Microelectromechanical Systems Platform Research Articles

MEMS reconfigurable terahertz meta-absorber with polarization-dependent and sensing characteristics

This study presents and demonstrates a design of a micro-electro-mechanical system (MEMS) reconfigurable terahertz (THz) metamaterial absorber (TMA) that shows tunable free spectra range with a maximum value as 166 GHz in transverse magnetic mode and switchable resonance from 1.24 THz to 1.53 THz. The unit structure of TMA consists of two movable rectangular resonators aside and an x-shaped resonator at the center comprising two c-shaped resonators connected upside down. The material configuration of TMA is typical of the metal–insulator-metal sandwich configuration. That is a bottom Au layer preventing the penetration of the THz wave, a dielectric SiO2 layer to accommodate and absorb the incident wave, and a patterned Au structure array to select the resonant frequency. The electromagnetic response of TMA could be flexibly modulated when the structure is reconfigured by changing the gaps between x-shaped resonators and rectangular resonators based on the MEMS platform. Meanwhile, owing to the asymmetry of resonant structure, the electromagnetic response of TMA could be tuned from single-, dual-, triple- quad-resonances by varying the polarization state of incidence. Furthermore, the sensitivity of TMA is explored and demonstrated with remarkable linearity under a variation of the surrounding environment refractive index from 1.0 to 2.0. The feasibility of TMA is validated as the experimental absorption spectra are well meet the simulation results. The above results indicate the proposed TMA possesses great potential applications in multiple resonance switches, polarization switches, and highly efficient environmental sensors.

Integrated silicon photonic MEMS

Silicon photonics has emerged as a mature technology that is expected to play a key role in critical emerging applications, including very high data rate optical communications, distance sensing for autonomous vehicles, photonic-accelerated computing, and quantum information processing. The success of silicon photonics has been enabled by the unique combination of performance, high yield, and high-volume capacity that can only be achieved by standardizing manufacturing technology. Today, standardized silicon photonics technology platforms implemented by foundries provide access to optimized library components, including low-loss optical routing, fast modulation, continuous tuning, high-speed germanium photodiodes, and high-efficiency optical and electrical interfaces. However, silicon’s relatively weak electro-optic effects result in modulators with a significant footprint and thermo-optic tuning devices that require high power consumption, which are substantial impediments for very large-scale integration in silicon photonics. Microelectromechanical systems (MEMS) technology can enhance silicon photonics with building blocks that are compact, low-loss, broadband, fast and require very low power consumption. Here, we introduce a silicon photonic MEMS platform consisting of high-performance nano-opto-electromechanical devices fully integrated alongside standard silicon photonics foundry components, with wafer-level sealing for long-term reliability, flip-chip bonding to redistribution interposers, and fibre-array attachment for high port count optical and electrical interfacing. Our experimental demonstration of fundamental silicon photonic MEMS circuit elements, including power couplers, phase shifters and wavelength-division multiplexing devices using standardized technology lifts previous impediments to enable scaling to very large photonic integrated circuits for applications in telecommunications, neuromorphic computing, sensing, programmable photonics, and quantum computing.

An 8-inch commercial aluminum nitride MEMS platform for the co-existence of Lamb wave and film bulk acoustic wave resonators

This work investigates a co-design approach for fundamental symmetric Lamb wave (S0) resonators (LWR) and film bulk acoustic wave resonators (FBAR) in a commercial 8-inch aluminum nitride (AlN) microelectromechanical system (MEMS) platform to enable multi-band operation. The platform utilizes surface micromachining to define local release cavities, providing an undercut-free solution for acoustic resonators to achieve a high quality factor (Q). However, being based on a standardized platform initially tailored for FBAR devices, many design considerations and trade-offs need to be investigated for the co-existence between LWR and FBAR design. Hence, to capture the optimal design window for S0 LWRs while analyzing its performance impact on existing FBARs, the electrode configuration and its thickness are thoroughly investigated by the finite element method. In this work, a 2.2 GHz FBAR, a 700 MHz S0 LWR, and a 2.19 GHz S0 Lamé LWR are demonstrated for performance evaluation across different types of devices in this platform. The measurement results revealed a baseline performance for the FBAR device with an electromechanical coupling factor () of 6.73% and Q of 3017 at 2.2 GHz, resulting in a high figure-of-merit (FoM = ) over 200. In comparison, the 700 MHz S0 LWR exhibits a high Q of 2532 as well and a of 1.1% (FoM = 27.8), while the 2.19 GHz S0 Lamé LWR also exhibits a high Q of 1752 and a of 2.44% (FoM = 42.7), respectively. These performance indexes are all comparable with the current state-of-the-art, revealing the excellent potential of this AlN MEMS platform being implemented for future LWR development design or even mass production.

