Investigation of air damping effect in two kinds of capacitive MEMS accelerometers

Microsystem Technologies - In this study, the air damping ratios of an unsealed chip of a capacitive accelerometer subjected to different pressures were measured by a special designed circuit in a...     

Reduction of squeeze-film damping in a wafer-level encapsulated RF MEMS DC shunt switch

This paper presents the design, fabrication and characterization aspects of a wafer-level encapsulated RF MEMS shunt switch with a perforated base substrate and a corrugated diaphragm. A three-wafer stacking concept was proposed to achieve a RF MEMS shunt switch based on metal-metal contact. The introduction of damping holes in the base substrate wafer is proven to be an effective way to reduce squeeze-film damping and thus increase the switching speed of the switch. It is also demonstrated by analytical calculation that some factors play important roles on the damping characteristics, such as the physical location of damping holes in the base substrate, hole size, and number of holes per radius ring. By means of the implementation of damping holes, the pull-in and release time of the fabricated MEMS switch are significantly reduced by about 13 times, from 5.4 ms to 0.435 ms and 40.6 ms to 3.2 ms, respectively.     

Modeling and analysis of MEMS disk resonators

Microsystem Technologies - In this work a very accurate process for modeling a microdisk resonator is presented and the dynamic behavior of the resonator is investigated. Using the minimization of...     

Modelling the effect of demand variations on the performance of a production system

Modelling the effect of demand variations on a production system manufacturing multiple products is discussed. The various system costs involved in the production system, namely set-up cost and inventory cost incurred due to change in demands for the products with respect to products and planning periods are estimated. A statistical modelling is presented for determining the production capacity and inventory level requirement to satisfy the customer to a certain level decided by the management. Two important factors, (i) number of types of products and (ii) multiple planning horizons are considered to identify the costs as well as the production capacity and inventory level requirements. A statistical method, analysis of variance (ANOVA) is used to study the variations in the demands and costs involved. Finally, an example is presented to explain the application and the behaviour of the statistical model.     

Quantifying adsorbed water monolayers on silicon MEMS resonators exposed to humid environments

This study investigated the influence of temperature and humidity on the adsorbed water layer on micron-scale monocrystalline silicon (Si) films in air, using a Si-MEMS kHz-frequency resonator. Both temperature and relative humidity induced a reversible change in resonant frequency, attributed to the temperature-dependent properties of Si and to a change in adsorbed water layer. The excellent precision in resonant frequency measurement (0.02 Hz, or 0.5 ppm) allowed precise calculation of the changes in adsorbed water layer thickness over the specimen surface. The increase in water thickness with relative humidity was a function of temperature and could not be described with simple multimolecular adsorption theories such as the BET theory. A likely explanation is the presence of hydrocarbon contaminants on the Si surface. Guidelines are provided to accurately measure the influence of temperature and relative humidity on the adsorbed water layer thickness on micron-scale Si surfaces, using this technique.     

Study of dynamic characteristics of resonators for MEMS resonant vibratory gyroscopes

Dynamic characteristics of resonators for MEMS resonant vibratory gyroscopes are studied in this paper. Firstly, a small parameter method is introduced to analyze the dynamic characteristic stability of the resonator. It is proved that geometrical parameters of the resonator have to be regulated to match corresponding stability analysis. In order to verify the rationality of the theoretical parameters design, static calibration experiment is built using a resonator sample. It is concluded from the calibrated result that the error between theory design and experiment is 0.03?%, which shows they have a good match, and the design of resonator is reasonable. Moreover, the method of small parameter perturbation is considered to analyze the input–output dynamic characteristic. Under some transformations, which make input angular velocity and output resonant frequency shift possess a good linear relationship. In order to verify the correctness of the theory analysis method, dynamic frequency output characteristic experiment is built using the resonant vibratory gyroscope sample. It is concluded from the dynamic measurement result that the correlation coefficient of output fitted curve is 99.95?%, the measured algorithm scale factor of the gyroscope sample is 0.2116, which prove theoretical analyzing approach is feasible.     

