Microelectromechanical Structure Research Articles

Sensitivity Enhancement of Tube-Integrated MEMS Flow Sensor Using Flexible Copper on Polyimide Substrate.

A tube-integrated flow sensor is proposed in this study by integrating a micro-electro mechanical systems (MEMS) flow-sensing element and electrical wiring structure on the same copper on polyimide (COP) substrate. The substrate was rolled into a circular tube with the flow-sensing element installed at the center of the tube. The signal lines were simultaneously formed and connected to the Cu layer of the substrate during the fabrication of the sensing structure, thus simplifying the electrical connection process. Finally, by rolling the fabricated sensor substrate, the flow sensor device itself was transformed into a circular tube structure, which defined the airflow region. By implementing several slits on the substrate, the sensing element was successfully placed at the center of the tube where the flow velocity is maximum. Compared to the conventional sensor structure in which the sensor was placed on the inner wall surface of the tube, the sensitivity of the sensor was doubled.

Microelectromechanical Transducer to Monitor High-Doses of Nuclear Irradiation.

This paper reports the design, fabrication and measured performance of a passive microelectromechanical transducer for the wireless monitoring of high irradiation doses in nuclear environments. The sensing device is composed of a polymer material (high-density polyethylene) sealed inside a cavity. Subjected to ionizing radiation, this material releases various gases, which increases the pressure inside the cavity and deflects a dielectric membrane. From the measurement of the deflection, the variation of the applied pressure can be estimated, and, in turn, the dose may be determined. The microelectromechanical structure can also be used to study and validate the radiolysis properties of the polymer through its gas emission yield factor. Measurement of the dielectric membrane deflection is performed here to validate on the one hand the required airtightness of the cavity exposed to doses about 4 MGy and on the other hand, the functionality of the fabricated dosimeter for doses up to 80 kGy. The selection of appropriate materials for the microelectromechanical device is discussed, and the outgassing properties of the selected high-density polyethylene are analysed. Moreover, the technological fabrication process of the transducer is detailed.

Temperature stable rare earth magnetic powder Sm-Fe-N based micro magnets with remanence enhanced by easy axis alignment and its application in MEMS actuator

In this paper, we report an actuator with a magnet made of novel rare earth magnetic powder Sm-Fe-N with diameter of 2 µm to 5 µm. Micro magnets were fabricated by mixing the magnetic powder with wax at temperature of 90 °C. Alignment of the easy axis process was employed to enhance the remanence of the micro magnets. A 8 T strong pulse magnetic field was utilized to magnetize the micro magnets. The properties of magnetic powder were revealed with vibrating sample magnetometer by measuring micro magnets with various magnetic powder weight loading percentages. In the best condition, the remanence reaches 0.9 T and the energy product reaches 70 kJ m−3. After that, the electromagnetic actuator was fabricated by embedding the magnetic powder in deep-reactive-ion-etched Si cavity with wax binder and parylene capping. The completed microelectromechanical system structure was mounted on a four-layer printed circuit board with embedded coils. Upon the application of a direct current for actuation, a displacement of 180 μm was obtained from a device volume of only 1.5 mm3 with a low actuation power consumption of 11.5 mW.

Modeling of a High-Frequency Microelectromechanical X-Band Switch for Space Applications

The results of modeling of microwave and mechanical characteristics of an X-band switch based on the technology of high-frequency microelectromechanical structures are presented. A method for design of a device operating directly in the external environment and a device whose moving components are placed in a dielectric case. Characteristics of the optimized switches are determined. Estimated mechanical calculations confirming high stability of the developed high-frequency microelectromechanical structure switches in the temperature range specific of devices used in the space industry are also performed.

