http://www.mdpi.com/journal/sensors/special_issues/reliability-issues-mems-engineering/ Dear Colleagues, Micro-electro-mechanical-systems (MEMS) are devices on a millimeter scale, with micro-resolution. Each MEMS is given by the integration of mechanical elements, sensors, actuators and electronics on a common silicon substrate, obtained through micro-fabrication technology. MEMS are often designed to work in mobile devices, and are therefore subject during their life to accidental mechanical loadings. Because of the MEMS size, multi-scale analyses are sometimes required in reliability analysis. Furthermore, also thermal, electrical, magnetic and environmental actions should be accounted for in a fully coupled multi-physics modelling of the devices. As for packaging, some technical problems caused to the devices are not yet thoroughly understood and solved. Since standards do not necessarily apply to packaged MEMS, new knowledge-based testing methodologies need to be proposed. The aim of this special issue is to collect high quality research results on all these aspects of MEMS engineering. Dr. Stefano MarianiGuest Editor{snippet name="submission_info"} http://www.mdpi.com/1424-8220/10/2/1232/ Hydrogen plays a significant role in various industrial applications, but careful handling and continuous monitoring are crucial since it is explosive when mixed with air. Surface Acoustic Wave (SAW) sensors provide desirable characteristics for hydrogen detection due to their small size, low fabrication cost, ease of integration and high sensitivity. In this paper a finite element model of a Surface Acoustic Wave sensor is developed using ANSYS12© and tested for hydrogen detection. The sensor consists of a YZ-lithium niobate substrate with interdigital electrodes (IDT) patterned on the surface. A thin palladium (Pd) film is added on the surface of the sensor due to its high affinity for hydrogen. With increased hydrogen absorption the palladium hydride structure undergoes a phase change due to the formation of the β-phase, which deteriorates the crystal structure. Therefore with increasing hydrogen concentration the stiffness and the density are significantly reduced. The values of the modulus of elasticity and the density at different hydrogen concentrations in palladium are utilized in the finite element model to determine the corresponding SAW sensor response. Results indicate that with increasing the hydrogen concentration the wave velocity decreases and the attenuation of the wave is reduced. http://www.mdpi.com/1424-8220/10/2/1232/ Tue, 02 Feb 2010 00:00:00 CET Sensors 2010-02-02 10 2 Article 1232 1250 1424-8220 A Finite Element Model of a MEMS-based Surface Acoustic Wave Hydrogen Sensor 2010-02-02 doi: 10.3390/s100201232 Mohamed M. EL Gowini Walied A. Moussa http://www.mdpi.com/1424-8220/9/12/9945/ A major problem that often arises in modeling Micro Electro Mechanical Systems (MEMS) such as Surface Acoustic Wave (SAW) sensors using Finite Element Analysis (FEA) is the extensive computational capacity required. In this study a new approach is adopted to significantly reduce the computational capacity needed for analyzing the response of a SAW sensor using the finite element (FE) method. The approach is based on the plane wave solution where the properties of the wave vary in two dimensions and are uniform along the thickness of the device. The plane wave solution therefore allows the thickness of the SAW device model to be minimized; the model is referred to as a Reduced 3D Model (R3D). Various configurations of this novel R3D model are developed and compared with theoretical and experimental frequency data and the results show very good agreement. In addition, two-dimensional (2D) models with similar configurations to the R3D are developed for comparison since the 2D approach is widely adopted in the literature as a computationally inexpensive approach to model SAW sensors using the FE method. Results illustrate that the R3D model is capable of capturing the SAW response more accurately than the 2D model; this is demonstrated by comparison of centre frequency and insertion loss values. These results are very encouraging and indicate that the R3D model is capable of capturing the MEMS-based SAW sensor response without being computationally expensive. http://www.mdpi.com/1424-8220/9/12/9945/ Tue, 08 Dec 2009 00:00:00 CET Sensors 2009-12-08 9 12 Article 9945 9964 1424-8220 A Reduced Three Dimensional Model for SAW Sensors Using Finite Element Analysis 2009-12-08 doi: 10.3390/s91209945 Mohamed M. El Gowini Walied A. Moussa http://www.mdpi.com/1424-8220/8/11/7438/ This paper discusses sputtered silicon encapsulation as a wafer level packaging approach for isolatable MEMS devices. Devices such as accelerometers, RF switches, inductors, and filters that do not require interaction with the surroundings to function, could thus be fully encapsulated at the wafer level after fabrication. A MEMSTech 50g capacitive accelerometer was used to demonstrate a sputtered encapsulation technique. Encapsulation with a very uniform surface profile was achieved using spin-on glass (SOG) as a sacrificial layer, SU-8 as base layer, RF sputtered silicon as main structural layer, eutectic gold-silicon as seal layer, and liquid crystal polymer (LCP) as outer encapsulant layer. SEM inspection and capacitance test indicated that the movable elements were released after encapsulation. Nanoindentation test confirmed that the encapsulated device is sufficiently robust to withstand a transfer molding process. Thus, an encapsulation technique that is robust, CMOS compatible, and economical has been successfully developed for packaging isolatable MEMS devices at the wafer level. http://www.mdpi.com/1424-8220/8/11/7438/ Wed, 19 Nov 2008 00:00:00 CET Sensors 2008-11-19 8 11 