Showing papers in "Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems in 2015"

Research development of silicon MEMS gyroscopes: a review

Abstract: Micro-electromechenical Systems (MEMS) gyroscope is widely used in many occasions to measure the angular speed of the moving objects and attracts the attentions of many research institutions all over the world This kind of sensor possesses the advantages of high degree of integration, low cost and consumption of power This paper first introduces the research development of silicon MEMS gyroscope since eighties of last century; the researches of many institutions such as Draper Laboratory and UC Berkeley are mentioned and different design principles, control methods and structures are presented This review then presents the key theories and technologies of the sensor and some research results of them In additional, some recent new applications of MEMS gyroscope are also been introduced in this paper such as wearable motion capture system and micro inertial measurement unit Finally, according to the review, some views of silicon MEMS gyroscope and its future prospects are put forwarded

Modeling and analysis of hybrid piezoelectric and electromagnetic energy harvesting from random vibrations

Abstract: We illustrate electroelastic modeling, analysis and simulation solutions, and experimental validation of hybrid piezoelectric (PE) and electromagnetic (EM) energy harvesting from broadband random vibration. For a more practically available ambient source, the more compact expressions of mean power and spectral density (SD) involving dimensionless parameters are derived when the harvester is subjected to random excitation. In the study, it is assumed that the base excitation is white noise. Then, the effect of acceleration SD, load resistance, coupling strength on harvester performances are analyzed by numerical calculation and simulation, and the results are validated by the experimental measurements. It is founded that, only if the load resistance of PE and EM element meet the impedance matching can the hybrid energy harvester output the maximal mean power and spectral density at the resonant frequency, which increases with PE load resistance increasing, but hardly affected by load resistance of EM element; the variation extent of mean power with SD of acceleration increasing varies with the load resistance, and it is up to the maximum under the condition of optimal load; moreover, the stronger the coupling strength is, the wider the frequency band becomes, and the greater the mean power and power spectral density are, while the increasing extent decreases with the coupling strength increasing. Besides, the coupling strength can affect the internal resistance of harvester. Furthermore, with coupling strength increasing, the decreasing degree of mean power falls when the load resistance is greater than the optimal load.

A novel piezo-driven microgripper with a large jaw displacement

Abstract: This paper presents a novel piezo-driven microgripper for micromanipulation. A two-grade amplification mechanism is introduced to enlarge the jaw displacement of the microgripper driven by a piezoelectric actuator (PEA). The design adopts a hybrid flexure structure that integrates flexure hinge and flexure beam to combine their advantages to further improve the microgripper performance. The mechanical designs of two microgrippers with different output manners are first described, one of which is selected to conduct the detailed modeling and analysis. Subsequently, the finite element analysis (FEA) is performed to verify the microgripper performance and the effectiveness of the established models for the investigation of optimum structure parameters. Finally, after the prototype is fabricated, the experimental results show that the developed microgripper possesses the high-precision grasping capacity for different shaped and sized microobjects. Moreover, a large jaw displacement of 150.8 μm corresponding to the 100 V drive voltage and a high amplification ratio of 16.4 can be obtained.

Nonlocal and strain gradient based model for electrostatically actuated silicon nano-beams

Abstract: Conventional continuum theory does not account for contributions from length scale effects which are important in modeling of nano-beams. Failure to include size-dependent contributions can lead to underestimates of deflection, stresses, and pull-in voltage of electrostatic actuated micro and nano-beams. This research aims to use nonlocal and strain gradient elasticity theories to study the static behavior of electrically actuated micro- and nano-beams. To solve the boundary value nonlinear differential equations, analogue equation and Gauss---Seidel iteration methods are used. Both clamped-free and clamped---clamped micro- and nano-beams under electrostatical actuation are considered where mid-plane stretching, axial residual stress and fringing field effect are taken into account for clamped---clamped cases. The accuracy of solution is evaluated by comparison of the pull-in voltages of different micro-electro-mechanical systems with those results previously published in the literature. A main drawback of the previous theoretical researches using nonlocal or strain gradient methods was that they don't account for effects of the size on the Young modulus of the beam and merely they adjust the length scale parameters for small sizes to fit data with experimental results. In the present study, the experimental voltages for static pull-in of different micro- and nano-beams are used to estimate the silicon Young's modulus, nonlocal and length scale parameters. Using the estimated parameters, pull-in voltages of silicon micro- and nano-beams based on strain gradient and nonlocal theories are compared with respect to each other and also with the experimental and previous theoretical results. The conducted results demonstrate that the predicted pull-in voltages using proposed strain gradient theory will give the best fit with experimental observations.