MEMS-Based Tactile Sensors: Materials, Processes and Applications in Robotics.

Commonly encountered problems in the manipulation of objects with robotic hands are the contact force control and the setting of approaching motion. Microelectromechanical systems (MEMS) sensors on robots offer several solutions to these problems along with new capabilities. In this review, we analyze tactile, force and/or pressure sensors produced by MEMS technologies including off-the-shelf products such as MEMS barometric sensors. Alone or in conjunction with other sensors, MEMS platforms are considered very promising for robots to detect the contact forces, slippage and the distance to the objects for effective dexterous manipulation. We briefly reviewed several sensing mechanisms and principles, such as capacitive, resistive, piezoresistive and triboelectric, combined with new flexible materials technologies including polymers processing and MEMS-embedded textiles for flexible and snake robots. We demonstrated that without taking up extra space and at the same time remaining lightweight, several MEMS sensors can be integrated into robotic hands to simulate human fingers, gripping, hardness and stiffness sensations. MEMS have high potential of enabling new generation microactuators, microsensors, micro miniature motion-systems (e.g., microrobots) that will be indispensable for health, security, safety and environmental protection.

Integrated 1 × 3 MEMS silicon nitride photonics switch.

We present a 1 × 3 optical switch based on a translational microelectromechanical system (MEMS) platform with integrated silicon nitride (SiN) photonic waveguides. The fabricated devices demonstrate efficient optical signal transmission between fixed and suspended movable waveguides. We report a minimum average insertion loss of 4.64 dB and a maximum average insertion loss of 5.83 dB in different switching positions over a wavelength range of 1530 nm to 1580 nm. The unique gap closing mechanism reduces the average insertion loss across two air gaps by a maximum of 7.89 dB. The optical switch was fabricated using a custom microfabrication process developed by AEPONYX Inc. This microfabrication process integrates SiN waveguides with silicon-on-insulator based MEMS devices with minimal stress related deformation of the MEMS platform.

Improved formaldehyde gas sensing properties of well-controlled Au nanoparticle-decorated In2O3 nanofibers integrated on low power MEMS platform

Approaches for the fabrication of a low power-operable formaldehyde (HCHO) gas sensor with high sensitivity and selectivity were performed by the utilization of an effective micro-structured platform with a micro-heater to reach high temperature with low heating power as well as by the integration of indium oxide (In2O3) nanofibers decorated with well-dispersed Au nanoparticles as a sensing material. Homogeneous In2O3 nanofibers with the large specific surface area were prepared by the electrospinning following by calcination process. Au nanoparticles with the well-controlled size as a catalyst were synthesized on the surface of In2O3 nanofibers. The Au-decorated In2O3 nanofibers were reliably integrated as sensing materials on the bridge-type micro-platform including micro-heaters and micro-electrodes. The micro-platform designed to maintain high temperature with low power consumption was fabricated by a microelectromechanical system (MEMS) technique. The micro-platform gas sensor consisting with Au-In2O3 nanofibers were fabricated effectively to detect HCHO gases with high sensitivity and selectivity. The HCHO gas sensing behaviors were schematically studied as a function of the gas concentration, the size of the adsorbed Au nanoparticles, the applied power to raise the temperature of a sensing part and the kind of target gases.

Translational MEMS Platform for Planar Optical Switching Fabrics.