Article 7438 7452 1424-8220 Sputtered Encapsulation as Wafer Level Packaging for Isolatable MEMS Devices: A Technique Demonstrated on a Capacitive Accelerometer 2008-11-19 doi: 10.3390/s8117438 Azrul Azlan Hamzah Jumril Yunas Burhanuddin Yeop Majlis Ibrahim Ahmad http://www.mdpi.com/1424-8220/8/11/7359/ The polymer polyvinylidene difluoride (PVDF) has unique piezoelectric properties favorable for Micro-Electro-Mechanical Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS) applications. In the present research, we conducted nanometer-length scale characterization of this material using several high-resolution techniques. Specifically, we used an atomic force microscope (AFM) to study the nanoand microstructures of the PVDF under stress and to measure their nanoscale conductivity and piezoelectricity. We found that the surface morphology, electronic structure, and microstructure are profoundly affected under electrical potential. Such a behavior is important for the properties and performance of MEMS and NEMS. http://www.mdpi.com/1424-8220/8/11/7359/ Tue, 18 Nov 2008 00:00:00 CET Sensors 2008-11-18 8 11 Article 7359 7368 1424-8220 Nano-Scale Characterization of a Piezoelectric Polymer (Polyvinylidene Difluoride, PVDF) 2008-11-18 doi: 10.3390/s8117359 Hyungoo Lee Rodrigo Cooper Ke Wang Hong Liang http://www.mdpi.com/1424-8220/8/6/3706/ In a vertical type, vibratory gyroscope, the coupled motion between reference (driving) and sensing vibrations causes the zero-point output, which is the unwanted sensing vibration without angular velocity. This structural coupling leads to an inherent discrepancy between the natural frequencies of the reference and the sensing oscillations, causing curve veering in frequency loci. The coupled motion deteriorates sensing performance and dynamic stability. In this paper, the dynamic characteristics associated with the coupling phenomenon are theoretically analyzed. The effects of reference frequency and coupling factor on the rotational direction and amplitude of elliptic oscillation are determined. Based on the analytical studies on the coupling effects, we propose and fabricate a vertically decoupled vibratory gyroscope with the frequency matching. http://www.mdpi.com/1424-8220/8/6/3706/ Tue, 03 Jun 2008 00:00:00 CEST Sensors 2008-06-03 8 6 Article 3706 3718 1424-8220 Dynamic Characteristics of Vertically Coupled Structures and the Design of a Decoupled Micro Gyroscope 2008-06-03 doi: 10.3390/s8063706 Bumkyoo Choi Seung-Yop Lee Taekhyun Kim Seog Soon Baek http://www.mdpi.com/1424-8220/8/4/2240/ Global Navigation Satellite Systems (GNSS), such as the Global Positioning System (GPS), have been widely utilized and their applications are becoming popular, not only in military or commercial applications, but also for everyday life. Although GPS measurements are the essential information for currently developed land vehicle navigation systems (LVNS), GPS signals are often unavailable or unreliable due to signal blockages under certain environments such as urban canyons. This situation must be compensated in order to provide continuous navigation solutions. To overcome the problems of unavailability and unreliability using GPS and to be cost and size effective as well, Micro Electro Mechanical Systems (MEMS) based inertial sensor technology has been pushing for the development of low-cost integrated navigation systems for land vehicle navigation and guidance applications. This paper will analyze the characterization of MEMS based inertial sensors and the performance of an integrated system prototype of MEMS based inertial sensors, a low-cost GPS receiver and a digital compass. The influence of the stochastic variation of sensors will be assessed and modeled by two different methods, namely Gauss-Markov (GM) and AutoRegressive (AR) models, with GPS signal blockage of different lengths. Numerical results from kinematic testing have been used to assess the performance of different modeling schemes. http://www.mdpi.com/1424-8220/8/4/2240/ Sat, 29 Mar 2008 00:00:00 CET Sensors 2008-03-29 8 4 Article 2240 2261 1424-8220 Error and Performance Analysis of MEMS-based Inertial Sensors with a Low-cost GPS Receiver 2008-03-29 doi: 10.3390/s8042240 Minha Park Yang Gao http://www.mdpi.com/1424-8220/8/3/1475/ Modeling and simulation for heat and mass transport in micro channel are beingused extensively in researches and industrial applications to gain better understanding of thefundamental processes and to optimize fuel cell designs before building a prototype forengineering application. In this study, we used a single-phase, fully three dimensionalsimulation model for PEMFC that can deal with both anode and cathode flow field forexamining the micro flow channel with electrochemical reaction. The results show thathydrogen and oxygen were solely supplied to the membrane by diffusion mechanism ratherthan convection transport, and the higher pressure drop at cathode side is thought to becaused by higher flow rate of oxygen at cathode. And it is found that the amount of water incathode channel was determined by water formation due to electrochemical reaction pluselectro-osmotic mass flux directing toward the cathode side. And it is very important tomodel the back diffusion and electro-osmotic mass flux accurately since the two flux wasclosely correlated each other and greatly influenced for determination of ionic conductivityof the membrane which directly affects the performance of fuel cell. http://www.mdpi.com/1424-8220/8/3/1475/ Mon, 03 Mar 2008 00:00:00 CET Sensors 2008-03-03 8 3 Article 1475 1487 1424-8220 Three-Dimensional Transport Modeling for Proton Exchange Membrane(PEM) Fuel Cell with Micro Parallel Flow Field 2008-03-03 doi: 10.3390/s8031475 Pil Hyong Lee Sang Seok Han Sang Soon Hwang http://www.mdpi.com/1424-8220/8/2/1308/ For microfabrications of biochips with micro fluidic channels, a large number of microfabrication techniques based on silicon or glass-based Micro-Electro-Mechanical System (MEMS) technologies were proposed in the last decade. In recent years, for low cost and mass production, polymer-based microfabrication techniques by microinjection molding and micro hot embossing have been proposed. These techniques, which require a proper photoresist, mask, UV light exposure, developing, and electroplating as a preprocess, are considered to have some problems. In this study, we propose a new microfabrication technology which consists of micro end-milling and powder blasting. This technique could be directly applied to fabricate the metal mold without any preprocesses. The metal mold with micro-channels is machined by micro end-milling, and then, burrs generated in the end-milling process are removed by powder blasting. From the experimental results, micro end-milling combined with powder blasting could be applied effectively for fabrication of the injection mold of biochips with micro fluidic channels. http://www.mdpi.com/1424-8220/8/2/1308/ Fri, 22 Feb 2008 00:00:00 CET Sensors 2008-02-22 8 2 Article 1308 1320 1424-8220 Fabrication of Biochips with Micro Fluidic Channels by Micro End-milling and Powder Blasting 2008-02-22 doi: 10.3390/s8021308 Dae Jin Yun Tae Il Seo Dong Sam Park http://www.mdpi.com/1424-8220/8/2/994/ In this paper, a finite element (FE) procedure for modeling electrostatically actu-ated MEMS is presented. It concerns a perturbation method for computing electrostatic fielddistortions due to moving conductors. The computation is split in two steps. First, an un-perturbed problem (in the absence of certain conductors) is solved with the conventional FEmethod in the complete domain. Second, a perturbation problem is solved in a reduced re-gion with an additional conductor using the solution of the unperturbed problem as a source.When the perturbing region is close to the original source field, an iterative computation maybe required. The developed procedure offers the advantage of solving sub-problems in re-duced domains and consequently of benefiting from different problem-adapted meshes. Thisapproach allows for computational efficiency by decreasing the size of the problem. http://www.mdpi.com/1424-8220/8/2/994/ Tue, 19 Feb 2008 00:00:00 CET Sensors 2008-02-19 8 2 Article 994 1003 1424-8220 A Perturbation Method for the 3D Finite Element Modeling of Electrostatically Driven MEMS 2008-02-19 doi: 10.3390/s8020994 Mohamed Boutaayamou Ruth V. Sabariego Patrick Dular http://www.mdpi.com/1424-8220/8/2/1048/ We study the influence of von Karman nonlinearity, van der Waals force, and a athermal stresses on pull-in instability and small vibrations of electrostatically actuated mi-croplates. We use the Galerkin method to develop a tractable reduced-order model for elec-trostatically actuated clamped rectangular microplates in the presence of van der Waals forcesand thermal stresses. More specifically, we reduce the governing two-dimensional nonlineartransient boundary-value problem to a single nonlinear ordinary differential equation. For thestatic problem, the pull-in voltage and the pull-in displacement are determined by solving apair of nonlinear algebraic equations. The fundamental vibration frequency corresponding toa deflected configuration of the microplate is determined by solving a linear algebraic equa-tion. The proposed reduced-order model allows for accurately estimating the combined effectsof van der Waals force and thermal stresses on the pull-in voltage and the pull-in deflectionprofile with an extremely limited computational effort. http://www.mdpi.com/1424-8220/8/2/1048/ Fri, 15 Feb 2008 00:00:00 CET Sensors 2008-02-15 8 2 Article 1048 1069 1424-8220 Effects of van der Waals Force and Thermal Stresses on Pull-in Instability of Clamped Rectangular Microplates 2008-02-15 doi: 10.3390/s8021048 Romesh C. Batra Maurizio Porfiri Davide Spinello http://www.mdpi.com/1424-8220/8/2/877/ This study is to develop a micromachining technology for a light guidepanel(LGP) mold, whereby micro dot patterns are formed on a LGP surface by a singleinjection process instead of existing screen printing processes. The micro powder blastingtechnique is applied to form micro dot patterns on the LGP mold surface. The optimalconditions for masking, laminating, exposure, and developing processes to form the microdot patterns are first experimentally investigated. A LGP mold with masked micro patternsis then machined using the micro powder blasting method and the machinability of themicro dot patterns is verified. A prototype LGP is test- injected using the developed LGPmold and a shape analysis of the patterns and performance testing of the injected LGP arecarried out. As an additional approach, matte finishing, a special surface treatment method,is applied to the mold surface to improve the light diffusion characteristics, uniformity andbrightness of the LGP. The results of this study show that the applied powder blastingmethod can be successfully used to manufacture LGPs with micro patterns by just singleinjection using the developed mold and thereby replace existing screen printing methods. http://www.mdpi.com/1424-8220/8/2/877/ Fri, 08 Feb 2008 00:00:00 CET Sensors 2008-02-08 8 2 Article 877 885 1424-8220 Micro Dot Patterning on the Light Guide Panel Using Powder Blasting 2008-02-08 doi: 10.3390/s8020877 Ho Su Jang Myeong Woo Cho Dong Sam Park http://www.mdpi.com/1424-8220/8/2/784/ With increasing demands for wireless sensing nodes for assets control and condition monitoring; needs for alternatives to expensive conventional accelerometers in vibration measurements have been arisen. Micro-Electro Mechanical Systems (MEMS) accelerometer is one