Design and investigation of a low insertion loss, broadband, enhanced self and hold down power RF-MEMS switch

Abstract: This paper presents a low insertion loss capacitive shunt RF-MEMS switch. In the presented design, float metal concept is utilized to reduce the capacitance in up-state of the device. Float metal switch shows an insertion loss <0.11 dB, a return loss below 26.27 dB up to 25 GHz as compared to 0.81 dB insertion, 8.67 dB return loss for the conventional switch without float metal. OFF state response is same for the both devices. Further pull-in voltage of 12.75 V and switching time of 69.62 µs have been observed in case of the conventional switch whereas device with float metal have 11.75 V and 56.41 µs. Improvement of around 2.5 times in bandwidth and 4 times in input power has been observed without self actuation, hold down problem. The designed switch can be useful at device and sub-system level for multi-band applications.

Piezoelectric energy harvester using mechanical frequency up conversion for operation at low-level accelerations and low-frequency vibration

Abstract: In this paper, we propose a modified frequency up-conversion mechanism to lower the operational acceleration level for energy harvesting devices using a snap-through buckling phenomenon. The proposed device consists of a buckled bridge beam clamped on flexible sidewalls with a proof mass and cantilever beams attached to the bridge. When subject to a vibration, the buckled bridge beam snaps through between two stable states, inducing impulsive acceleration on the attached piezoelectric cantilevers. During the snap-through transition, the flexible sidewalls deflect outward, thus lowering the threshold acceleration value for the state transition. Various sidewall materials with different flexibilities were tested to determine the maximum output power, bandwidth, and output characteristics for various input acceleration values. The minimum acceleration value for snap-through transition was 0.5g (g = 9.8 m/s2) when using latex sidewalls. A maximum output power of 0.4 mW Hz/cm2--that is 10 μW for test sample at an excitation frequency of 15 Hz--was generated by using the proposed device with latex sidewalls.

Development of high temperature resistant of 500 °C employing silicon carbide (3C-SiC) based MEMS pressure sensor

Abstract: This works reports a packaged MEMS capacitive pressure sensor (CPS) employing single crystal 3C-SiC thin film as a diaphragm. The details of the design and fabrication steps involved bulk micromachining process. The 3C-SiC-on-Si wafer is back-etched the bulk Si to leave 3C-SC thin film by applied ProTEK PSB coating as a newly photosensitive layer. The ProTEK PSB is exposed into desired pattern of MEMS capacitive pressure sensor and the exposed pattern is developed by developer (ethylene lactate). The photosensitive can be stripped off with strong combination acid such as 2-(1-methoxy)propyl acetate, ethyl acetoacetate and photoacid generator which is attack the exposed ProTEK PSB while unexposed ProTEK PSB areas remain contact the alignment on the wafer surfaces. The prototypes of a MEMS capacitive pressure is packaged for high temperature up to 500 °C and characterized under static pressure of 5.0 MPa in a stainless steel chamber with direct capacitance measurement using LCR meter. The diaphragm of 3C-SiC thin film has the thicknesses of 1.0 µm and the size of 2.0 × 2.0 mm. At room temperature (27 °C), the sensitivity of the sensor is 0.00962 pF/MPa in the range of (1.0---5.0 MPa), with nonlinearity of 0.49 %. At 300 °C, the sensitivity is 0.0127 pF/MPa, and nonlinearity of 0.46 %. The sensitivity increased by 0.0031 pF/MPa, corresponding temperature coefficient of sensitivity is 0.058 %/ °C. At 500 °C, the maximum temperature coefficient of output change is 0.073 %/ °C being red at 5.0 MPa. The main impact of this work is the ability of the sensor to operate up to 500 °C, compare to the previous work using similar 3C-SiC diaphragm that can operates only 400 °C. The main impact of this work is the ability our CPS to operate up to 500 °C and pressure of 5 MPa to surpass the performance of previous work at lower temperature and pressure. In addition, this CPS has reliable stainless steel (SS) o-ring packaging with a direct assembly approach to reduce manufacturing cost and easy installation and maintenance environment.

