An efficient numerical approach to electrostatic microelectromechanical system simulation

Computational analysis of electrostatic microelectromechanical systems （MEMS） requires an electrostatic analysis to compute the electrostatic forces acting on micromechanical structures and a mechanical analysis to compute the deformation of micromechanical structures. Typically, the mechanical analysis is performed on an undeformed geometry. However, the electrostatic analysis is performed on the deformed position of microstructures. In this paper, a new efficient approach to self-consistent analysis of electrostatic MEMS in the small deformation case is presented. In this approach, when the microstructures undergo small deformations, the surface charge densities on the deformed geometry can be computed without updating the geometry of the microstructures. This algorithm is based on the linear mode shapes of a microstructure as basis functions. A boundary integral equation for the electrostatic problem is expanded into a Taylor series around the undeformed configuration, and a new coupled-field equation is presented. This approach is validated by comparing its results with the results available in the literature and ANSYS solutions, and shows attractive features comparable to ANSYS.

Low-Power Operational Amplifier for Real-Time Signal Processing System of Micro Air Vehicle

A low-power complementary metal oxide semiconductor（CMOS） operational amplifier （op-amp） for real-time signal processing of micro air vehicle （MAV） is designed in this paper.Traditional folded cascode architecture with positive channel metal oxide semiconductor（PMOS） differential input transistors and sub-threshold technology are applied under the low supply voltage.Simulation results show that this amplifier has significantly low power,while maintaining almost the same gain,bandwidth and other key performances.The power required is only 0.12 mW,which is applicable to low-power and low-voltage real-time signal acquisition and processing system.

Twisting Sliding Mode Control of an Electrostatic MEMS Micromirror for a Laser Scanning System

In this paper,we present a twisting control scheme with proportional-integral-derivative(PID)sliding surface for a two-axis electrostatic torsional micromirror,and the utilization of the proposed scheme in a laser scanning system.The experimental results of set-point regulation verify that the proposed scheme provides enhanced transient response and positioning performance as compared to traditional sliding mode control.To evaluate the tracking performance of the closed-loop system,triangular waves with different frequencies are used as desired traces.With the proposed scheme the experimental results verified that the closed-loop controlled micromirror follows the given triangular trajectories precisely.A micromirror-based laser scanning system is developed to obtain images.When compared with open-loop control,the experimental results demonstrated that the proposed scheme is able to reduce the distortion of the raster scan,and improve the imaging performance in the presence of cross-coupling effect.

Numerical Simulation of Shock Resistant Microsystems (MEMS)

The mechanical response of shock-loaded microelectromechanical systems (MEMS) is simulated to formulate guidelines for the design of dynamically reliable MEMS. MEMS are modeled as microstructures supported on elastic substrates, and the shock loads are represented as pulses of acceleration applied by the package on the substrate over a finite time duration. For typical MEMS and shock loads, the response of the substrate is closely approximated by rigid-body motion. Results indicate that modeling the shock force as a quasi-static force for MEMS with low-natural frequencies may lead to erroneous results. A criterion is obtained to distinguish between the dynamic and quasi-static responses of the MEMS.

Electrode design for multimode suppression of aluminum nitride tuning fork resonators

This paper is focused on electrode design for piezoelectric tuning fork resonators.The relationship between the performance and electrode pattern of aluminum nitride piezoelectric tuning fork resonators vibrating in the in-plane flexural mode is investigated based on a set of resonators with different electrode lengths,widths,and ratios.Experimental and simulation results show that the electrode design impacts greatly the multimode effect induced from torsional modes but has little influence on other loss mechanisms.Optimizing the electrode design suppresses the torsional mode successfully,thereby increasing the ratio of impedance at parallel and series resonant frequencies(R_(p)/R_(s))by more than 80%and achieving a quality factor(Q)of 7753,an effective electromechanical coupling coefficient(kt_(eff)^(2))of 0.066%,and an impedance at series resonant frequency(R_(m))of 23.6 kΩ.The proposed approach shows great potential for high-performance piezoelectric resonators,which are likely to be fundamental building blocks for sensors with high sensitivity and low noise and power consumption.