of the available options. The performances of three of the MEMS accelerometers from different manufacturers are investigated in this paper and compared to a well calibrated commercial accelerometer used as a reference for MEMS sensors performance evaluation. Tests were performed on a real CNC machine in a typical industrial environmental workshop and the achieved results are presented. http://www.mdpi.com/1424-8220/8/2/784/ Wed, 06 Feb 2008 00:00:00 CET Sensors 2008-02-06 8 2 Article 784 799 1424-8220 Suitability of MEMS Accelerometers for Condition Monitoring: An experimental study 2008-02-06 doi: 10.3390/s8020784 Alhussein Albarbar Samir Mekid Andrew Starr Robert Pietruszkiewicz http://www.mdpi.com/1424-8220/8/2/767/ The dynamic characterization of a set of gold micro beams by electrostatic excitation in presence of residual stress gradient has been studied experimentally. A method to determine the micro-cantilever residual stress gradient by measuring the deflection and curvature and then identifying the residual stress model by means of frequency shift behaviour is presented. A comparison with different numerical FEM models and experimental results has been carried out, introducing in the model the residual stress of the structures, responsible for an initial upward curvature. Dynamic spectrum data are measured via optical interferometry and experimental frequency shift curves are obtained by increasing the dc voltage applied to the specimens. A good correspondence is pointed out between measures and numerical models so that the residual stress effect can be evaluated for different configurations. http://www.mdpi.com/1424-8220/8/2/767/ Wed, 06 Feb 2008 00:00:00 CET Sensors 2008-02-06 8 2 Article 767 783 1424-8220 Experimental-Numerical Comparison of the Cantilever MEMS Frequency Shift in presence of a Residual Stress Gradient 2008-02-06 doi: 10.3390/s8020767 Alberto Ballestra Aurelio Somà Renato Pavanello http://www.mdpi.com/1424-8220/8/2/700/ In this study, micro fluid channels are machined on fused silica glass via powder blasting, a mechanical etching process, and the machining characteristics of the channels are experimentally evaluated. In the process, material removal is performed by the collision of micro abrasives injected by highly compressed air on to the target surface. This approach can be characterized as an integration of brittle mode machining based on micro crack propagation. Fused silica glass, a high purity synthetic amorphous silicon dioxide, is selected as a workpiece material. It has a very low thermal expansion coefficient and excellent optical qualities and exceptional transmittance over a wide spectral range, especially in the ultraviolet range. The powder blasting process parameters affecting the machined results are injection pressure, abrasive particle size and density, stand-off distance, number of nozzle scanning, and shape/size of the required patterns. In this study, the influence of the number of nozzle scanning, abrasive particle size, and pattern size on the formation of micro channels is investigated. Machined shapes and surface roughness are measured using a 3-dimensional vision profiler and the results are discussed. http://www.mdpi.com/1424-8220/8/2/700/ Wed, 06 Feb 2008 00:00:00 CET Sensors 2008-02-06 8 2 Article 700 710 1424-8220 Micro Fluidic Channel Machining on Fused Silica Glass Using Powder Blasting 2008-02-06 doi: 10.3390/s8020700 Ho-Su Jang Myeong-Woo Cho Dong-Sam Park http://www.mdpi.com/1424-8220/8/1/222/ Recently, the magnetorheological (MR) polishing process has been examined asa new ultra-precision polishing technology for micro parts in MEMS applications. In theMR polishing process, the magnetic force plays a dominant role. This method uses MRfluids which contains micro abrasives as a polishing media. The objective of the presentresearch is to shed light onto the material removal mechanism under various slurryconditions for polishing and to investigate surface characteristics, including shape analysisand surface roughness measurement, of spots obtained from the MR polishing process usingalumina abrasives. A series of basic experiments were first performed to determine theoptimum polishing conditions for BK7 glass using prepared slurries by changing the processparameters, such as wheel rotating speed and electric current. Using the obtained results,groove polishing was then performed and the results are investigated. Outstanding surfaceroughness of Ra=3.8nm was obtained on the BK7 glass specimen. The present resultshighlight the possibility of applying this polishing method to ultra-precision micro partsproduction, especially in MEMS applications. http://www.mdpi.com/1424-8220/8/1/222/ Mon, 21 Jan 2008 00:00:00 CET Sensors 2008-01-21 8 1 Article 222 235 1424-8220 Experimental Study on the Effects of Alumina Abrasive Particle Behavior in MR Polishing for MEMS Applications 2008-01-21 doi: 10.3390/s8010222 Dong-Woo Kim Myeong-Woo Cho Tae-Il Seo Young-Jae Shin http://www.mdpi.com/1424-8220/8/1/211/ Micro drilled holes are utilized in many of today’s fabrication processes.Precision production processes in industries are trending toward the use of smaller holeswith higher aspect ratios, and higher speed operation for micro deep hole drilling. However,undesirable characteristics related to micro drilling such as small signal-to-noise ratios,wandering drill motion, high aspect ratio, and excessive cutting forces can be observedwhen cutting depth increases. In this study, the authors attempt to minimize the thrustforces in the step-feed micro drilling process by application of the DOE (Design ofExperiment) method. Taking into account the drilling thrust, three cutting parameters,feedrate, step-feed, and cutting speed, are optimized based on the DOE method. Forexperimental studies, an