A MEMS reconfigurable DGS resonator for K-band applications

A MEMS reconfigurable defected-ground-structure (DGS) resonator using two-dimensional (2-D) periodic DGS for coplanar waveguide (CPW) transmission line and RF MEMS series-resistive switches is proposed. The introduced MEMS reconfigurable DGS resonator has approximately a fixed bandwidth of 8.1 GHz over a wideband frequency range (K-band). The proposed structure can be designed easily for other frequency bands by changing the number of unit-cells of the 2-D PDGS. A cascaded two parallel-resonance circuit model for the MEMS reconfigurable DGS resonator has been introduced as well. The equivalent circuit parameters extraction methods have also been derived. Simulations based on the proposed circuit model are in a very good agreement with the electromagnetic (EM) simulations, which suggests that the MEMS reconfigurable DGS resonator is an inductive controlled reconfigured structure. The structure is designed in CPW environment on a high-resistivity silicon substrate. It is therefore suitable for monolithic integration with standard IC process.     

Free-Form Simulation of Sequential Etching and Surface Characterization for 3-D MEMS Fabrication

A new diffusion-based simulation model of isotropic wet etching and free-form surface characterization method for 3-D free-form microelectromechanical systems (MEMS) fabrication is presented in this paper. To simulate the etching process, a diffusion-based model solved by the finite-element method (FEM) has been developed, allowing extraction of more accurate etch-front data at discrete time steps. In the developed method, free-form MEMS objects are modeled as B-spline functions with material concentration. Finite elements are generated by discretization in the parametric domain of the free-form object and mapping back to the Euclidean space. Points on the etch front are extracted using a Z-map method. The extracted point data are characterized to obtain a B-spline representation of the etch-front surface. Examples from the isotropic etching simulation of 2-D and 3-D objects with both regular and free-form geometry are presented. The developed method allows the simulation of 3-D objects with free-form input and free-form mask opening and facilitates the simulation of sequential etching of free-form objects with irregular mask openings. This paper also discusses applications of the developed method in MEMS process planning that can be realized by taking advantage of the better control of geometry that it provides in MEMS fabrication.     

Influence of developer temperature on the shape of structures fabricated by deep X-ray lithography

This paper describes the fabrication of poly(methyl methacrylate) (PMMA) microstructures with three-dimensional (3-D) sloped sidewalls using synchrotron-radiated (SR) deep X-ray lithography (DXRL). Here, the developer temperature was varied to produce variations in the inclination angle of the sloped sidewalls. We found that the PMMA sidewall inclination angle and height were controlled by the dosage, development time, and development temperature. When the development temperature was low, the inclination angle was nearly 0°, regardless of dosage amounts or exposure time. When the development temperature was high, microstructures with sloped sidewalls were fabricated; as the dosage amount and development time increased, the inclination angle increased. The ability to control the PMMA sidewall inclination angle suggests the application of this technique to microstructure fabrication technologies, such as 3-D microelectromechanical system (MEMS) device components, in which the inclination angle becomes the draft angle for moulding processes.     

Ink-jet printed nanoparticle microelectromechanical systems

Reports a method to additively build three-dimensional (3-D) microelectromechanical systems (MEMS) and electrical circuitry by ink-jet printing nanoparticle metal colloids. Fabricating metallic structures from nanoparticles avoids the extreme processing conditions required for standard lithographic fabrication and molten-metal-droplet deposition. Nanoparticles typically measure 1 to 100 nm in diameter and can be sintered at plastic-compatible temperatures as low as 300°C to form material nearly indistinguishable from the bulk material. Multiple ink-jet print heads mounted to a computer-controlled 3-axis gantry deposit the 10% by weight metal colloid ink layer-by-layer onto a heated substrate to make two-dimensional (2-D) and 3-D structures. We report a high-Q resonant inductive coil, linear and rotary electrostatic-drive motors, and in-plane and vertical electrothermal actuators. The devices, printed in minutes with a 100 μm feature size, were made out of silver and gold material with high conductivity,and feature as many as 400 layers, insulators, 10:1 vertical aspect ratios, and etch-released mechanical structure. These results suggest a route to a desktop or large-area MEMS fabrication system characterized by many layers, low cost, and data-driven fabrication for rapid turn-around time, and represent the first use of ink-jet printing to build active MEMS     