While 3-D microelectromechanical systems (MEMS) allow switching between a large number of ports in optical telecommunication networks, the development of such systems often suffers from design, fabrication and packaging constraints due to the complex structures, the wafer bonding processes involved, and the tight alignment tolerances between different components. In this work, we present a 2-D translational MEMS platform capable of highly efficient planar optical switching through integration with silicon nitride (SiN) based optical waveguides. The discrete lateral displacement provided by simple parallel plate actuators on opposite sides of the central platform enables switching between different input and output waveguides. The proposed structure can displace the central platform by 3.37 µm in two directions at an actuation voltage of 65 V. Additionally, the parallel plate actuator designed for closing completely the 4.26 µm air gap between the fixed and moving waveguides operates at just 50 V. Eigenmode expansion analysis shows over 99% butt-coupling efficiency the between the SiN waveguides when the gap is closed. Also, 2.5 finite-difference time-domain analysis demonstrates zero cross talk between two parallel SiN waveguides across the length of the platform for a 3.5 µm separation between adjacent waveguides enabling multiple waveguide configuration onto the platform. Different MEMS designs were simulated using static structural analysis in ANSYS. These designs were fabricated with a custom process by AEPONYX Inc. (Montreal, QC, Canada) and through the PiezoMUMPs process of MEMSCAP (Durham, NC, USA).

Design and fabrication of a MEMS-based gas sensor containing WO3 sensitive layer for detection of NO2

A gas sensor based on microelectromechanical systems (MEMS) technology containing a WO3 sensitive layer was designed, simulated, and fabricated. The gas sensor consists of a silicon substrate, a platinum microheater, gold interdigitated electrodes, and a WO3 sensitive layer. The active area with dimensions of 0.4 mm×0.4 mm is located at the center of a sensor (3 mm×3 mm). The experimental results show that the microheater provided heating for the WO3 sensitive layer at low power consumption and accurate temperature control. At a power consumption of only 40 mW, the temperature reached 319°C at the center of the MEMS platform with uniform heating. In addition to that, the above mentioned gas sensor exhibited a high response to NO2 with optimized sensitivity recorded at the working temperature of 170°C. With 10 ppb of NO2, the response of the sensor could reach up to 5.8 and the power consumption is 17.2 mW.

Microelectromechanical System-Based Sensing Arrays for Comparative in Vitro Nanotoxicity Assessment at Single Cell and Small Cell-Population Using Electrochemical Impedance Spectroscopy.

The traditional in vitro nanotoxicity assessment approaches are conducted on a monolayer of cell culture. However, to study a cell response without interference from the neighbor cells, a single cell study is necessary; especially in cases of neuronal, cancerous, and stem cells, wherein an individual cell's fate is often not explained by the whole cell population. Nonetheless, a single cell does not mimic the actual in vivo environment and lacks important information regarding cell communication with its microenvironment. Both a single cell and a cell population provide important and complementary information about cells' behaviors. In this research, we explored nanotoxicity assessment on a single cell and a small cell population using electrochemical impedance spectroscopy and a microelectromechanical system (MEMS) device. We demonstrated a controlled capture of PC12 cells in different-sized microwells (to capture a different number of cells) using a combined method of surface functionalization and dielectrophoresis. The present approach provides a rapid nanotoxicity response as compared to other conventional approaches. This is the first study, to our knowledge, which demonstrates a comparative response of a single cell and small cell colonies on the same MEMS platform, when exposed to metaloxide nanoparticles. We demonstrated that the microenvironment of a cell is also accountable for cells' behaviors and their responses to nanomaterials. The results of this experimental study open up a new hypothesis to be tested for identifying the role of cell communication in spreading toxicity in a cell population.