Polysilicon thin film piezoresistive pressure microsensor: design, fabrication and characterization

Abstract: Polysilicon based pressure sensors use a silicon dioxide layer for isolation of piezoresistors from bulk. This helps in reducing the leakage current compared to the p---n junction isolation in silicon piezoresistors. They are also more cost effective than silicon-on-insulator (SOI) based sensors for high temperature applications. This paper reports the design, fabrication process and characterization of a polysilicon piezoresistive pressure sensor with wet bulk micromachined diaphragm. Novel meander shaped polysilicon piezoresistors are placed at optimized locations, found using finite element method (FEM) simulations, to experience high stress. The effect of clamping conditions of the diaphragm on the piezoresistors placement is shown through FEM simulations and the piezoresistor shapes are designed to keep the metal lines outside the diaphragm structure for better reliability. After fabrication and dicing, the mechanical characterization of the sensor is performed using laser doppler vibrometer (LDV) for determining the first mode resonance frequency and transient response of the sensor diaphragm. A first mode resonant frequency of 306.6 kHz and a response time of 0.56 ms are obtained. The sensor is then packaged inside a customized jig and tested with pressure load for determining the static and temperature characteristics of the sensor in the pressure range of 0---30 Bar. The sensor is tested at three different temperatures, viz. ?5, 25 and 55 °C. A sensitivity of 3.35---3.73 mV/Bar, non-linearity of less than 0.3 %, and a hysteresis of less than 0.1 % are obtained for all the test temperatures.

Design, modeling, and characterization of a MEMS electrothermal microgripper

Abstract: In this paper, a MEMS electrothermal microgripper is introduced, analyzed and tested. The microgripper has been fabricated using the PolyMUMPs surface micromachining process. Analytical models were established based on the electro-thermal and thermo-mechanical analysis to describe the mechanical performances of the microgripper. Axial deformations including first-order nonlinear strain---displacement relations are also included to account for the presence of thermal loading. The materials parameters that significantly affect the performance of the microgripper are discussed, including the thermal conduction, convective and temperature-dependent resistivity. The experimental results show that input voltages below 14 V are required for the microgripper to achieve the jaws deflection in 9.1 μm. Both the experimental and analytical results are in good agreement with the results of modeling. To demonstrate the reliability of the microgripper, the repeatability and reproducibility of jaws gap were tested.

Recent progress in low temperature nanoimprint lithography

Abstract: Nanoimprint lithography is a low cost and high throughput technology to fabricate nanostructures with excellent resolution. However, traditional thermal nanoimprint limits its application field because high temperature induces many problems. Low temperature nanoimprint lithography, including ultraviolet nanoimprint lithography and room temperature nanoimprint lithography, can reduce or remove thermal cycle, overcome the sticking problem, alleviate the alignment errors due to different coefficients of thermal expansion and pattern polymer based materials that are intolerant to high temperature. Recent development of these three low temperature NIL techniques was discussed from the aspects of new resist, stamp, process and application. Low temperature nanoimprint has wide application in the fields of optoelectronics, displays and bio-applications.