A novel multifunctional electronic calibration kit integrated by MEMS SPDT switches

Design and simulation results of a novel multifunctional electronic calibration kit based on microelectromechanical system(MEMS)single-pole double-throw(SPDT)switches are presented in this paper.The short-open-load-through(SOLT)calibration states can be completed simultaneously by using the MEMS electronic calibration,and the electronic calibrator can be reused 10^(6) times.The simulation results show that this novel electronic calibration can be used in a frequency range of 0.1 GHz–20 GHz,the return loss is less than 0.18 dB and 0.035 dB in short-circuit and open-circuit states,respectively,and the insertion loss in through(thru)state is less than 0.27 dB.On the other hand,the size of this novel calibration kit is only 6 mm×2.8 mm×0.8 mm.Our results demonstrate that the calibrator with integrated radiofrequency microelectromechanical system(RF MEMS)switches can not only provide reduced size,loss,and calibration cost compared with traditional calibration kit but also improves the calibration accuracy and efficiency.It has great potential applications in millimeter-wave measurement and testing technologies,such as device testing,vector network analyzers,and RF probe stations.

Effects of Material and Dimension on TCF,Frequency,and Q of Radial Contour Mode AlN-on-Si MEMS Resonators

This paper investigates the effects of material and dimension parameters on the frequency splitting,frequency drift,and quality factor(Q)of aluminium nitride(AlN)-on-n-doped/pure silicon(Si)microelectromechanical systems(MEMS)disk resonators through analysis and simulation.These parameters include the crystallographic orientation,dopant,substrate thickness,and temperature.The resonators operate in the elliptical,higher order,and flexural modes.The simulation results show that i)the turnover points of the resonators exist at 55°C,-50°C,40°C,and-10°C for n-doped silicon with the doping concentration of 2×1019 cm-3 and the Si thickness of 3.5μm,and these points are shifted with the substrate thickness and mode variations;ii)compared with pure Si,the modal-frequency splitting for n-doped Si is higher and increases from 5%to 10%for all studied modes;iii)Q of the resonators depends on the temperature and dopant.Therefore,the turnover,modal-frequency splitting,and Q of the resonators depend on the thickness and material of the substrate and the temperature.This work offers an analysis and design platform for high-performance MEMS gyroscopes as well as oscillators in terms of the temperature compensation by n-doped Si.

A novel low-loss four-bit bandpass filter using RF MEMS switches

This paper details the design and simulation of a novel low-loss four-bit reconfigurable bandpass filter that integrates microelectromechanical system(MEMS)switches and comb resonators.A T-shaped reconfigurable resonator is reconfigured in a'one resonator,multiple MEMS switches'configuration and used to gate the load capacitances of comb resonators so that a multiple-frequency filtering function is realized within the 7-16 GHz frequency range.In addition,the insertion loss of the filter is less than 1.99 dB,the out-of-band rejection is more than 18.30 dB,and the group delay is less than 0.25 ns.On the other hand,the size of this novel filter is only 4.4 mm×2.5 mm×0.4 mm.Our results indicate that this MEMS reconfigurable filter,which can switch 16 central frequency bands through eight switches,achieves a low insertion loss compared to those of traditional MEMS filters.In addition,the advantages of small size are obtained while achieving high integration.

Lumped parameter analytic modeling and behavioral simulation of a 3-DOF MEMS gyro-accelerometer

A new analytical model of a 3-degree-of-freedom （3-DOF） gyro-accelerometer system consisting of a 1-DOF drive and 2-DOF sense modes is presented. The model constructs lumped differential equations associated with each DOFof the system by vector analysis. The coupled differential equations thus established are solved analytically for their responses in both the time and frequency domains. Considering these frequency response equations, novel device design concepts are derived by forcing the sense phase to zero, which leads to a certain relationship between the structural frequencies, thereby causing minimization of the damping effect on the performance of the system. Furthermore, the feasibility of the present gyro-accelerometer structure is studied using a unique discriminatory scheme for the detection of both gyro action and linear acceleration at their events. This scheme combines the formulated settled transient solution of the gyro-accelerometer with the processes of synchronous demodulation and filtration, which leads to the in-phase and quadrature components of the system＇s output signal. These two components can be utilized in the detection of angular motion and linear acceleration. The obtained analytical results are validated by simulation in a MATLAB/Simulink environment, and it is found that the results are in excellent agreement with each other.

SIMPLIFIED SCALING TRANSFORMATION FOR THE NUMERICAL SIMULATION OF MEMS DEVICES WITH THIN FILM STRUCTURES

Thin film is a widely used structure in the present microelectromechanical systems （MEMS） and plays a vital role in many functional devices. However, the great size difference between the film＇s thickness and its planar dimensions makes it difficult to study the thin film performance numerically. In this work, a scaling transformation was presented to make the different dimensional sizes equivalent, and thereby, to improve the grid quality considerably. Two numerical experiments were studied to validate the present scaling transformation method. The numerical results indicated that the largest grid size difference can be decreased to one to two orders of magnitude by using the present scaling transformation, and the memory required by the numerical simulation, i.e., the total grid number, could be reduced by about two to three orders of magnitude, while the numerical accuracies with and without this scaling transformation were nearly the same.