orthogonal array L27(313) is generated and ANOVA (Analysis ofVariance) is carried out. Based on the results it is determined that the sequence of factorsaffecting drilling thrusts corresponds to feedrate, step-feed, and spindle rpm. Acombination of optimal drilling conditions is also identified. In particular, it is found in thisstudy that the feedrate is the most important factor for micro drilling thrust minimization. http://www.mdpi.com/1424-8220/8/1/211/ Mon, 21 Jan 2008 00:00:00 CET Sensors 2008-01-21 8 1 Article 211 221 1424-8220 Application of Design of Experiment Method for Thrust Force Minimization in Step-feed Micro Drilling 2008-01-21 doi: 10.3390/s8010211 Dong-Woo Kim Myeong-Woo Cho Tae-il Seo Eung-Sug Lee http://www.mdpi.com/1424-8220/7/12/3071/ In this paper a four-mirror tunable micro electro-mechanical systems (MEMS)Fabry Perot Interferometer (FPI) concept is proposed with the mathematical model. Thespectral range of the proposed FPI lies in the infrared spectrum ranging from 2400 to 4018(nm). FPI can be finely tuned by deflecting the two middle mirrors (or by changing the threecavity lengths). Two different cases were separately considered for the tuning. In case one,tuning was achieved by deflecting mirror 2 only and in case two, both mirrors 2 and 3 weredeflected for the tuning of the FPI. http://www.mdpi.com/1424-8220/7/12/3071/ Tue, 04 Dec 2007 00:00:00 CET Sensors 2007-12-04 7 12 Communication 3071 3083 1424-8220 Three Cavity Tunable MEMS Fabry Perot Interferometer 2007-12-04 doi: 10.3390/s7123071 Avinash Parashar Ankur Shah Muthukumaran Packirisamy Narayanswamy Sivakumar http://www.mdpi.com/1424-8220/7/12/3012/ The influence of damping on the dynamical behavior of the electrostaticparallel-plate and torsional actuators with the van der Waals (vdW) or Casimir force(torque) is presented. The values of the pull-in parameters and the number of theequilibrium points do not change whether there is damping or not. The ability ofequilibrium points is varied with the appearance of damping. One equilibrium point is anunstable saddle with a different damping coefficient, the other equilibrium point is astable node when the damping coefficient is greater than some critical value, andotherwise it is a stable focus. Then there are two heteroclinic orbits passing from theunstable saddle point to the stable node or focus. http://www.mdpi.com/1424-8220/7/12/3012/ Thu, 29 Nov 2007 00:00:00 CET Sensors 2007-11-29 7 12 Article 3012 3026 1424-8220 Influence of Damping on the Dynamical Behavior of the Electrostatic Parallel-plate and Torsional Actuators with Intermolecular Forces 2007-11-29 doi: 10.3390/s7123012 Wen-Hui Lin Ya-Pu Zhao http://www.mdpi.com/1424-8220/7/11/2997/ This paper investigates the effect of electrical contact on the thermal contactstress of a microrelay switch. A three-dimensional elastic-plastic finite element model withcontact elements is used to simulate the contact behavior between the microcantilever beamand the electrode. A model with thermal-electrical coupling and thermal-stress coupling isused in the finite element analysis. The effects of contact gap, plating film thickness andnumber of switching cycles on the contact residual stress, contact force, plastic deformation,and temperature rise of the microrelay switch are explored. The numerical results indicatethat the residual stress increases with increasing contact gap or decreasing plating filmthickness. The results also show that the residual stress increases as the number of switchingcycles increases. A large residual stress inside the microcantilever beam can decrease thelifecycle of the microrelay. http://www.mdpi.com/1424-8220/7/11/2997/ Mon, 26 Nov 2007 00:00:00 CET Sensors 2007-11-26 7 11 Article 2997 3011 1424-8220 Effect of Electrical Contact on the Contact Residual Stress of a Microrelay Switch 2007-11-26 doi: 10.3390/s7112997 Yung-Chuan Chen Hsun-Heng Tsai Wei-Hua Lu Li-Wen Chen http://www.mdpi.com/1424-8220/7/11/2846/ Quantitative Accelerated Life Testing (QALT) is a solution for assessing thereliability of Micro Electro Mechanical Systems (MEMS). A procedure for QALT is shownin this paper and an attempt to assess the reliability level for a batch of MEMSaccelerometers is reported. The testing plan is application-driven and contains combinedtests: thermal (high temperature) and mechanical stress. Two variants of mechanical stressare used: vibration (at a fixed frequency) and tilting. Original equipment for testing at tiltingand high temperature is used. Tilting is appropriate as application-driven stress, because thetilt movement is a natural environment for devices used for automotive and aerospaceapplications. Also, tilting is used by MEMS accelerometers for anti-theft systems. The testresults demonstrated the excellent reliability of the studied devices, the failure rate in the“worst case” being smaller than 10-7h-1. http://www.mdpi.com/1424-8220/7/11/2846/ Tue, 20 Nov 2007 00:00:00 CET Sensors 2007-11-20 7 11 Article 2846 2859 1424-8220 Quantitative Accelerated Life Testing of MEMS Accelerometers 2007-11-20 doi: 10.3390/s7112846 Marius Bâzu Lucian Gălăţeanu Virgil Emil Ilian Jerome Loicq Serge Habraken Jean-Paul Collette http://www.mdpi.com/1424-8220/7/12/3386/ This paper presents the simulation, fabrication and characterization of a microFET (field effect transistor) pressure sensor with readout circuits. The pressure sensorincludes 16 sensing cells in parallel. Each sensing cell that is circular shape is composed ofan MOS (metal oxide semiconductor) and a suspended membrane, which the suspendedmembrane is the movable gate of the MOS. The CoventorWare is used to simulate thebehaviors of the pressure sensor, and the HSPICE is employed to evaluate the characteristicsof the circuits. The pressure sensor integrated with circuits is manufactured