MEMS sensor array-based electronic nose for breath analysis—a simulation study

The paper presents a simulation study of breath analysis based on theoretical models of microelectromechanical structure (MEMS) cantilever sensor array. The purpose of this study is to suggest a methodology for the development of MEMS electronic nose (e-nose) for monitoring disease-specific volatiles in exhaled breath. Oxidative stress and diabetes are taken as case studies for the assessment of e-nose designs. The detection of ethane for general oxidative stress, isoprene for hypoxia, and acetone for diabetes are considered for targeted detection. A number of volatiles concurrently present in the exhaled breath are taken as interferents. The MEMS cantilevers are coated with volatile-selective polymers and are analyzed in both the static and dynamic modes. The sensor array is defined by polymer selections based on three data mining methods: principal component analysis (PCA), fuzzy c-means clustering (FCM), and fuzzy subtractive clustering (FSC). This utilizes vapor/polymer partition coefficients as a database. Analyses are carried out to find optimal combinations of the polymer selection method and cantilever sensing mode. Virtual breath analysis experiments are analyzed by PCA for target discrimination. It is found that no single combination works best in all conditions. The acetone (diabetes) detection is best in both sensing modes with the polymers selected by FSC; the isoprene (hypoxia) is detectable only in static sensing mode with polymers selected by FCM clustering; and the ethane (oxidative stress) detection is possible by all sensing modes and polymer selections, provided the breath samples are preconcentrated. This study suggests that it is difficult to realize a single general-purpose MEMS breath analyzer. The dedicated analyzers for specific disease indications can however be made with an optimal combination of sensing mode and polymer coatings.

Investigation of DNA sequencing droplet trajectory observation and analysis

In this study, DNA sequencing droplet trajectories are observed and analyzed using an application-specific integrated circuit system and a micro-electromechanical system structure jetting chip. We investigate a droplet jetting technique and apply it to biomedical test chips. This use of a sprayed chip structure can reduce sequencing time by two-thirds compared with traditional methods. The structure is a three-dimensional, multi-channel drive system that can control droplets more precisely. The circuit's input control signal was generated and placed on a chip based on the quantitative design of liquid droplets. Delay time and frequency were used to set the LED light sources. In this study, we would use frequencies of 4 kHz, 8 kHz, and 12 kHz combined with two groups of different orifices and frequencies for ink droplet outlet velocity.

The oscillating and electrostatic characteristics of microelectromechanical system cantilever structure analyzed based on the air gap domain

Extensive modeling and simulation of the damping phenomenon, electrostatic actuation, and structural vibration analysis are performed. The governing partial differential equations of cantilever plate are obtained, and the resonant frequencies are calculated from the equilibrium equations. The damping forces of squeeze film are analyzed by obtaining the damping ratio and spring constant. Electrostatic actuation is applied to oscillate the cantilever to ensure that the displacement of the plate is above the thermal noise floor. Electrostatic actuating forces, displacement, and capacitance are calculated both numerically and analytically from the Poisson’s equations. Squeeze film damping effects naturally occur if structures are subjected to loading situations such that a very thin film of fluid is trapped within structural joints, interfaces, etc. An accurate estimate of squeeze film effects is important to predict the performance of dynamic structures. Squeeze film effects are simulated by the finite element method. The accuracy of the compact model is studied by comparing its response to the numerical results calculated with the finite element method. The agreement is very good in a wide frequency band. The numerical study and the compact model are directly applicable in predicting the damping force and damping factors of squeeze film.