A MEMS Based Amperometric Immunosensor with Self-assembled Monolayers Immobilization Technique

Based on MEMS technology,immunosensor with an'Au,Pt,Pt'three-microelectrode system enclosed in a SU-8 micro pool was fabricated.Employing SAMs technique,the Au electrode was modified by cysteamine(Cys)to assemble gold nanopanicles(nanogold)layer,subsequently,a layer of protein G(PG)was immobilized on nanogold layer to further capture antibody orientedly.Compared with the immunosensors using bulky gold electrode and direct PG binding to electrode immobilization technique for antibody,it has attractive advantages,such as miniaturization,good compatibility,broad linear range for human immunoglobulin(HIgG)and easy to be designed into array.

Residual Strains in a Nanometer Thick Cr Film Measured on Micromachined Beams

A Cr film with a 75 nm thickness sputtered on a Si substrate was used to fabricate microbridge and microcantilever samples with the MEMS （microelectromechanical system） technique. The profile of the buckled beams was measured by using the interference technique with white light and fitted with a theoretical result. The uniform residual strain in the bridge samples was deduced from the variation of buckling amplitude with the beam length. On the other hand, the gradient residual strain was determined from the deflection profile of the cantilever. The residual uniform and gradient strain in the Cr film are about 4.96×10^-3 and 4.2967×10^-5, respectively.

A prototype portable instrument employing micro-preconcentrator and FBAR sensor for the detection of chemical warfare agents

The presence of chemical warfare agents(CWAs)in the environment is a serious threat to human safety,but there are many problems with the currently available detection methods for CWAs.For example,gas chromatography–mass spectrometry cannot be used for in-field detection owing to the rather large size of the equipment required,while commercial sensors have the disadvantages of low sensitivity and poor selectivity.Here,we develop a portable gas sensing instrument for CWA detection that consists of a MEMSfabricated micro-preconcentrator(μPC)and a film bulk acoustic resonator(FBAR)gas sensor.The μPC is coated with a nanoporous metal–organic framework material to enrich the target,while the FBAR provides rapid detection without the need for extra carrier gas.Dimethyl methylphosphonate(DMMP),a simulant of the chemical warfare agent sarin,is used to test the performance of the instrument.Experimental results show that the μPC provides effective sample pretreatment,while the FBAR gas sensor has good sensitivity to DMMP vapor.The combination of μPC and FBAR in one instrument gives full play to their respective advantages,reducing the limit of detection of the analyte.Moreover,both the μPC and the FBAR are fabricated using a CMOS-compatible approach,and the prototype instrument is compact in size with high portability and thus has potential for application to in-field detection of CWAs.

Fabrication and Performance of Novel RF Spiral Inductors on Silicon

This paper discusses fabrication and performance of novel circular spiral inductors on silicon. The substrate materials underneath the inductor coil are removed by wet etching process. In the fabrication process, fine polishing of the photoresist is used to simplify the processes and ensure perfect contact between the seed layer and the top of pillars. Dry etching technique is used to remove the seed layer. The results show that Q-factor of the inductor is greatly improved by removing silicon underneath the inductor coil. The spiral inductor with line width of 50 μm has a peak Q-factor of 10 for the inductance of 2.5 nH at frequency of 1 GHz, and the resonance frequency of the inductor is about 8.5 GHz. For the inductor of conductor width 80 μm, the peak Q-factor increases to about 17 for inductance of 1.5 nH in the frequency range of 0.05 -3.00 GHz.

A dynamic macromodel for distributed parameter magnetic microactuators

This paper presents a reduced-order model to describe the mechanical behaviour of microbeam-based magnetic devices. The integration for magnetic force is calculated by dividing the microbeam into several segments, and the nonlinear equation set has been developed based on the magnetic circuit principle. In comparison with previous models, the present macromodel accounts for both the micro-magnetic-core reluctance and the coupling between the beam deflection and magnetic force. This macromodel is validated by comparing with the experimental results available in some papers and finite-element solutions.

Surface Characterisation of Silicon Based MEMS

Polysilicon Microelectromechanical systems(MEMS) are the subject of intensive researches. Surface chemistry and topography of a MEMS test structure fabricated at Sandia National Laboratory, USA, were studied by means of scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS) and atomic force microscopy(AFM). XPS C_ 1sand Si_ 2pspectra from the polysilicon components, silicon nitride substrate and a reference silicon wafer were compared. The results confirm the presence of a self-assembled monolayer(SAM) on the MEMS surface. An island-like morphology was found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 μm in diameter and 20 nm in height. It is concluded that the co-existence of columnar growth and equiaxed growth during the low pressure chemical vapor deposition(LPCVD) of these layers leads to the observed morphology and the islands are caps to the columnar structures.

