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.     

Comparative numerical study of FEM methods solving gas damping in perforated MEMS devices

Three different numerical strategies are presented for the estimation of the damping force acting on perforated movable MEMS dampers. Results from the 2D Perforated Profile Reynolds (PPR) method and the simplified 2D ANSYS method are compared with accurate full 3D flow simulations. Altogether, 32 different topologies are compared varying, e.g., the dimensions of the square damper and the square holes, and the number of holes. The case of uniform perforation and perpendicular motion is studied. Oscillation in the low frequency regime is assumed, that is, the compressibility and inertia of the gas are ignored in the study. While the PPR method is in good agreement with the 3D simulations, the forces given by the ANSYS method were considerably smaller. The reasons for this are studied, and a compact expression to explain the small forces is derived.     

The effect of nonlinear elasticity on the large amplitude free vibration behavior of elastic plates at small scale

The effect of nonlinear elasticity on the free vibration behavior of elastic plates has been evaluated by employing continuum mechanics model. The second-order non-linear stress–strain relationship has been considered and the Kirchhoff’s hypothesis has been applied on the elastic plate. The large deformation during vibration has also been considered. By using the Hamilton principle, the governing equations of the free vibration of the plate under different boundary condition have been obtained. In order to get the explicit solutions of the governing equations, the Galerkin’s method and the harmonic balance method have been utilized. The relationship between the vibration frequency and the vibration amplitude has been discussed and the vibration frequencies of different shaped plate have been compared. It is perceived that the nonlinear elasticity has a distinct effect on the free vibration of the plate.

     

Electromagnetic MEMS microspeaker for portable electronic devices

This work presents the conception, the microfabrication, and the electroacoustic characterization of a new electromagnetic microspeaker based on silicon. The objectives are to get improved sound quality compared to that of conventional microspeakers, while keeping the electroacoustic efficiency as high as possible. An optimized stiffening silicon microstructure let the sound radiator be extremely light and rigid. The mobile part is suspended to the fixed part by silicon suspension springs, which enable large out-of-plane displacement. The acoustic radiator is actuated by an electromagnetic motor, composed of a fixed permanent magnet and a planar coil located on top of the silicon radiator. The piston-like motion of the radiator favored by this structure is very beneficial for the sound quality. Electro–mechano–acoustic characterization of the microfabricated microspeaker showed that the radiator surface could run out-of-plane with displacements higher than ±400 μm, with no mechanical and electrical failure. For an electrical power of 0.5 W, the microspeaker was capable to generate a sound pressure level of 80 dB at 10 cm, from 330 Hz up to 20 kHz frequency. The efficiency reaches 3 × 10^?5, that is to say three times more than typical efficiency of conventional microspeakers. Moreover, as characterization results showed, the existence of very few structural modes and the low electroacoustic distortions evidence the high sound quality of the microspeaker.     

Solid-based CAPP for surface micromachined MEMS devices

Process planning for a MEMS device is almost always conducted manually by the designer to date. As the structures of MEMS devices become more and more complicated, in order to release the designers from the hard and tedious work and speed up the development of MEMS products, such a situation should be changed. In this study, a solid based CAPP method for surface micromachined MEMS device is presented. With this method, a MEMS device is designed with a traditional CAD system, and its process planning is conducted automatically based on the solid model created. The process features with engineering semantics are extracted first. Then, the process layer model is constructed with each process layer of the model being coincident with the fabrication layer of surface micromachining. Finally, the masks are synthesized and the fabrication process is generated. Furthermore, to guarantee the manufacturability of the designed MEMS device, a systematic evaluation method is proposed. The proposed design and CAPP methods enable designers to concentrate on functional and shape design of MEMS devices.     

Low-noise MEMS vibration sensor for geophysical applications

The need exists for high-sensitivity, low-noise vibration sensors for various applications, such as geophysical data collection, tracking vehicles, intrusion detectors, and underwater pressure gradient detection. In general, these sensors differ from classical accelerometers in that they require no direct current response, but must have a very low noise floor over a required bandwidth. Theory indicates a capacitive micromachined silicon vibration sensor can have a noise floor on the order of 100 ng/√Hz over 1 kHz bandwidth, while reducing size and weight tenfold compared to existing magnetic geophones. With early prototypes, we have demonstrated Brownian-limited noise floor at 1.0 μg/Hz, orders of magnitude more sensitive than surface micromachined devices such as the industry standard ADXL05     