Nonlocal thermoelastic nanobeam subjected to a sinusoidal pulse heating and temperature-dependent physical properties

Abstract: This article studies the vibration phenomenon of a nanobeam subjected to a sinusoidal pulse varying heat using the nonlocal Bernoulli---Euler beam theory. A unified generalized thermoelasticity model with one thermal relaxation is used to solve this problem. Both the thermal conductivity and Young's modulus of elasticity are considered linear functions of temperature. An analytical solution in the Laplace domain is obtained for the vibration deflection and temperature. The effect due to the nonlocal parameter and the pulse-width of the sinusoidal pulse varying heat on the lateral vibration, the temperature, the axial displacement and the flexure moment of the nanobeam, is discussed. The results are also obtained in the case of temperature-independent mechanical and thermal properties.

Design of a large displacement thermal actuator with a cascaded V-beam amplification for MEMS safety-and-arming devices

Abstract: The design, fabrication and characterization of a large displacement thermal actuator with a cascaded V-beam amplification for MEMS safety-and-arming (SA) devices are presented. The device is comprised of two V-shape electrothermal actuators, a cascaded V-beam amplification and two mechanical sliders. Compared with conventional lever amplifications, the vertical anti-acceleration stiffness of V-beam amplifications is much larger, which can meet the need of high-acceleration weapons. The special design of two symmetric mechanical sliders can double the displacement to ensure the MEMS SA device in armed state. The whole device is fabricated on a SOI wafer and fabrication process is introduced. Under an applied voltage of 15 V, the displacement of the device is 231.78 μm with consuming power of 5.10 W and response time of 16 ms. The chip size of the actuator is about 4 mm × 5 mm × 0.5 mm. The proposed actuator possesses outstanding performance in miniaturization, low cost and easy integration with other parts of MEMS SA devices.

Realization of a micro pressure sensor with high sensitivity and overload by introducing beams and Islands

Abstract: Presented is a piezoresistive absolute micro pressure sensor for altimetry. This investigation involves the design, fabrication and testing of the sensor. By analyzing the stress distribution of sensitive elements using finite element method (FEM), an improved structure is built up through introducing multi islands and sensitive beams into traditional flat diaphragm. The proposed configuration presents its advantages in terms of enhanced sensitivity and overload resistance compared with the bossed diaphragm and flat diaphragm structures. Multivariate fittings based on ANSYS® simulation results are performed to establish equations about surface stress and deflection of the sensor. Optimization by MATLAB® is carried out to determine the structure dimensions. Silicon bulk micromachining technology is utilized to fabricate the sensor prototype, and the fabrication process is discussed. The output signals under both static and dynamic conditions are evaluated and tested. Experimental results demonstrate the sensor features a relatively high sensitivity of 17.795 μV/V/Pa in the operating range of 500 Pa at room temperature and a proper overload resistance of 200 times overpressure to promise its survival under atmosphere. The favorable performances enable the sensor's application in measuring absolute micro pressure.

Design and simulation of a novel electro-thermally actuated lateral RF MEMS latching switch for low power applications

Abstract: A new lateral electro-thermally actuated latching RF MEMS switch is presented in this paper. In contrast to conventional electrostatic or electro-thermal MEMS switches which require an actuation voltage to hold the switch in on or off state, this switch has a true mechanical latching design in such a way that there is no power required to hold the switch on or off. The switch structure only consumes power while transition between states. In order to satisfy low voltage operation, electro-thermal actuators are chose as the drive and latching actuators of the switch. The required actuation voltage for drive and latching actuators is 6 V. The switch consumes a power of <99 mW while transition from off to on state and also consumes a power of 46 mW for 0.3 ms in transition from off to on states. FEM simulations show that the return loss of the switch is below ?10 dB up to 140 GHz and is below ?20 dB up to 40 GHz. The insertion loss of the switch is less than ?1 dB up to 150 GHz. The switch isolation when it is off is below ?20 dB up to 160 GHz. The switch has potential applications in low voltage, low power and high performance RF tuning and switching applications.