Improvement of damping performance by splitting damping material

Damping materials in the carriage arm of a hard disk drive reduce flow-induced vibrations. As recording tracks become narrower, better damping is required. In this paper, a technique of splitting damping materials to improve the damping performance is described. We assumed a structural damping and examined the damping performance using the strain energy stored in a viscoelastic material. At first, we classified deformations of the viscoelastic material into three kinds: bending, shearing and thickness deformation (change in thickness). For the bending and the shearing deformation, we clarified that the splitting technique does not increase the strain energy. For the thickness deformation, we derived equations for the deformation shape and the strain energy. Then we found the splitting increases the strain energy if the parameter ϕ, which is proportional to the length and related to the stiffness of the damping material, is more than 5. Finally, we demonstrated the effectiveness of the splitting technique by numerical simulations and experiments.     

Experimental validation of compact damping models of perforated MEMS devices

Measured damping coefficients of six different perforated micromechanical test structures are compared with damping coefficients given by published compact models. The motion of the perforated plates is almost translational, the surface shape is rectangular, and the perforation is uniform validating the assumptions made for compact models. In the structures, the perforation ratio varies from 24 to 59%. The study of the structure shows that the compressibility and inertia do not contribute to the damping at the frequencies used (130–220 kHz). The damping coefficients given by all four compact models underestimate the measured damping coefficient by approximately 20%. The reasons for this underestimation are discussed by studying the various flow components in the models.     

Effects of package on the performance of MEMS piezoresistive accelerometers

Package is one of the key technologies for MEMS accelerometers. This paper investigated the influence of package on performances of custom-designed MEMS piezoresistive accelerometer. Based on the designed package process, the effect of die adhesive and potting materials on the sensor sensitivity and residual stress were studied by theory analysis and experimental test. The results showed that: with more quantity of die adhesive when the thickness was fixed, the sensitivity of MEMS piezoresistive accelerometer was much smaller; in addition, with thicker die adhesive, the accelerometer had much bigger sensitivity and much smaller residual stress increment after the die attach process. Meanwhile, the sensitivity was proportional to the density of potting material, and it varied with the elastic modulus.     

Synchronization of uncertain MEMS resonators via adaptive time-varying terminal sliding mode control

Microsystem Technologies - The main goal of this study addresses the synchronization between two MEMS resonators with cubic and quintic mechanical stiffness under the existence of system...     

MEMS器件真空封装模型模拟

结合典型的MEMS器件真空封装工艺,应用真空物理的相关理论,建立了MEMS器件真空封装的数学物理模型,确定了其数值模拟算法。据此,对一封装示例进行了计算,获得了真空回流炉内干燥箱及密封腔体真空度的变化情况,实现了MEMS器件真空封装工艺过程的参数化建模与模拟。     

Modelling and identification of offshore towers with general damping

The modelling problem of offshore towers is considered. A model is proposed which includes viscous and hydrodynamic drag damping and takes into account the stochastic nature of the problem. The model is decoupled into a set of modal equations by using the complex mode theory. A technique is developed to identify the modal parameters and the complex mode shapes by using the noisy excitation and response measurements. This technique is computationally efficient and accurate in the sense of minimizing a criterion function of the estimates variance. A simulation example is presented to demonstrate the results.     

Nonlinear dynamics of MEMS/NEMS resonators: analytical solution by the homotopy analysis method

Microsystem Technologies - Due to various sources of nonlinearities, micro/nano-electro-mechanical-system (MEMS/NEMS) resonators present highly nonlinear behaviors including softening- or...     

Narrow-band filtering by means of triangular meta-material resonators based on RF MEMS cantilevers in CPW configuration

Microsystem Technologies - Triangular resonators, designed by using Radio Frequency Micro Electro Mechanical Systems (RF MEMS) cantilevers in coplanar waveguide (CPW) configuration, have been...     