using thecommercial 0.35 μm CMOS (complementary metal oxide semiconductor) process and apost-process. In order to obtain the suspended membranes, the pressure sensor requires apost-CMOS process. The post-process adopts etchants to etch the sacrificial layers in thepressure sensors to release the suspended membranes, and then the etch holes in the pressuresensor are sealed by LPCVD (low pressure chemical vapor deposition) parylene. Thepressure sensor produces a change in current when applying a pressure to the sensing cells.The circuits are utilized to convert the current variation of the pressure sensor into thevoltage output. Experimental results show that the pressure sensor has a sensitivity of 0.032mV/kPa in the pressure range of 0-500 kPa. http://www.mdpi.com/1424-8220/7/12/3386/ Mon, 19 Nov 2007 00:00:00 CET Sensors 2007-11-19 7 12 Article 3386 3398 1424-8220 Modeling and Fabrication of Micro FET Pressure Sensor with Circuits 2007-11-19 doi: 10.3390/s7123386 Ching-Liang Dai Yao-Wei Tai Pin-Hsu Kao http://www.mdpi.com/1424-8220/7/11/2660/ This study presents the simulation, fabrication and characterization ofmicromechanical radio frequency (RF) switch with micro inductors. The inductors areemployed to enhance the characteristic of the RF switch. An equivalent circuit model isdeveloped to simulate the performance of the RF switch. The behaviors of themicromechanical RF switch are simulated by the finite element method software,CoventorWare. The micromechanical RF switch is fabricated using the complementarymetal oxide semiconductor (CMOS) and a post-process. The post-process employs a wetetching to etch the sacrificial layer, and to release the suspended structures of the RF switch.The structure of the RF switch contains a coplanar waveguide (CPW), a suspendedmembrane, eight springs and two inductors in series. Experimental results reveal that theinsertion loss and isolation of the switch are 1.7 dB at 21 GHz and 19 dB at 21 GHz,respectively. The driving voltage of the switch is about 13 V. http://www.mdpi.com/1424-8220/7/11/2660/ Fri, 09 Nov 2007 00:00:00 CET Sensors 2007-11-09 7 11 Article 2660 2670 1424-8220 Modeling and Manufacturing of Micromechanical RF Switch with Inductors 2007-11-09 doi: 10.3390/s7112670 Ching-Liang Dai Ying-Liang Chen http://www.mdpi.com/1424-8220/7/10/2174/ We have developed a wireless-controlled compact optical switch by siliconmicromachining techniques with DC magnetron sputtering. For the optical switchingoperation, micro mirror is designed as cantilever shape size of 5mm×800μm×50μm.TbDyFe film is sputter-deposited on the upper side of the mirror with the condition as: Argas pressure below 1.2×10-9 torr, DC input power of 180W and heating temperature of up to250°C for the wireless control of each component. Mirrors are actuated by externallyapplied magnetic fields for the micro application. Applied beam path can be changedaccording to the direction and the magnitude of applied magnetic field. Reflectivity changes,M-H curves and X-ray diffractions of sputtered mirrors are measured to determine magneto-optical, magneto-elastic properties with variation in sputtered film thickness. The deflectedangle-magnetic field characteristics of the fabricated mirror are measured. http://www.mdpi.com/1424-8220/7/10/2174/ Tue, 09 Oct 2007 00:00:00 CEST Sensors 2007-10-09 7 10 Article 2174 2182 1424-8220 Magnetostrictive Micro Mirrors for an Optical Switch Matrix 2007-10-09 doi: 10.3390/s7102174 Heung-Shik Lee Chongdu Cho Myeong-Woo Cho http://www.mdpi.com/1424-8220/7/9/1887/ Some shape memory alloys like NiTi show noticeable high damping property inpseudoelastic range. Due to its unique characteristics, a NiTi alloy is commonly used forpassive damping applications, in which the energy may be dissipated by the conversion frommechanical to thermal energy. This study presents a shape memory alloy based micro-damper, which exploits the pseudoelasticity of NiTi wires for energy dissipation. Themechanical model and functional principle of the micro-damper are explained in detail.Moreover, the mechanical behavior of NiTi wires subjected to various temperatures, strainrates and strain amplitudes is observed. Resulting from those experimental results, thedamping properties of the micro-damper involving secant stiffness, energy dissipation andloss factor are analyzed. The result indicates the proposed NiTi based micro-damper exhibitsgood energy dissipation ability, compared with conventional materials damper. http://www.mdpi.com/1424-8220/7/9/1887/ Tue, 11 Sep 2007 00:00:00 CEST Sensors 2007-09-11 7 9 Article 1887 1900 1424-8220 The Investigation of a Shape Memory Alloy Micro-Damper for MEMS Applications 2007-09-11 doi: 10.3390/s7091887 Qiang Pan Chongdu Cho http://www.mdpi.com/1424-8220/7/9/1817/ The effect of accidental drops on MEMS sensors are examined within the frame-work of a multi-scale finite element approach. With specific reference to a polysilicon MEMSaccelerometer supported by a naked die, the analysis is decoupled into macro-scale (at dielength-scale) and meso-scale (at MEMS length-scale) simulations, accounting for the verysmall inertial contribution of the sensor to the overall dynamics of the device. Macro-scaleanalyses are adopted to get insights into the link between shock waves caused by the impactagainst a target surface and propagating inside the die, and the displacement/acceleration his-tories at the MEMS anchor points. Meso-scale analyses are adopted to detect the most stresseddetails of the sensor and to assess whether the impact can lead to possible localized failures.Numerical results show that the acceleration at sensor anchors cannot be considered an ob-jective indicator for drop severity. Instead, accurate analyses at sensor level are necessary toestablish how MEMS can fail because of