Interference characteristics in a Fabry---Perot cavity with graphene membrane for optical fiber pressure sensors

Abstract: Due to higher mechanical strength and ultra-thin thickness, graphene is used as a sensitive diaphragm in a Fabry---Perot cavity to improve the sensitivity of pressure sensors. In accordance with the working principle of Fabry---Perot interferometer, a load---deflection mathematical model of fiber-tip pressure sensor with graphene membrane is established based on the large deflection elastic theory of circular membrane. The effects of membrane parameters, including prestressing force and membrane layer number, on deflection mechanical behaviors are studied by using finite element method. Also, the effects of graphene membrane layer and incident light angle on the film reflectivity are obtained according to the refractive index characteristics of the membrane. The simulation results show that an approximate linear relation between loads and deflections exists in the simulated pressure range from 0 to 3.5 kPa, and a theoretical pressure sensitivity of 1,096 nm/kPa for a single-layered graphene membrane can be achieved. To estimate the performance of multi-layered graphene membrane as the diaphragm, an extremely thin 13-layered 125-μm diameter graphene diaphragm is fabricated on the tip of the fiber end, which forms a low finesse Fabry---Perot interferometer. The Fabry---Perot cavity with a length of 40 μm can exhibit a fringe visibility of approximate 0.56 with a measured membrane reflectivity of 1.49 %. The experimental results demonstrate that the use of graphene as diaphragm material would allow highly sensitive and miniature fiber-tip sensors.

The fabrication of back etching 3C-SiC-on-Si diaphragm employing KOH + IPA in MEMS capacitive pressure sensor

Abstract: The 680 µm thick wafer is back-etched, leaving the thin film 3C-SiC as the flexible diaphragm to detect pressure. The etching processes are performed with three different KOH concentrations (35, 45 and 55 %), without and with 10 % IPA surfactant and the etching temperatures of 50 and 80 °C. Graphs are plotted on the effect of the etch rate and etch depth against these three parameters. In addition, the surface roughnesses of the diaphragms at these conditions are measured, photographed and analyzed. The results show that the back-etching of a 3C-SiC-on-Si wafer is fastest at higher temperature and KOH concentration and without IPA surfactant, but at the price of higher surface roughness. The addition of 10 % IPA reduces the surface roughness significantly. We also notice the increasing presence of micro-pipes at higher KOH concentration and etching temperature. The experiments are performed using bulge test method that induces the effects of dimensional layout diaphragm of 2,000 and 2,500 µm, the curve shows a good resemblance each other at pressure of 5.0 MPa. The maximum difference linearity of 2,000 and 2,500 µm is 98.7 and 97.1 %, respectively. It is revealed that the small layout dimensional can sustain the diaphragm at high pressure compare with large dimensional layout of 3,000 and 3,500 µm with the linearity is about 73.2 and 62.6 %, respectively.

RF-MEMS: an enabling technology for modern wireless systems bearing a market potential still not fully displayed

Abstract: Since its first discussions in literature during late `90 s, RF-MEMS technology (i.e. Radio Frequency MicroElectroMechanical-Systems) has been showing uncommon potential in the realisation of high performance and widely reconfigurable RF passives for radio and telecommunication systems. Nonetheless, against the most confident forecasts for successful exploitation of RF-MEMS technology in mass-market applications, with the mobile phone segment first in line, already commencing from the earliest years of the 2000s, first design wins for MEMS-based RF passives have started to be announced just recently. This paper tries to depict and interpret the substantial circumstances that made RF-MEMS technology fail repeatedly, for about one decade, market forecasts. With the graphical support of the hype cycle concept, it will be shown that missed success of RF-MEMS was first caused by intrinsic (i.e. technology-related) factors. Subsequently, extrinsic elements linked to market acceptance and needs of such a technology, not fully weighted since the beginning, caused the second wave of disappointment around RF-MEMS. Quite unexpectedly, the context has changed rather significantly in recent years. The smartphones market segment started to generate a factual need for highly reconfigurable and high performance RF passive networks, and this circumstance is increasing the momentum of RF-MEMS technology that was expected about one decade ago. This work frames the current state of RF-MEMS market exploitation, also providing highlights on further expansion in mobile and telecommunication systems. Eventually, a focused state of the art report is developed around recent RF-MEMS research findings driven by requirements imposed by current market applications.