Wavelength-Swept VCSELs

The ability to continuously tune the wavelength of a laser is of critical importance and is a fundamental building block for many optical systems, including wavelength division multiplexed optical fiber communication systems. Vertical cavity surface emitting laser (VCSEL) structure offers a unique advantage to engineer the lasing wavelength because of its ultrashort cavity length, inherently supporting a single Fabry–Perot mode. Hence, a continuous change in VCSEL cavity thickness leads to a continuous sweep of VCSEL wavelength. Wavelength-tunable VCSELs have been a subject of intense interest for the last two decades. Incorporating part or entire top mirror of a VCSEL in an optical microelectromechanical structure (MEMS), continuous wavelength sweeps have been reported. The monolithic integration brings together the best of both technologies and leads to an unprecedented performance in the continuously swept wavelength range. In addition, with the advances of ultrathin high contrast gratings and metastructures (HCG/HCM), the wavelength tuning speed of MEMS-VCSELs has been increased to 1–10 MHz range. Such lasers, now referred as wavelength-swept lasers, are enabling new applications in optical coherent tomography and light detection and ranging systems. In this paper, we review various structures and recent progress of MEMS-VCSELs. We summarize some of the early breakthroughs in designs and properties of micromechanical tunable VCSELs, including advances in HCG/HCM-based MEMS-VCSELs emitting at 850, 1060, and 1550 nm wavelength regimes. In addition, we report a brand new design leading to a record high Δλ/λo = 6.9% tuning ratio with 600 kHz speed at center wavelength of 1060 nm.

Low-voltage shock-mitigated micro-electromechanical systems structure

We report a low-voltage, yet effective, micro-electromechanical systems (MEMS) structure capable of mitigating external mechanical disturbances, such as a physical shock. External shock onto MEMS devices can be catastrophic as a conventional single membrane may travel beyond stable oscillatory distances under shock and become irreparably damaged. However, the simple addition of a second membrane on top of the single membrane drastically reduces oscillatory distances by electrostatically holding the bottom membrane within stable oscillation. The added elements, in conjunction with a fine-control algorithm, mitigate the impact of a mechanical shock onto the MEMS device. From experimental findings, it is found that the dual-membrane structure effectively reduces the travel distance of the bottom membrane by 41.5%, upon deploying merely 0.565 V onto the additional membrane. The dynamic implementation of the shock mitigation method, using an on-board accelerometer as a trigger, delivered in-situ mitigation of shock on a dual-membrane MEMS structure.

The Implementation of a High-Frequency Radio Frequency Identification System with a Battery-Free Smart Tag for Orientation Monitoring

Energy-harvesting passive RFID (radio frequency identification) tags provide countless possibilities as so-called smart tags. Smart tags can communicate with existing RFID readers or interrogators while providing a battery-less platform for internal and external sensors to enrich available information about the environment and smart tag it. A reduced cost and size as well as an increased lifespan and durability of battery-free smart tags offer improvements in areas such as transportation and product tracking. Battery-free smart tags can ideally support arbitrarily complex sensor measurements, but in reality energy limitations can introduce great reductions in operating range and thus application range. In this work, we present an example application of a smart tag with a passive HF (high-frequency) RFID tag IC (integrated circuit) and MEMS (micro electro-mechanical structure) sensor. A standard HF RFID reader connected to a PC (personal computer) allowed the RF (radio frequency) field to power and communicate with the smart tag. A Kalman filter, implemented on a PC, was used to correct and improve the raw sensor data of smart tag orientation. Measurement results showed that the MEMS sensor on the smart tag could be powered for continuous operation and that raw smart tag orientation data could be read while in the RF field of a standard HF RFID reader, but at a limited range.

Fabrication and Characterization of an MOEMS Gyroscope Based on Photonic Bandgap Materials

This paper focuses on a micro-optoelectro-mechanical vibratory gyroscope that provides an optical output and operates in a resonant condition. A custom fabrication technology, based on a silicon-on-insulator substrate, has been considered for the development of the inertial sensor. The optical readout has been accomplished using a metal–dielectric multilayer photonic bandgap (PBG) material. Such an optical structure, composed of alternated layers of one metal and one dielectric material, is embedded in the micromachined device, thus obtaining reflection properties correlated with the displacement of the proof mass induced by the external angular velocity. The principle of the micromachined gyroscope is first introduced, and then, the microelectromechanical gyroscope structure, the materials properties, and the fabrication technology are illustrated. Numerical analyses have also been performed in order to gain insight into the micromachined device. Furthermore, the optical transduction principle that exploits metal–dielectric 1-D PBG structures has been investigated from both a theoretical and an experimental point of view.