Computer-aided generation of nonlinear reduced-order dynamicmacromodels. I. Non-stress-stiffened case

Reduced-order dynamic macromodels are an effective way to capture device behavior for rapid circuit and system simulation. In this paper, we report the successful implementation of a methodology for automatically generating reduced-order nonlinear dynamic macromodels from three-dimensional (3-D) physical simulations for the conservative-energy-domain behavior of electrostatically actuated microelectromechanical systems (MEMS) devices. These models are created with a syntax that is directly usable in circuit- and system-level simulators for complete MEMS system design. This method has been applied to several examples of electrostatically actuated microstructures: a suspended clamped beam, with and without residual stress, using both symmetric and asymmetric positions of the actuation electrode, and an elastically supported plate with an eccentric electrode and unequal springs, producing tilting when actuated. When compared to 3-D simulations, this method proves to be accurate for non-stress-stiffened motions, displacements for which the gradient of the strain energy due to bending is much larger than the corresponding gradient of the strain energy due to stretching of the neutral surface. In typical MEMS structures, this corresponds to displacements less than the element thickness, At larger displacements, the method must be modified to account for stress stiffening, which is the subject of part two of this paper     

Characterization of contact electromechanics throughcapacitance-voltage measurements and simulations

Electrostatically actuated polysilicon beams fabricated in the multiuser MEMS process (MUMPs) are studied, with an emphasis on the behavior when the beam is in contact with an underlying silicon nitride dielectric layer. Detailed two-dimensional (2-D) electromechanical simulations, including the mechanical effects of stepups, stress-stiffening and contact, as well as the electrical effects of fringing fields and finite beam thickness, are performed. Comparisons are made to quasi-2-D and three-dimensional simulations. Pull-in voltage and capacitance-voltage measurements together with 2-D simulations are used to extract material properties. The electromechanical system is used to monitor charge buildup in the nitride which is modeled by a charge trapping model. Surface effects are included in the simulation using a compressible-contact-surface model. Monte Carlo simulations reveal the limits of simulation accuracy due to the limited resolution of input parameters     

基于窄带水平集的三维平面工艺模拟系统

表面工艺是MEMS制造的一种重要方法,实现其加工过程的计算机仿真可以为相关MEMS工艺研究和器件开发提供技术支持,减少相关MEMS产品的开发成本,缩短其开发周期.基于窄带水平集算法完成了表面加工工艺的三维表面工艺模拟系统.窄带水平集算法稳定,计算速度快处理拓扑变形非常灵活,本文将其应用于该软件仿真系统中,并进行了一列的仿真实验,将仿真结果与实际的流片电镜图对比,验证了仿真系统的精确性.     

Analytical prediction of resonant frequencies of annular stacked dielectric resonator antennas

The method of stacking dielectric resonators for designing multiband and wideband antennas has gained much attention in recent times. However, the existing works lack any theoretical framework for the prediction of resonant frequencies of such stacked structures. In this work, a formal analysis using a cavity model with the mode matching technique is presented to determine all the existing resonant frequencies of annular stacked cylindrical dielectric resonator antennas with and without air gap. The analysis is done separately considering the outermost sidewall of the stack as both perfect magnetic conductor and imperfect magnetic conductor. The theoretical findings are extensively validated against numerous simulations, as well as against a fabricated prototype. It is observed that the perfect magnetic wall condition provides results that are more accurate. The closed‐form equation derived in this work not only helps in accurately predicting the resonant frequencies but also reduces the run‐time manifolds compared to that of the existing trial and error based methods of design using software simulations.     

Tunable magnetic metamaterial based multi-split-ring resonator (MSRR) using MEMS switch components

The split-ring resonator (SRR) arrays are commonly used to form a negative refractive index metamaterial that exhibits an effective negative permeability. However, the region of negative permeability obtained by SRR unit cell is generally limited to a narrow bandwidth at a fixed frequency. In this paper, we present a tunable metamaterial based on multi-split-ring resonators (MSRR) with MEMS switch components to realize controllable magnetic resonant frequency. Numerical simulations are performed to validate the proposed theory and tunability. The simulated results show that the MSRR structure metamaterial can realize digital tuning mode and continuous tuning mode by controlling state and height of MEMS switch components, respectively. Moreover, the simulated results are consistent with the theoretical results, which verify that the proposed theory is effective in prediction and analysis of magnetic resonant frequency. Therefore, such a tunable metamaterial can be reconfigured into a variety of states for use in different applications.     