Mask-less deposition of Au–SnO2 nanocomposites on CMOS MEMS platform for ethanol detection

Here we report on the mask-less deposition of Au–SnO2 nanocomposites with a silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) micro electro mechanical system (MEMS) platform through the use of dip pen nanolithography (DPN) to create a low-cost ethanol sensor. MEMS technology is used in order to achieve low power consumption, by the employment of a membrane structure formed using deep reactive ion etching technique. The device consists of an embedded tungsten micro-heater with gold interdigitated electrodes on top of the SOI membrane. The tungsten micro-heater is used to raise the membrane temperature up to its operating temperature and the electrodes are used to measure the resistance of the nanocomposite sensing layer. The CMOS MEMS devices have high electro-thermal efficiency, with 8.2 °C temperature increase per mW power of consumption. The sensing material (Au–SnO2 nanocomposite) was synthesised starting from SnO nanoplates, then Au nanoparticles were attached chemically to the surface of SnO nanoplates, finally the mixture was heated at 700 °C in an oven in air for 4 h. This composite material was sonicated for 2 h in terpineol to make a viscous homogeneous slurry and then ‘written’ directly across the electrode area using the DPN technique without any mask. The devices were characterised by exposure to ethanol vapour in humid air in the concentration range of 100–1000 ppm. The sensitivity varied from 1.2 to 0.27 ppm−1 for 100–1000 ppm of ethanol at 10% relative humid air. Selectivity measurements showed that the sensors were selective towards ethanol when they were exposed to acetone and toluene.

Tension tests on mammalian collagen fibrils.

A brief overview of isolated collagen fibril mechanics testing is followed by presentation of the first results testing fibrils isolated from load-bearing mammalian tendons using a microelectromechanical systems platform. The in vitro modulus (326 ± 112 MPa) and fracture stress (71 ± 23 MPa) are shown to be lower than previously measured on fibrils extracted from sea cucumber dermis and tested with the same technique. Scanning electron microscope images show the fibrils can fail with a mechanism that involves circumferential rupture, whereas the core of the fibril stays at least partially intact.

Microwave MEMS Antenna Sensor Characterization and Target Detection Using Artificial Neural Networks

This paper demonstrates microwave antenna sensors fabricated on a silicon micro electro-mechanical-system (MEMS) platform. The antennas are designed to operate between 10-16 GHz with 41% bandwidth and 50 Ω input impedance. Each antenna sensor is comprised of two planar metallic four point leaves in horizontal and vertical directions providing dual linear polarization. The design is simulated using the Ansoft high frequency structure simulator. The antennas are fed using coplanar waveguide routed on top of 100 μm width silicon hinges. The fabricated MEMS platform show maximum rotation of 9.14° (total range of 18.28°) around two axes using four torsion hinges. The results highlight the limitation of silicon as hinge material when larger angles are desired. The antenna sensors demonstrate good detection of targets using measured scattered data and the artificial neural networks technique.

Piezoresistive effect of individual electrospun carbon nanofibers for strain sensing

Piezoresistive behavior of individual electrospun carbon nanofibers (CNF) was studied for the first time via a microelectromechanical systems platform. The gage factor of CNFs was found to vary from 1.96 to 2.55, not correlating with nanofiber diameter. The measured strain sensitivity of electrical resistance of individual CNFs could not be solely explained based on strain induced dimensional changes of CNFs, pointing to piezoresistivity in nanofibers. The microstructure of CNFs was studied via TEM imaging and Raman spectroscopy, suggesting the presence of sp2 and sp3 hybridized carbon atoms in CNFs. The piezoresistivity of CNFs was explained in light of their hybrid structure. A one-dimensional model was adopted to relate CNFs piezoresistivity to their microstructure and electron tunneling between sp2 hybridized regions through sp3 hybridized regions. The calibrated model revealed tunneling distances of 0.15–0.3nm between sp2 hybridized atoms. Moreover, our study pointed to the degree of graphitization and elastic mismatch between differently hybridized carbon atom regions in CNFs as critical parameters controlling CNFs’ piezoresistivity. This study sets the stage for the utilization of CNFs, not just as load bearing elements, but also as multifunctional nanoscale components with strain sensing capabilities, for instance in Nanoelectro-mechanical systems applications.