Design, fabrication and characterization of high performance SOI MEMS piezoresistive accelerometers

Abstract: Piezoresistive accelerometers have served as the frontrunners in micromachined accelerometer technology and have undergone modifications with the primary focus on device complexity and novel processes to circumvent performance trade-offs. This work comprises the analysis, design and development of micromachined SOI MEMS-based piezoresistive accelerometers for inertial sensing applications using minimalistic component design and a custom fabrication process to realize robust devices capable of withstanding more than ~106 cycles of error-free operation. Extensive simulation studies have been carried out to validate and tune the design parameters of the analytical models used. The devices have been subjected to an exhaustive range of static and dynamic tests to characterize their response which has been sensitive and highly linear with low noise, an intrinsic quality of piezoresistive sensors coupled with precision design and fabrication.

Parallel integration of ionic wind generators on PCBs for enhancing flow rate

Abstract: We report a novel ionic wind generator in which many single ionic wind generators are tightly integrated in parallel on printed circuit boards (PCBs). Experimental measurements demonstrate that the device produces an enhanced volumetric air flow by virtue of a large cross-sectional area. Although the parallel connection of multiple generators causes interference between parallel air jets, which degrades the wind speed, we reduce the interference with a shielding layer between the corona and collector electrodes. The proposed design for integrating multiple ionic wind generators on PCBs offers the potential for applications in cooling small electrical devices with the intrinsic characteristics of ionic wind generators, which are motionlessness, silence, and compactness.

A flexible dry micro-dome electrode for ECG monitoring

Abstract: This paper describes a flexible dry electrode with micro domes on polydimethylsiloxane (PDMS) for the monitoring of electrocardiogram (ECG). The fabrication procedure of this microstructure was mainly composed of melting photoresist, double-PDMS-molding, nickel (Ni) plating and encapsulation between two thin PDMS films. To investigate the performance of the fabricated micro-dome electrode, three dry electrodes with different arrays were fabricated to conduct the contact impendence measurements. ECG signals were measured by both the standard wet electrodes (Ag/AgCl) and dry electrodes. Experimental results showed the dry electrode provided signal quality that was comparable to the standard wet electrode without the need for skin preparation or electrolytic solution. The proposed dry electrode is more comfortable, with less skin irritation and requires no conductive gel. Thus, this flexible dry micro-dome electrode could find potential biomedical applications in health monitoring.

A new silicon biaxial decoupled resonant micro-accelerometer

Abstract: In this paper, the design, the simulation, the fabrication and the experiment of a new silicon biaxial decoupled resonant micro-accelerometer are presented The new biaxial resonant micro-accelerometer consisting of four identical tuning forking resonators, four pairs of decoupled beams, four lever mechanisms and a proof mass is decoupled by four pairs of decoupling beams in two sensitive directions, which will benefit to isolate the acceleration detections of the two axes The simulation results prove that the proposed structure is able to decouple the planar 2-D acceleration into two independent acceleration components And the two pairs of the decoupled resonator modes which are 23893, 23946 and 26974, 26999 kHz separately have a 3 kHz difference in frequency in order to suppress the mutual interference Then the fabrication, the vacuum encapsulation and the design of oscillation loop and the frequency measurement circuit are illustrated Experimental results show that the new biaxial decoupled resonant micro-accelerometer has good performance with the transverse sensitivity of 108 % in x-axis and 133 % in y-axis, the bias stability of 0294 mg in x-axis and 0278 mg in y-axis, and dynamic range of over 10 g, which proves that the new biaxial resonant micro-accelerometer is practicable and has an excellent decoupled performance

Improving voltage output with PZT beam array for MEMS-based vibration energy harvester: theory and experiment