MEMS压电阵列振动能量收集器

近年来,随着微能源的发展,微型压电振动能量收集器得到了广泛关注,但传统d31模式PZT薄膜微型压电振动能量收集器输出电压普遍较低,难以满足应用需求。为提高微型压电振动能量收集器的输出电压,论文提出了共质量块悬臂梁阵列压电振动能量收集器新结构,该结构包含压电悬臂梁单元组成的阵列和一个质量块,悬臂梁阵列共用质量块。采用有限元方法对该结构进行了优化设计,得到压电悬臂梁单元优化尺寸为3 mm×2.4 mm×0.05 mm,硅质量块优化尺寸为8 mm×12.4mm×0.5 mm。设计了MEMS压电阵列振动能量收集器加工工艺流程,加工出原理样件。在1 gn加速度,239.7 Hz谐振频率激励下,测试得到样件输出开路电压有效值为9.16 V;在最优化负载200 kΩ下,负载输出电压有效值为5.51 V,输出功率为151.8μW。     

MEMS光敏BCB硅—硅键合工艺研究

光敏BCB作为粘结介质进行键合工艺实验研究。实验中选用XUS35078负性光敏BCB,提出了优化的光刻工艺参数,得到了所需要的BCB图形层,然后将两硅片在特定的温度与压力条件下完成了BCB键合。测试表明:该光敏BCB具有较小的流动性和较低的塌陷率。键合后的BCB胶厚约为11.6μm,剪切强度为18MPa,He细检漏率小于5.0×10-8atm·cm3/s。此键合工艺可应用于制作需要低温工艺且不能承受高电压的MEMS器件。     

Single mask fabrication process for movable MEMS devices

The current work reports on the realization of movable micromachining devices using self-aligned single-mask fabrication process. Only dry etching process utilizing inductively coupled plasma reactive ion etching was used to release 3D micro structures from single crystal silicon substrate. No wet etching process is required to release the structures as is the case with silicon on insulator (SOI) wafers. Also the developed process does not require an SOI substrate and accordingly dispensing with the application of a wet etching step, thus yielding uniform structures without stiction. The optimized process was applied to realize thermally actuated microgrippers. The article presents the development of the fabrication process and demonstrates the operation of the fabricated device. The optimized process provides an avenue for low cost fabrication of movable micromachining devices without the use of complicated wet etching steps typically associated with SOI substrates.     

Uncertainty quantification of MEMS devices with correlated random parameters

The concern about process deviations rises because that the performance uncertainty they cause are strengthened with the miniaturization and complication of Microelectromechanical System (MEMS) devices. To predict the statistic behavior of devices, Monte Carlo method is widely used, but it is limited by the low efficiency. The recently emerged generalized polynomial chaos expansion method, though highly efficient, cannot solve uncertainty quantification problems with correlated deviations, which is common in MEMS applications. In this paper, a Gaussian mixture model (GMM) and Nataf transformation based polynomial chaos method is proposed. The distribution of correlated process deviations is estimated using GMM, and modified Nataf transformation is applied to convert the correlated random vectors of GMM into mutually independent ones. Then polynomial chaos expansion and stochastic collection can be implemented. The effectiveness of our proposed method is demonstrated by the simulation results of V-beam thermal actuator, and its computation speed is faster compared with the Monte Carlo technique without loss of accuracy. This method can be served as an efficient analysis technique for MEMS devices which are sensitive to correlated process deviations.

     

A new analytical model for switching time of a perforated MEMS switch

In this paper, the design of a low-k meander based MEMS shunt capacitive switch with perforated beam meander has been presented. A closed form analytical model to calculate the switching time of designed structure is proposed. The model is based on modified Mejis and Fokkema’s capacitance model and linearization of non-linear electrostatic force on the switch beam. The model is utilized in evaluating the switching time for uniform as well as non-uniform serpentine meander designs, considering different values of actuation voltage and a wide variation of switching parameters. This work takes into account the beam perforation, fringing field and stiffness effect simultaneously altogether. The results obtained for both the meander designs under every design specifications has been found out to be less than or approximately equal to 100 µs. These model based results are then compared with 3D FEM simulated values. Comparative Analysis indicated that the model results and simulation results are in close agreement with each other.

     

A new Tapered-L shaped springs based MEMS piezoelectric vibration energy harvester designed for small rolling bearing fault detection

Microsystem Technologies - This paper examines the simulation-based performances of piezoelectric MEMS vibration energy harvester made up of two Tapered-L shaped springs and one seismic mass, which...     