High speed optical phased array using high contrast grating all-pass filters.

We report a high speed 8x8 optical phased array using tunable 1550 nm all-pass filters with ultrathin high contrast gratings (HCGs) as the microelectromechanical-actuated top reflectors. The all-pass filter design enables a highly efficient phase tuning (1.7 π) with a small actuation voltage (10 V) and actuation displacement of the HCG (50 nm). The microelectromechanical HCG structure facilitates a high phase tuning speed >0.5 MHz. Beam steering is experimentally demonstrated with the optical phased array.

Directional acoustic response of a silicon disc‐based microelectromechanical systems structure

A microelectromechanical systems (MEMS)-based structure capable of operating mechanically as a directional acoustical sensor is presented. The structure, fabricated through the commercially available SOIMUMPS foundry process, consists of two circular discs attached to a central suspension beam, fixed at both ends. The design of the structure resembles other directional MEMS microphones that mimic the directional hearing organ of the parasitoid fly, Ormia ochracea. Modal analysis and mechanical acoustic directionality analysis using both laser Doppler vibrometry and finite element modelling have been implemented. It is demonstrated that this coupled MEMS structure exhibits an acoustic directional response, with a one-to-one relationship between the relative vibration amplitudes of the two coupled discs and the angle of sound, from −75° to +60°.

Preparation of sacrificial layer for MEMS devices by lift-off technology

To simplify the preparation of sacrificial layer in micro-electromechanical system structure, new processes have been developed. By using lift-off technology, sacrificial layer was selectively deposited into the pit that prepared for sacrificial layer releasing. Then a short time polishing process was used to remove the burrs around the pit. This method offers several advantages including reducing the difficulty of polishing and hence processing cost. Methods and apparatuses to provide a continuously smoothly sacrificial layer surface in the pit were disclosed. However, it is important to control the homogeneity of filling and avoid the shadow effect at the corner of the pit. The unpadded regions would form a steep step and cause the cracking of structure layer. This problem was discussed and solved by rotating the tilted wafer during sacrificial material deposition. The surface roughness after the preparation process of sacrificial layer was measured. The root mean square roughness of sacrificial layer was 1.247 nm and reduced to 0.861 nm after a short time polishing process. Finally, a film bulk acoustic wave resonator with stacked Mo/AlN/Mo films had been fabricated on the sacrificial layer based on this method.

Estimation of thermo-elastic damping of vibrations in micro-electro-mechanical systems resonators: finite element modeling

The authors investigated finite element (FE) analysis of damped modal vibrations in complex geometries of micro-electromechanical (MEM) resonators. Q-factor values were determined by taking the thermo-elastic damping into account. The basic model created is presented as a system of partial differential equations, which describe the elastic and thermal phenomena in the MEM structure. Mathematically the problem is formulated as a complex eigenvalue problem. Modal properties of square- and ring-shaped bulk-mode MEM resonators were investigated by taking into account the layered structure of the MEM system and the influence of the geometry of the clamping zone. The calculations were performed by employing the COMSOL Multiphysics FE software. The solution method was verified by comparing numerically and analytically obtained damped modal properties of a MEM cantilever resonator.

Effects of etching holes on complementary metal oxide semiconductor–microelectromechanical systems capacitive structure

Etching the large area of sacrificial layer under the microstructure to be released is a common method used in microelectromechanical systems technology. In order to completely release the microstructures, many etching holes are often required on the microstructure to enable the etchant to completely etch the sacrificial layer. However, the etching holes often alter the electromechanical properties of the micro devices, especially capacitive devices, because the fringe fields induced by the etching holes can significantly alter the electrical properties. This article is aimed at evaluating the fringe field capacitance caused by etching holes on microstructures. The authors aim to find a general capacitance compensation formula for the fringe capacitance of etching holes by the use of ANSYS simulation. According to the simulation results, the design of a capacitive structure with small etching holes is recommended to prevent an extreme capacitance decrease. In conclusion, this article provides a fringing field capacitance estimation method that shows the capacitance compensation tendency of the design of etching holes; this method is expected to be applicable to the design in capacitive devices of complementary metal oxide semiconductor–microelectromechanical systems technology.