Abstract: Piezoelectric vibration energy harvesters as an autonomous power source for various types of sensors, actuators and MEMS devices have attracted increasing attention in recent years. Traditional MEMS-based PZT single beam vibration energy harvester has low voltage output (usually <1 V) which causes rectifier circuit to consume most of power or turn off in practical applications. In this paper, in order to improve the voltage output of MEMS-based PZT vibration energy harvester as well as ensure high power output, a PZT beam array configuration for MEMS-based vibration energy harvester is proposed. Based on Hamilton's principle and Euler---Bernoulli beam theory, mathematical model for the proposed vibration energy harvester is established. Two different dimensions MEMS-based PZT beam array vibration energy harvesters are designed and fabricated through micro-fabrication techniques. The performances of the two types of fabricated vibration energy harvesters are characterized and compared with traditional vibration energy harvester in experiment. Experimental results agree well with theoretical analysis, and the experimental results show that the better performance fabricated vibration energy harvester can generate 121.4 μW and 3.5 V respectively at 1 g acceleration.

Simulation study on performance of MEMS piezoelectric energy harvester with optimized substrate to piezoelectric thickness ratio

Abstract: Piezoelectric energy harvester produces electrical energy based on direct piezoelectric effect. Cantilevered structures with piezoelectric layers are used as MEMS piezoelectric energy harvester for more than one decade. This paper reports on simulation study on performance of MEMS piezoelectric energy harvester with optimized substrate to piezoelectric layer thickness ratio. Stainless steel and single crystal PMN32 are used as substrate and piezoelectric materials respectively. Four different structures are designed and the thickness ratio of substrate to piezoelectric layer is varied to study its effect on performance of MEMS piezoelectric energy harvester. The performance of MEMS piezoelectric energy harvester is simulated using the software COMSOL Multiphysics.

Design of experiments based factorial design and response surface methodology for MEMS optimization

Abstract: This paper presents the application of the design of experiments technique based factorial designs and response surface methodology (RSM) for optimization of MEMS devices. The RSM methodology is used to optimize the geometric parameters of the symmetric toggle RF MEMS switch to minimize the switch pull-in voltage. Fractional factorial based Plackett---Burman screening design is developed and the corresponding pull-in voltage is obtained, through finite element method (FEM) based simulations, for different combinations of the dimensional parameters. Analysis of variance is performed to distinguish the most significant parameters affecting the output response. The significant parameters, obtained using Plackett---Burman screening design, are further investigated using second order Box---Behnken design to obtain the optimal levels of the significant parameters and analyze their interactions. Regression analysis is carried out to check the adequacy of the Box---Behnkan based response surface model for predicting the output response. The effect of the significant parameters and their interactions on the pull-in voltage is analyzed through model based 3D surface and contour plots. The optimal levels of the parameters for a pull-in voltage $$\le$$ ≤ 15 V, with compact device dimensions, are determined and verified through FEM simulations. A comparison is made for the results obtained through RSM with the analytical results presented in the literature. This showed a close agreement, verifying the practicability of this approach for the optimization of MEMS devices.

Modeling the size dependent instability of NEMS sensor/actuator made of nano-wire with circular cross-section

Abstract: It is well established that electromechanical response of a nano-electromechanical system (NEMS) might be size-dependent. Herein, the size dependent electrostatic instability of NEMS sensor/actuator fabricated from nano-wires with circular cross-section is theoretically investigated considering the effects of the Coulomb electrostatic and van der Waals molecular attractions. For this purpose, modified couple stress theory is applied to model the size effect on the instability of the system. The van der Waals and Coulomb attractions are computed from the simplified Lennard---Jones potential and the electrical capacitance model, respectively. In order to solve the nonlinear constitutive equation of the system, four different approaches including modified variational iteration method, monotonic iteration method, lumped parameter model and numerical solution are employed. It is found that when the diameter of the nano-wire is comparable with the intrinsic material length scale, size effect can substantially influence the pull-in voltage of the system. Interestingly, a coupling between van der Waals force and size dependency can affect the instability deflection of the sensor/actuator.

