominated by capillary action of fluid during evaporation. The merits over the existing techniques such as photolithography includes the one-step, low-temperature (ambient condition, ~1 atm at 25°C), and cost-effective (no waste materials) processes of solid formations. The successful formation of these structures suggests a new mechanism for self-releasing/detaching from the molds. As a reliable technique for the fabrication of such microstructures, the present DVD method presents an alternative method for various applications particularly including optical microelectromechanical system devices and parts used for assembly.

• Measuring Quality Factor From a Nonlinear Frequency Response With Jump Discontinuities

  Authors: W.O. Davis

  Microelectromechanical Systems, Journal of.

  The convenient half-power bandwidth formula used for measurement of quality factor Q does not apply for nonlinear systems that have jump discontinuities in their frequency responses, since one of theThe convenient half-power bandwidth formula used for measurement of quality factor Q does not apply for nonlinear systems that have jump discontinuities in their frequency responses, since one of the half-power amplitudes is not observable. This paper shows alternatives to the half-power formula that do apply to such nonlinear systems, while preserving all of the convenience of the method. Their practical use is illustrated by experimental Q measurements for a microelectromechanical systems scanning mirror.

• In Situ Fabrication and Actuation of Polymer Magnetic Microstructures

  Authors: Su Eun Chung, Jiyun Kim, Sung-Eun Choi, L.N. Kim, Sunghoon Kwon

  Microelectromechanical Systems, Journal of.

  We demonstrate a single-exposure in situ magnetic actuator fabrication technique using magnetic nanoparticles (MNs) containing UV curable polymer in a Polydimethylsiloxane (PDMS) channel.We demonstrate a single-exposure in situ magnetic actuator fabrication technique using magnetic nanoparticles (MNs) containing UV curable polymer in a Polydimethylsiloxane (PDMS) channel. Microstructures with a 3-D anchored cantilever as well as free-floating components are fabricated in a single step at a single site without the use of a sacrificial layer. By controlling the location of high oxygen concentration area through PDMS substrate patterning, we can create partially bound and free-floating movement-restricted structures. This allows us to create complex magnetic actuators, such as a 3-D anchored cantilever, motor type, and rail-guided magnetic actuators. The actuating performance of UV photopatterned magnetic microstructures depends on the MN concentration in photopolymer resin and magnetic field intensity. The measured translational velocity of magnetic microactuators with a 1 : 10 MN concentration is 140 μm/s under 1400 G of magnetic field in poly(ethylene glycol) diacrylate resin. Also, we demonstrate selective magnetic actuation of heterogeneous structures composed of magnetic and nonmagnetic parts self-assembled in railed microfluidic channels. Only magnetic parts from the assembly selectively actuated due to the magnetic field without response to the flow. Therefore, we have developed a versatile magnetic microstructure fabrication method that is very simple and fast, enabling rapid in situ fabrication and actuation.

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