OPTICAL COHERENCE TOMOGRAPHY FOR BLADDER CANCER DIAGNOSIS:FROM ANIMAL STUDY TO CLINICAL DIAGNOSIS

This paper summarizes the recent technological development in our lab on cystoscopic optical coherence tomography(COCT)by integrating time-domain OCT(TDOCT)and spectral-domain OCT(SDOCT)with advanced MEMS-mirror technology for endoscopic laser scanning imaging.The COCT catheter can be integrated into the instrument channel of a commercial 22Fr rigid cystoscopic sheath for in vivo imaging of human bladder under the cystosocopic visual guidance;the axial/transverse resolutions of the COCT catheter are roughly 9μm and 12μm,respectively,and 2D COCT imaging can be performed with over 110dB dynamic range at 4–8 fps.To examine the utility and potential limitations of OCT for bladder cancer diagnosis,systemic ex vivo rat bladder carcinogenesis studies were performed to follow various morphological changes induced by tumor growth and in vivo porcine study was performed to examine the feasibility of COCT for in vivo imaging.Justified by promising results of the animal studies,preliminary clinical study was conducted on patients scheduled for operating-room cystoscopy for bladder cancers.Double-blind clinical results reveal that COCT can delineate detailed bladder architectures(e.g.,urothelium,lamina propria,muscularis)at high resolution and detect bladder cancers based on enhanced urothelial heterogeneity as a result of excessive growing nature of bladder cancers.The diagnostic sensitivity and specificity can be enhanced to 92%and 85%,respectively.Results also suggest that due to reduced imaging depth of COCT in cancerous lesions,staging of bladder cancers may be limited to Ta or T1 for non-outgrowing cancerous lesions.

Release Method of Microobjects Based on Piezoelectric Vibration

A release method of microobjects is presented based on the piezoelectric vibration.To achieve an effective release,the piezoelectric vibration is added to overcome adhesion force happened in the microoperation.This technique employs inertia force to overcome adhesion force,thereby achieving 90%repeatability with a releasing accuracy of 4± 0.5μm,which was experimentally quantified through the manipulation of 20—80μm polystyrene spheres under an optical microscope.Experimental results confirmed that this adhesion control technique was independent of substrate.Theoretical analyses were conducted to understand the releasing mechanism.Therefore,the micromanipulation system proved to be effective for active releasing of micromanipulation.A novel gripper structure with triple finger is devised.In the design,three cantilevers are considered as the end effectors of the fingers,driven by piezoelectric ceramic transducer(PZT).Tungsten tipped probes are used to pick and place the micro objects.

Micromechanical tunable vertical-cavity surface-emitting lasers

We report the study on a short wavelength-tunable vertical-cavity surface-emitting laser utilizing a monolithically integrated bridge tuning microelectromechanical system. A deformable-bridge top mirror suspended above an active region is utilized. Applied bridge-substrate bias produces an electrostatic force which reduces the spacing of air-gap and tunes the resonant wavelength toward a shorter wavelength （blue-shift）, Good laser characteristics are obtained： such as continuous tuning ranges over 11 nm near 940 nm for 0-9 V tuning bias, the peak output power near 1 mW and the full-width-half-maximum limited to approximately 3.2-6.8 rim. A detailed simulation of the micromechanical and optical characteristics of these devices is performed, and the ratio of bridge displacement to wavelength shift has been found to be 3：1.

Nanotechnology in Diagnosis: A Review

The fast pace of today’s world has presented several challenges in the area of healthcare. Depression, hypertension, diabetes, cancers and several infectious diseases are just some of the common outcomes associated with the high speed stress-filled lifestyle. Early diagnosis has been the goal for prompt arrest and management of these health conditions. This has been a challenge in recent times. However, great scientific advancement with improved potential in medical diagnosis has equally been a giant stride in times like these. Early disease detection even before symptoms’ presentation, improved imaging of internal body structure, as well as ease of diagnostic procedures, have been developed with the help of a new branch of laboratory medicine termed nanodiagnostics. Use of microchips, biosensors, nanorobots, nano identification of single celled structures, and microelectromechanical systems are current techniques being developed for use in nanodiagnostics. This piece of write up takes a panoramic view of available nanotechnological advances in current use for medical diagnosis and projecting into future possibilities and potentials for an improved health care delivery.