Room Temperautre Hydrogen Detection with the Use of Engineered Nanostrutured Tinoxide Array

In the forefront of the challenges that are faced by the ensuing energy crisis; alternative fuel source such as hydrogen appear to be a viable substitute. All hydrogen gas related processes require accurate monitoring for leaks during storage and transportation.The common problem that arises with the use of hydrogen is its inclination to leak along with its intrinsic capability of being highly flammable/explosive at 4 vol%. Precisely monitoring hydrogen during storage becomes imperative in industrial and general consumer applications in order to reduce the occurrence of accidents. The current sensor market includes the use of many different metal oxide sensors for use as hydrogen detectors. These chemical-resistors (chemi-resistors) function based upon the changes in conductivity due to gases chemical interaction with the sensing materials. The deficiency in most of the current metal oxide based chemi-resistors in use as detectors is that they are only applicable at elevated temperature (above 100 degree Celsius); this aids the sensor’s response kinetics by enhance kinetic interaction between gases and detector. This becomes both a safety concern due to its proximity to the highly explosive gas and also energetically inefficient. Therefore our research endeavor is to develop a low temperature, highly sensitive and robust hydrogen gas detector that operates at room temperature.Thin film SnO2 samples were deposited on SiO2/Si substrates through a method of pulse laser deposition (PLD). Nano-architectured SnO2 arrays were design with the use of nanosecond pulse laser interference irradiation of the thin films. The SnO2 nanostructures fabricated were uniformly distributed along the surface of the substrate. Dimensions of the nanostructure were obtained through atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results show that the nanoarray’s were ~8 nm in cross-sectional height and microns in length.Tests of chemi-resistors were conducted at room temperature within the concentration limits of 300 to 9000 ppm under dynamic flow in order to simulate the actual environments that the device will experience. In comparison to SnO2 thin film, SnO2 nanostructured film illustrates a significantly larger drop in conductivity upon exposure to minimal concentrations such as 600 ppm. The nanostructured film exhibited (reduced resistances by 2 orders of magnitude) ~150 fold increase in electrical response (the ratio of resistance in hydrogen to the resistance in air). Calculations show that the increase is performance of the sensor is not proportional to the increase in surface area of the nanostructured array Theoretical calculation of the potential barrier generated through exposure to hydrogen enables the improved response by increasing the depth of the depletion layer. This depletion layer (volume of SnO2 at which electrons have been strip from the conduction band) is increased in the nanostructured array hence generates larger electrical responses.Nanostructured SnO2’s incorporation into a microelectromechanical system platform has successfully produced a low temperature hydrogen gas sensor. The performance of the nano-architectured SnO2 showed improved detection capability and promising applicability due to it fast response time, high electrical response and robustness. This research endeavor therefore combines aspect of interdisciplinary design and integration alongside the creation of microelectromechanical system that is capable of being applied to today’s market.

Design of a bent beam electrothermal actuator for in situ tensile testing of ceramic nanostructures

Abstract A necessary condition to include nanoscale materials in the design of high-performing as well as reliable electrical and electromechanical devices is the availability of a sufficiently deep knowledge of their mechanical behavior. Up to date, the most powerful tools for mechanical characterization of nanosamples are properly designed microelectromechanical systems (MEMS), due to their compatibility with scanning/transmission electron microscopy (SEM/TEM) and high resolution force/displacement measurements. Herein, we report about the design of a MEMS platform for in situ SEM tensile testing of nanoscale samples. This is characterized by a very compact structure, based only on a bent beam electrothermal actuator, which performs both actuating and sensing functions. The size of the structural components of the present device is chosen with the aim of testing ceramic nanowires, but the resulting configuration can be applied also for other material samples.

A MEMS platform for in situ, real-time monitoring of electrochemically induced mechanical changes in lithium-ion battery electrodes

We report the first successful demonstration of an optical microelectromechanical systems (MEMS) sensing platform for the in situ characterization of electrochemically induced reversible mechanical changes in lithium-ion battery (LIB) electrodes. The platform consists of an array of flexible membranes with a reflective surface on one side and a thin-film LIB electrode on the other side. The membranes deflect due to the active battery material volume change caused by lithium intercalation (expansion) and extraction (contraction). This deflection is monitored using the Fabry–Perot optical interferometry principle. The active material volume change causes high internal stresses and mechanical degradation of the electrodes. The stress evolution observed in a silicon thin-film electrode incorporated into this MEMS platform follows a ‘first elastic, then plastic’ deformation scheme. Understanding of the internal stresses in battery electrodes during discharge/charge is important for improving the reliability and cycle lifetime of LIBs. The developed MEMS platform presents a new method for in situ diagnostics of thin-film LIB electrodes to aid the development of new materials, optimization of electrode performance, and prevention of battery failure.