drops. http://www.mdpi.com/1424-8220/7/9/1817/ Fri, 07 Sep 2007 00:00:00 CEST Sensors 2007-09-07 7 9 Article 1817 1833 1424-8220 Multi-scale Analysis of MEMS Sensors Subject to Drop Impacts 2007-09-07 doi: 10.3390/s7081817 Stefano Mariani Aldo Ghisi Alberto Corigliano Sarah Zerbini http://www.mdpi.com/1424-8220/7/9/1720/ In this paper, we report spring corner designs and driving waveforms to improve the reliability for a MEMS (Micro-Electro-Mechanical System) actuator. In order to prevent the stiction problems, no stopper or damping absorber is adopted. Therefore, an actuator could travel long distance by electromagnetic force without any object in moving path to absorb excess momentum. Due to long displacement and large mass, springs of MEMS actuators tend to crack from weak points with high stress concentration and this situation degrades reliability performance. Stress distribution over different spring designs were simulated and a serpentine spring with circular and wide corner design was chosen due to its low stress concentration. This design has smaller stress concentration versus displacement. Furthermore, the resonant frequencies are removed from the driving waveform based on the analysis of discrete Fourier transfer function. The reshaped waveform not only shortens actuator switching time, but also ensures that the spring is in a small displacement region without overshooting so that the maximum stress is kept below 200 MPa. The experimental results show that the MEMS device designed by theses principles can survive 500 g (gravity acceleration) shock test and pass 150 million switching cycles without failure. http://www.mdpi.com/1424-8220/7/9/1720/ Mon, 03 Sep 2007 00:00:00 CEST Sensors 2007-09-03 7 9 Article 1720 1730 1424-8220 Reliability of a MEMS Actuator Improved by Spring Corner Designs and Reshaped Driving Waveforms 2007-09-03 doi: 10.3390/s7091720 Hsin-Ta Hsieh Guo-Dung John Su http://www.mdpi.com/1424-8220/7/8/1643/ Recently, the polymeric micro-fluidic biochip, often called LOC (lab-on-a-chip), has been focused as a cheap, rapid and simplified method to replace the existing biochemical laboratory works. It becomes possible to form miniaturized lab functionalities on a chip with the development of MEMS technologies. The micro-fluidic chips contain many micro-channels for the flow of sample and reagents, mixing, and detection tasks. Typical substrate materials for the chip are glass and polymers. Typical techniques for micro-fluidic chip fabrication are utilizing various micro pattern forming methods, such as wet-etching, micro-contact printing, and hot-embossing, micro injection molding, LIGA, and micro powder blasting processes, etc. In this study, to establish the basis of the micro pattern fabrication and mass production of polymeric micro-fluidic chips using injection molding process, micro machining method was applied to form micro-channels on the LOC molds. In the research, a series of machining experiments using micro end-mills were performed to determine optimum machining conditions to improve surface roughness and shape accuracy of designed simplified micro-channels. Obtained conditions were used to machine required mold inserts for micro-channels using micro end-mills. Test injection processes using machined molds and COC polymer were performed, and then the results were investigated. http://www.mdpi.com/1424-8220/7/8/1643/ Mon, 27 Aug 2007 00:00:00 CEST Sensors 2007-08-27 7 8 Article 1643 1654 1424-8220 Micro Machining of Injection Mold Inserts for Fluidic Channel of Polymeric Biochips 2007-08-27 doi: 10.3390/s7081643 Woo-Chul Jung Young-Moo Heo Gil-Sang Yoon Kwang-Ho Shin Sung-Ho Chang Gun-Hee Kim Myeong-Woo Cho http://www.mdpi.com/1424-8220/7/8/1399/ Incorporating the velocity slip effect of the gas flow at the solid boundary, theperformance and dynamic response of a micro gas-bearing-rotor system are investigated inthis paper. For the characteristic length scale of the micro gas bearing, the gas flow in thebearing resides in the slip regime rather than in the continuum regime. The modifiedReynolds equations of different slip models are presented. Gas pressure distribution and loadcarrying capacity are obtained by solving the Reynolds equations with finite differentmethod (FDM). Comparing results from different models, it is found that the second orderslip model agrees reasonably well with the benchmarked solutions obtained from thelinearized Boltzmann equation. Therefore, dynamic coefficients derived from the secondorder slip model are employed to evaluate the linear dynamic stability and vibrationcharacteristics of the system. Compared with the continuum flow model, the slip effectreduces dynamic coefficients of the micro gas bearing, and the threshold speed for stableoperation is consequently raised. Also, dynamic analysis shows that the system responseschange with variation of the operating parameters including the eccentricity ratio, therotational speed, and the unbalance ratio. http://www.mdpi.com/1424-8220/7/8/1399/ Fri, 03 Aug 2007 00:00:00 CEST Sensors 2007-08-03 7 8 Article 1399 1414 1424-8220 Investigations of Slip Effect on the Performance of Micro Gas Bearings and Stability of Micro Rotor-Bearing Systems 2007-08-03 doi: 10.3390/s7081399 Hai Huang Guang Meng Jieyu Chen http://www.mdpi.com/1424-8220/7/8/1387/ This paper presents the integration of an inductor by complementary metal-oxide-semiconductor (CMOS) compatible processes for integrated smart microsensorsystems that have been developed to monitor the motion and vital signs of humans invarious environments. Integration of radio frequency transmitter (RF) technology withcomplementary metal-oxide-semiconductor/micro electro mechanical systems (CMOS/MEMS) microsensors is required to realize the wireless smart microsensors system. Theessential RF