A complete analytical model for circular diaphragm pressure sensor with freely supported edge

Abstract: Microelectromechanical systems (MEMS) pressure sensors have been designed and characterized. Initially deflection, stress and strain of the pressure sensor are computed based on mechanics of diaphragm structure for circular shape in accordance with the theory of elasticity. The results have been simulated to define and understand the importance of various impact parameters such as sensitivity, optimization of resistor length etc. Moreover the present work also demonstrates the design of MEMS pressure sensor using solidworks. It allows detailed visualization of the parameters computed and supports the theory undertaken.

Graphene diaphragm analysis for pressure or acoustic sensor applications

Abstract: Graphene has remarkable mechanical properties, and it is a very promising material for sensors. The progress of graphene diaphragm based pressure sensor was detailed firstly. Then the deflection of pressurized circular graphene diaphragm with pre-stress was discussed, an approximate solution was given to substitute Hencky's series solution. Pre-stress descends the sensitivity of the graphene diaphragm, but it also makes the deflection linear in pre-stress dominated regime, which is important for sensor applications. The pre-stress in the diaphragm caused by van der Waals force between the diaphragm and the sidewall of the substrate was studied, the results indicates that the pre-stress is associated with the adhesion energy per unit area between the diaphragm and sidewall of the substrates, and the thickness of the diaphragm. Due to the influence of the the adhesion force, multilayer (2~10 layers) graphene diaphragms are more sensitive than monolayer, as monolayer graphene is much more flexible, the adhesion energy is higher than multilayer graphene.

Novel polyvinyl alcohol/silver hybrid nanocomposites for high performance electromagnetic wave shielding effectiveness

Abstract: A novel conducting polyvinyl alcohol (PVA) reinforced silver (Ag) nanoparticles were successfully synthesized for electromagnetic wave shielding at microwave frequency. The microstructures of the nanocomposites were examined by means of X-ray diffraction, field-emission scanning electron microscope and transmission scanning microscopy. Mechanical and electrical properties of PVA/Ag nanocomposite were investigated in detail. With the inclusion of 10 wt% Ag nanoparticles to PVA matrix, an electromagnetic interference shielding effectiveness of magnitude in the range of 51 dB in the microwave frequency was obtained. The prepared new nanocomposites can be used in the microwave devices and also for biomedical applications with low cost.

Design of compact and wide bandwidth SPDT with anti-stiction torsional RF MEMS series capacitive switch

Abstract: This paper presents a new single pole double throw (SPDT) RF MEMS switch design based on a torsional series capacitive switch. The torsional configuration and use of floating metal reduce the stiction probabilities. Use of a single series capacitive switch compared to the conventional approach of a capacitive and series combination, offers compact size, higher bandwidth and superior reliability. The optimized SPDT topology offers a wider bandwidth of 17 GHz (3---20 GHz) with insertion loss of ?0.3 to ?0.4 dB and isolation ?20 to ?44 dB. The proposed structure actuates at 9 V and the contact force varies in the elastic contact regime from 20 to 68 µN for the bias voltage of 10---15 V.

Plasma separation and preparation on centrifugal microfluidic disk for blood assays

Abstract: The present study proposes a simple lab-on-CD device in which the plasma is first separated from the whole human blood, then divided into two samples of equal volume, and finally decanted into a detection chamber for analysis purposes. The performance of the proposed device is then evaluated using blood samples with hematrocrit concentrations ranging from 6 to 48 %. The results show that for a blood sample with a hematocrit concentration of 6 %, a separation efficiency of 96 % can be achieved within 5---6 s. Moreover, the two plasma samples collected from the left and right branches of the optimized Y-shaped splitter network differ in volume by no more than 0.5 nL. It is shown that the volume of plasma decanted into the detection chamber can be precisely controlled through an appropriate manipulation of the disk rotation speed. Finally, the practical feasibility of the proposed device is demonstrated by performing a creatinine test, the linear dynamic range show that it can be used for creatinine detection in blood assay. In this study, systematical evaluation on the functionality and performance of such a device has been done. The merits of this device are its low cost, straightforward fabrication process, low sample consumption, and high portability.