Fabrication and testing of a MEMS platform for characterization of stimuli-sensitive hydrogels

A microelectromechanical systems (MEMS) platform for hydrogel benchmarking was designed, fabricated and tested. This MEMS platform is a testbed for the characterization of stimuli-sensitive hydrogels at the micrometer scale, which makes it a useful tool for developing and benchmarking different hydrogels in a realistic usage environment. The platform allows the application of chemical and thermal stimuli and the monitoring of the hydrogel’s swelling or shrinking by visual methods as well as by an embedded conductometric sensing mechanism. Such a platform allows measurements on a small scale and is especially useful to make a realistic assessment of the behavior of a gel after going through a microfabrication process. Several hydrogels were tested utilizing this proposed MEMS platform to prove the concept.

Compact MEMS-driven pyramidal polygon reflector for circumferential scanned endoscopic imaging probe

A novel prototype of an electrothermal chevron-beam actuator based microelectromechanical systems (MEMS) platform has been successfully developed for circumferential scan. Microassembly technology is utilized to construct this platform, which consists of a MEMS chevron-beam type microactuator and a micro-reflector. The proposed electrothermal microactuators with a two-stage electrothermal cascaded chevron-beam driving mechanism provide displacement amplification, thus enabling a highly reflective micro-pyramidal polygon reflector to rotate a large angle for light beam scanning. This MEMS platform is ultra-compact, supports circumferential imaging capability and is suitable for endoscopic optical coherence tomography (EOCT) applications, for example, for intravascular cancer detection.

Study on the Micro-Heater Geometry in In2O3 Micro Electro Mechanical Systems Gas Sensor Platforms and Effects on NO2 Gas Detecting Performances

Micro electro mechanical systems (MEMS) platforms for gas sensing devices with the co-planar type micro-heaters were designed, fabricated and its effects on the In2O3 gas sensors were investigated. Micro-heaters in MEMS gas sensor platforms were designed in the four-type heater patterns with different geometries. Electro-thermal characterizations showed that the designed platforms had highly thermal efficiency because the micro hot-plate structures were formed in the diaphragm and the thermal efficiencies were analyzed for all of 16 models and compared with each other, respectively. The designed micro-platforms were fabricated by MEMS process, and Indium oxide (In2O3) nanoparticles were synthesized by sol-gel process and dropped on the MEMS platforms for detecting the noxious oxide gas (NO2) Fabricated micro-platforms had a very low power consumption in the fabricated 16-type models, especially, the minimum power consumption was 41 mW at the operating temperature of 250 degrees C. After experiments on gas sensing characteristics to NO2 gases, fabricated In2O3 gas sensors had almost the same gas sensitivity (Rs) at the operation temperature of 250 degrees C. It is concluded that the micro-heater geometries, pattern shapes and sizes, can be influential on the power consumption of the devices and its gas sensing characteristics.

A 2 Degree-of-Freedom SOI-MEMS Translation Stage With Closed-Loop Positioning

This paper presents the design, analysis, fabrication, and characterization of a closed-loop XY micropositioning stage. The stage design is based on a 2 degree-of-freedom parallel kinematic mechanism with linear characteristics. Integrated with sensing combs, and fabricated in SOI wafers, the design provides a promising pathway to closed-loop positioning microelectromechanical systems platform with applications in nanomanufacturing and metrology. The XY stage provides a motion range of 20 micrometers in each direction at the driving voltage of 100 V. The resonant frequency of the XY stage under ambient conditions is 600 Hz. The positioning loop is closed using a capacitance-to-voltage conversion IC and a feedback controller is used to control position with an uncertainty characterized by a standard distribution of 5.24 nm and a closed-loop bandwidth of about 30 Hz.