剪切模量对梁的磁橡胶约束阻尼特性的影响

基于周期耗能相等的原理,将磁橡胶约束阻尼悬臂梁(MRLD)与传统的约束阻尼悬臂梁(CLD)等价,计算MRLD的模态损耗因子,研究了阻尼层剪切模量Gv对MRLD梁阻尼特性的影响.研究表明,在给定激励位移下,当Gv较小时,MRLD与CLD的阻尼一样.增加Gv引起阻尼层滑移,在Gv增加的开始阶段,MRLD表现出比CLD更好的阻尼特性,但进一步提高Gv,MRLD的阻尼性能开始降低并将低于CLD.此外,增加位移激励,使MRLD的阻尼大于CLD阻尼的有效剪切模量Gv的区域向剪切模量小的方向移动;所对应最大阻尼的剪切模量Gvopt也如此.     

基于MEMS的微型飞行器姿态测量系统

利用三轴加速度计和三轴磁强计,设计了基于MEMS技术的微型飞行器姿态测量系统。系统采用C8051F单片机进行各传感器的数据采集,通过串口通信将采集的信息发送到上位机,用四元数解算算法进行数据融合和姿态解算,将俯仰角,横滚角、航向角等信息在上位机界面上显示出来。     

Frequency response of in-plane coupled resonators for investigating the acceleration sensitivity of MEMS tuning fork gyroscopes

The frequency response of in-plane coupled resonators is used for investigating the acceleration sensitivity of a MEMS tuning fork gyroscope (TFG) and a new method of suppressing the acceleration output is presented. The unbalancing of two sense resonators in the TFG caused by fabrication errors converted an external vibration into anti-phase mode excitation. To reduce the acceleration output, decoupling between in- and anti-phase modal frequencies [decoupling ratio (DR)] is crucial, since coupled resonators may cause large anti-phase vibrations from the acceleration. The acceleration output model was verified using two coupled resonators with 1 and 5?% stiffness unbalance. FEM simulation results showed a 25?% reduction in the anti-phase vibration by increasing the decoupling ratio from 0.09 to 0.29, irrespective of the coupled resonators designs. Quantitative analysis of a TFG based on coupled resonators with 1?% stiffness unbalance showed the acceleration output decreased from 5.65 to 1.43?deg/s/g.     

孔结构对水平振动谐振器空气阻尼的比较分析

基于SOI工艺的水平振动梳状硅微谐振器的品质因数Q值在真空封装下能达到105量级以上。但是在常压下,由于受到空气阻尼的影响,其Q值往往降至102量级甚至更小。增加谐振器质量可以提高Q值,但是会增大谐振器面积使绝缘层难以释放。由此提出了一种减小空气阻尼来提高水平振动谐振器Q值的方法,通过设计一系列不同形状的开孔硅微谐振器并比较其实验数据,得到最优的释放孔结构以减小谐振器所受的空气阻尼从而得到更高的Q值。该研究对水平振动谐振器结构设计有一定意义。     

High-fidelity modeling of MEMS resonators. Part I. Anchor loss mechanisms through substrate

A computational model is developed for the prediction of wave propagation in the substrate of a MEMS resonator to study energy loss mechanisms from the vibrating beams to the substrate, viz., anchor loss. The model employs a modified classical Fourier transform method under periodic excitations at the anchor area. The present substrate model, when applied to a typical commercially fabricated substrate, estimates that the anchor loss of an ends-anchored resonator with its center frequency of 50 MHz can reach as high as 0.05% in terms of equivalent damping ratio. Anchor loss versus resonator center frequency is assessed by varying the beam dimension, which predicts that anchor loss increases a hundredfold for every tenfold increase in resonator center frequency in the case of two ends-anchored beam resonators. The substrate model has been integrated into a coupled beam-substrate-electrostatics model and validated with experimental data. Development of the detailed coupled-physics model and its validation is presented in Part II as a companion paper.