Glass polarization induced drift in microelectromechanical capacitor

We present a quantitative physical model for glass substrate polarization and study the glass polarization by measuring the capacitance drift from microelectromechanical capacitor test structure. The model consists of mobile and immobile charge species, which are related to alkali metals and non-bridging oxygen in glass. The model explains consistently our results and the previously observed non-homogeneous charging effect in a radio-frequency switch fabricated on a glass substrate. The results indicate that the bulk properties of the glass layer itself can be a significant source of drift. The modeling allows estimation of the drift behavior of the several kinds of device structures.

Nanodevices: Location of Biomarkers and Reagents within Agarose Beads of a Programmable Nano‐bio‐chip (Small 5/2011)

AbstractThe slow development of cost‐effective medical microdevices with strong analytical performance characteristics is due to a lack of selective and efficient analyte capture and signaling. The recently developed programmable nano‐bio‐chip (PNBC) is a flexible detection device with analytical behavior rivaling established macroscopic methods. The PNBC system employs ≈300 μm‐diameter bead sensors composed of agarose “nanonets” that populate a microelectromechanical support structure with integrated microfluidic elements. The beads are an efficient and selective protein‐capture medium suitable for the analysis of complex fluid samples. Microscopy and computational studies probe the 3D interior of the beads. The relative contributions that the capture and detection of moieties, analyte size, and bead porosity make to signal distribution and intensity are reported. Agarose pore sizes ranging from 45 to 620 nm are examined and those near 140 nm provide optimal transport characteristics for rapid (<15 min) tests. The system exhibits efficient (99.5%) detection of bead‐bound analyte along with low (≈2%) nonspecific immobilization of the detection probe for carcinoembryonic antigen assay. Furthermore, the role analyte dimensions play in signal distribution is explored, and enhanced methods for assay building that consider the unique features of biomarker size are offered.

Location of biomarkers and reagents within agarose beads of a programmable bio-nano-chip.

The slow development of cost-effective medical microdevices with strong analytical performance characteristics is due to a lack of selective and efficient analyte capture and signaling. The recently developed programmable bio-nano-chip (PBNC) is a flexible detection device with analytical behavior rivaling established macroscopic methods. The PBNC system employs ≈300 μm-diameter bead sensors composed of agarose "nanonets" that populate a microelectromechanical support structure with integrated microfluidic elements. The beads are an efficient and selective protein-capture medium suitable for the analysis of complex fluid samples. Microscopy and computational studies probe the 3D interior of the beads. The relative contributions that the capture and detection of moieties, analyte size, and bead porosity make to signal distribution and intensity are reported. Agarose pore sizes ranging from 45 to 620 nm are examined and those near 140 nm provide optimal transport characteristics for rapid (<15 min) tests. The system exhibits efficient (99.5%) detection of bead-bound analyte along with low (≈2%) nonspecific immobilization of the detection probe for carcinoembryonic antigen assay. Furthermore, the role analyte dimensions play in signal distribution is explored, and enhanced methods for assay building that consider the unique features of biomarker size are offered.

Displacement Sensing With a Mechanically Tunable Photonic Crystal

We demonstrate a mechanically tunable photonic crystal (PC) designed for highly position-sensitive reflection. Our device consists of a multilayer PC membrane attached to a silicon microelectromechanical system structure for lateral actuation. Inside each of the PC holes there is a pillar, which is attached to the substrate. By moving the PC membrane with respect to the pillars we change the shape of the PC holes and thereby modulate the PC reflectivity. Our measurements show a reflectivity change of more than 80% for a 115-nm lateral displacement.