Modeling of gold microbeams as strain and pressure sensors for characterizing MEMS packages

This work presents the modeling of gold microbeams for characterizing Micro-electro-mechanical systems (MEMS) packages in terms of both strains induced to the MEMS devices and hermetic sealing capability. The proposed test structures are based on arrays of rectangular-shaped clamped-free and clamped–clamped beams, to be realized with a film of electroplated gold by surface micromachining technology. The resonant frequency of the microbeams is modeled by FEM simulations as a function of substrate deformations, which could be induced by the package. Clamped–clamped bridges show a linear change of the square of the resonant frequency in case of in-plane deformations, in fairly good agreement with an approximate analytical model. Cantilever beams are modeled as variable capacitors to detect out-of-plane deformations. Finally, an analytical model to study cantilever beams as resonators for detecting pressure changes is discussed and compared with preliminary experimental results, showing an impact on the quality factor in a range from 10^?2 mbar to 1?bar.     

A new analytical model of single-stage microleverage mechanism in resonant accelerometer

Microleverage mechanism which is widely applied in microelectromechanical systems (MEMS) transfers and amplifies force or displacement from input to output. In this work, one-stage microleverage mechanism is integrated into a biaxial micro resonant accelerometer to improve sensitivity. Force amplification factor of the microleverage is analyzed and deduced by integral method. The results from theoretical model match well with the ones from finite element method (FEM) simulation, which proves that the proposed model is relatively accurate and the width of lever beam is a quite important parameter in design. The resonant accelerometer is successfully fabricated by MEMS technology. Preliminary experiments are conducted and demonstrate differential sensitivity of 71 Hz/g for the accelerometer with resonant frequency of 267.726 kHz.     

Two-Dimensional MEMS Scanner for Dual-Axes Confocal Microscopy

In this paper, we present a novel 2-D microelectromechanical systems (MEMS) scanner that enables dual-axes confocal microscopy. Dual-axes confocal microscopy provides high resolution and long working distance, while also being well suited for miniaturization and integration into endoscopes for in vivo imaging. The gimbaled MEMS scanner is fabricated on a double silicon-on-insulator (SOI) wafer (a silicon wafer bonded on a SOI wafer) and is actuated by self-aligned vertical electrostatic combdrives. Maximum optical deflections of plusmn4.8deg and plusmn5.5deg are achieved in static mode for the outer and inner axes, respectively. Torsional resonant frequencies are at 500 Hz and 2.9 kHz for the outer and inner axes, respectively. The imaging capability of the MEMS scanner is successfully demonstrated in a breadboard setup. Reflectance images with a field of view of are achieved at 8 frames/s. The transverse resolutions are 3.94 mum and 6.68 mum for the horizontal and vertical dimensions, respectively.     

基于切割成型的侧壁表面压阻制作及其参数优化

为了提高MEMS执行器件对面内运动位移（或力学信号）检测的灵敏度并改善侧壁检测电阻制作工艺与其他工艺及其不同器件结构之间的兼容性问题,提出一种基于离子注入工艺和深度反应离子刻蚀（DRIE）工艺相结合制作检测梁侧壁压阻的方法。在此基础上,详细分析了影响位移检测灵敏度和分辨率的各种因素,并对侧壁压阻的结构尺寸及其工艺参数进行优化。最后,给出了侧壁表面压阻在几种不同类型典型MEMS执行器件中的应用,取得了很好的应用效果。     