Large amplitude vibrations of circular plates with mixed boundary conditions

In this paper, a method of analysing large amplitude vibrations of circular plates with mixed boundary conditions is explained and is illustrated with an example where part of the boundary is clamped and the remaining simply-supported     

Practice and carryover effects when using small interaction devices

The use of interaction devices in modern work often challenges the human motor system, especially when these devices introduce unfamiliar transformations to the user. In this paper we evaluated expert performance and skill differences between experts and novices when using small motion- and force-controlled interaction devices (touchpad and mini-joystick) in an applied text-editing task. Firstly, experts performed better with their familiar input device than with an unfamiliar one. Particularly touchpad experts operating the unfamiliar mini-joystick showed highly asymmetric carryover costs. Results showed that the efficient performance of experts depended on domain-specific skills, which were not transferable. Secondly, with considerable practice (more than observed for simple and short tasks) novices were brought up to higher levels of performance. The motion-transformation between hand and cursor action was easier in understanding and application than the force-transformation. Thus, the touchpad was used more efficiently than the mini-joystick. In conclusion, practice effects found so far are considerably underestimated when it comes to an applied task. The results give reason to develop and implement skill-sensitive training procedures, since the acquisition of domain-specific skills is critical for expert performance. As a consequence, training procedures might be essential for complex applications and/or unfamiliar device transformations.     

减小临界振幅的机理与试验研究

对于受迫振动系统，当激励频率增加并且通过共振(临界)频率时，系统的振幅将达到其峰值．通过相位调制可以有效地减小共振振幅，其机理是振幅的变化取决于相应和激励之间的相位差，而此相位差可以通过控制激励频率的变化规律进行调制．该方法由受变频率脉冲激励的悬臂梁进行了实验验证．实验结果表明，对于给定的最大频率增加速率，通过相位调制可以将共振振幅减小18％左右．     

Damage and failure in silicon-glass-metal microfluidic joints for high-pressure MEMS devices

The design, fabrication, and testing of microfluidic joints consisting of Kovar metal tubes attached to silicon using borosilicate glass for high pressure microelectromechanical systems devices are presented. The MIT microrocket, which requires microfluidic joints to sustain pressures of at least 12.7 MPa and temperatures in excess of 700 K, is used to demonstrate the feasibility of the glass sealing methodology. A key concern in such joints is the occurrence of cracks due to residual stresses during fabrication, which can affect the load-carrying capability. To obtain a better understanding of the damage and failure characteristics, a hierarchical approach was taken. First, two types of joint configurations with several glass compositions and geometries were considered at the joint-level. Axial tension and pressure tests were performed, and finite element models were used to obtain the residual stress field and to predict failure loads based on linear elastic fracture mechanics. Subsequently, tests were performed on actual and dummy microrockets to validate the methodology at the device-level. Key observations include the importance of bonding between the Kovar tube and the silicon sidewall, which can help increase joint strength, and the detrimental effects of joint proximity under differential pressure loading and manufacturing defects in multiple joint specimens. In addition to specific experimental and analyses results that allow a physical understanding of the damage and failure mechanisms, another key contribution of this work is the overall insight of the design and analysis of reliable glass-sealed microfluidic packages. This insight will help one make better design and process selections for packages in other high-pressure silicon-based MEMS applications.     

Elastoplastic analysis of thick perforated plates with application to prestressing anchor heads

The elastoplastic finite element stress analysis of a prestressing anchor head is described. The anchor head constitutes part of an unbonded tendon system for a prestressed concrete nuclear reactor vessel. The anchor head, which is a thick plate with a central region perforated by a large number of holes, is analyzed using an equivalent homogeneous material with numerically determined effective elastic constants and yield stress. Maximum inelastic tensile strains are calculated as a function of anchor head load level, and related to observed failure modes.     

振动环境下MEMS加速度计的可靠性评估

在MEMS加速度计加速寿命试验及加速性能退化试验研究的基础上,对MEMS加速度计在振动环境下的可靠性技术进行了研究.通过理论分析MEMS加速度计在振动环境下的失效模式和失效机理,结合具体的试验条件设计了加速度计加速寿命试验及加速性能退化试验方案,并对MEMS加速度计在振动环境下的失效数据分别进行了加速寿命可靠性评估及加速性能退化可靠性评估.研究表明,两种评估方法得到的评估结果基本一致;加速性能退化评估方法适用于MEMS加速度计在振动环境中的可靠性研究,且该方法简捷、正确可行、节省试验费用,为MEMS加速度计在实际应用中提供了重要的参考依据.