components such as a voltage controlled RF-CMOS oscillator (VCO), spiralinductors for an LC resonator and an integrated antenna have been fabricated and evaluatedexperimentally. The fabricated RF transmitter and integrated antenna were packaged withsubminiature series A (SMA) connectors, respectively. For the impedance (50 ) matching,a bonding wire type inductor was developed. In this paper, the design and fabrication of thebonding wire inductor for impedance matching is described. Integrated techniques for theRF transmitter by CMOS compatible processes have been successfully developed. Aftermatching by inserting the bonding wire inductor between the on-chip integrated antennaand the VCO output, the measured emission power at distance of 5 m from RF transmitterwas -37 dBm (0.2 μW). http://www.mdpi.com/1424-8220/7/8/1387/ Tue, 31 Jul 2007 00:00:00 CEST Sensors 2007-07-31 7 8 Article 1387 1398 1424-8220 Integrated Inductors for RF Transmitters in CMOS/MEMS Smart Microsensor Systems 2007-07-31 doi: 10.3390/s7081387 Jong-Wan Kim Hidekuni Takao Kazuaki Sawada Makoto Ishida http://www.mdpi.com/1424-8220/7/7/1069/ We present a straightforward method to solve gas damping problems for perfo-rated structures in two dimensions (2D) utilising a Perforation Profile Reynolds (PPR) solver.The PPR equation is an extended Reynolds equation that includes additional terms modellingthe leakage flow through the perforations, and variable diffusivity and compressibility pro-files. The solution method consists of two phases: 1) determination of the specific admittanceprofile and relative diffusivity (and relative compressibility) profiles due to the perforation,and 2) solution of the PPR equation with a FEM solver in 2D. Rarefied gas corrections inthe slip-flow region are also included. Analytic profiles for circular and square holes withslip conditions are presented in the paper. To verify the method, square perforated damperswith 16 – 64 holes were simulated with a three-dimensional (3D) Navier-Stokes solver, a ho-mogenised extended Reynolds solver, and a 2D PPR solver. Cases for both translational (innormal to the surfaces) and torsional motion were simulated. The presented method extendsthe region of accurate simulation of perforated structures to cases where the homogenisationmethod is inaccurate and the full 3D Navier-Stokes simulation is too time-consuming. http://www.mdpi.com/1424-8220/7/7/1069/ Thu, 28 Jun 2007 00:00:00 CEST Sensors 2007-06-28 7 7 Article 1069 1090 1424-8220 Methods for Solving Gas Damping Problems in Perforated Microstructures Using a 2D Finite-Element Solver 2007-06-28 doi: 10.3390/s7071069 Timo Veijola Peter Raback http://www.mdpi.com/1424-8220/7/5/760/ Electrostatic micro-electro-mechanical system (MEMS) is a special branch with a wide range of applications in sensing and actuating devices in MEMS. This paper provides a survey and analysis of the electrostatic force of importance in MEMS, its physical model, scaling effect, stability, nonlinearity and reliability in detail. It is necessary to understand the effects of electrostatic forces in MEMS and then many phenomena of practical importance, such as pull-in instability and the effects of effective stiffness, dielectric charging, stress gradient, temperature on the pull-in voltage, nonlinear dynamic effects and reliability due to electrostatic forces occurred in MEMS can be explained scientifically, and consequently the great potential of MEMS technology could be explored effectively and utilized optimally. A simplified parallel-plate capacitor model is proposed to investigate the resonance response, inherent nonlinearity, stiffness softened effect and coupled nonlinear effect of the typical electrostatically actuated MEMS devices. Many failure modes and mechanisms and various methods and techniques, including materials selection, reasonable design and extending the controllable travel range used to analyze and reduce the failures are discussed in the electrostatically actuated MEMS devices. Numerical simulations and discussions indicate that the effects of instability, nonlinear characteristics and reliability subjected to electrostatic forces cannot be ignored and are in need of further investigation. http://www.mdpi.com/1424-8220/7/5/760/ Thu, 31 May 2007 00:00:00 CEST Sensors 2007-05-31 7 5 Article 760 796 1424-8220 Stability, Nonlinearity and Reliability of Electrostatically Actuated MEMS Devices 2007-05-31 doi: 10.3390/s7050760 Wen-Ming Zhang Guang Meng Di Chen http://www.mdpi.com/1424-8220/7/5/697/ This study investigated the feasibility of the micro powder blasting technique for the micro fabrication of sensor structures using the Pyrex glass to replace the existing silicon-based acceleration sensor fabrication processes. As the preliminary experiments, the effects of the blasting pressure, the mass flow rate of abrasive and the number of nozzle scanning times on erosion depth of the Pyrex and the soda lime glasses were examined. From the experimental results, optimal blasting conditions were selected for the Pyrex glass machining. The dimensions of the designed glass sensor was 1.7×1.7×0.6mm for the vibrating mass, and 2.9×0.7×0.2mm for the cantilever beam. The machining results showed that the dimensional errors of the machined glass sensor ranged from 3 μm in minimum to 20 μm in maximum. These results imply that the micro powder blasting method can be applied for the micromachining of glass-based acceleration sensors to replace the exiting method. http://www.mdpi.com/1424-8220/7/5/697/ Thu, 24 May 2007 00:00:00 CEST Sensors 2007-05-24 7 5 Article 697 707 1424-8220 An Experimental Study on the Fabrication of Glass-based Acceleration Sensor Body Using Micro Powder Blasting Method 2007-05-24 doi: 10.3390/s7050697 Dong-Sam Park Dae-Jin Yun Myeong-Woo Cho Bong-Cheol Shin