Characterization of selective polysilicon deposition for MEMS resonator tuning

Variations in micromachining processes cause submicron differences in the size of MEMS devices, which leads to frequency scatter in resonators. A new method of compensating for fabrication process variations is to add material to MEMS structures by the selective deposition of polysilicon. It is performed by electrically heating the MEMS in a 25/spl deg/C silane environment to activate the local decomposition of the gas. On a (1.0/spl times/1.5/spl times/100) /spl mu/m/sup 3/, clamped-clamped, polysilicon beam, at a power dissipation of 2.38 mW (peak temperature of 699/spl deg/C), a new layer of polysilicon (up to 1 /spl mu/m thick) was deposited in 10 min. The deposition rate was three times faster than conventional LPCVD rates for polysilicon. When selective polysilicon deposition (SPD) was applied to the frequency tuning of specially-designed, comb-drive resonators, a correlation was found between the change in resonant frequency and the length of the newly deposited material (the hotspot) on the resonator's suspension beams. A second correlation linked the length of the hotspot to the magnitude of the power fluctuation during the deposition trial. The mechanisms for changing resonant frequency by the SPD process include increasing mass and stiffness and altering residual stress. The effects of localized heating are presented. The experiments and simulations in this work yield guidelines for tuning resonators to a target frequency.     

Multi-modal vibration based MEMS energy harvesters for ultra-low power wireless functional nodes

In this work we discuss a novel design concept of energy harvester (EH), based on Microsystem (MEMS) technology, meant to convert mechanical energy, available in the form of vibrations scattered in the surrounding environment, into electrical energy by means of the piezoelectric conversion principle. The resonant structure, named four-leaf clover (FLC), is circular and based on four petal-like double mass-spring systems, kept suspended through four straight beams anchored to the surrounding Silicon frame. Differently from standard cantilever-type EHs that typically convert energy uniquely in correspondence with the fundamental vibration frequency, this particular shape is aimed to exploit multiple resonant modes and, thereby, to increase the performance and the operation bandwidth of the MEMS device. A preliminary non-optimized design of the FLC is discussed and physical samples of the sole mechanical resonator, fabricated at the DIMES Technology Center (Delft University of Technology, the Netherlands), are experimentally characterized. Their behaviour is compared against simulations performed in ANSYS Workbench?, confirming good accuracy of the predictive method. Furthermore, the electromechanical multiphysical behaviour of the FLC EH is also analysed in Workbench, by adding a layer with piezoelectric conversion properties in the simulation. The measured and simulated data reported in this paper confirm that the MEMS converter exhibits multiple resonant modes in the frequency range below 1 kHz, where most of the environmental vibration energy is scattered, and extracted power levels of 0.2 μW can be achieved as well, in closed-loop conditions. Further developments of this work are expected to fully prove the high-performance of the FLC concept, and are going to be addressed by the authors of this work in the on-going activities.     

Finite element modeling and experimental proof of NEMS-based silicon pillar resonators for nanoparticle mass sensing applications

The potential use of nanoelectromechanical systems (NEMS) created in silicon nanopillars (SiNPLs) is investigated in this work as a new generation of aerosol nanoparticle (NP)-detecting device. The sensor structures are created and simulated using a finite element modeling (FEM) tool of COMSOL Multiphysics 4.3b to study the resonant characteristics and the sensitivity of the SiNPL for femtogram NP mass detection in 3-D structures. The SiNPL arrays use a piezoelectric stack for resonance excitation. To achieve an optimal structure and to investigate the etching effect on the fabricated resonators, SiNPLs with different designs of meshes, sidewall profiles, heights, and diameters are simulated and analyzed. To validate the FEM results, fabricated SiNPLs with a high aspect ratio of approximately 60 are used and characterized in resonant frequency measurements where their results agree well with those simulated by FEM. Furthermore, the deflection of a SiNPL can be enhanced by increasing the applied piezoactuator voltage. By depositing different NPs [i.e., gold (Au), silver (Ag), titanium dioxide (TiO₂), silicon dioxide (SiO₂), and carbon black NPs] on the SiNPLs, the decrease of the resonant frequency is clearly shown confirming their potential to be used as airborne NP mass sensor with femtogram resolution level. A coupling concept of the SiNPL arrays with piezoresistive cantilever resonator in terms of the mass loading effect is also studied concerning the possibility of obtaining electrical readout signal from the resonant sensors.     

Design, damping estimation and experimental characterization of decoupled 3-DoF robust MEMS gyroscope

This paper reports the design implementation of three degree-of-freedom (3-DoF) non-resonant MEMS gyroscope having 2-DoF drive-mode oscillator. The proposed architecture utilizes structurally decoupled active-passive mass configuration to achieve dynamic amplification of oscillation in 2-DoF drive-mode. This results in higher sensitivity and eliminates the need of mode matching for resonance. A low cost standard Metal-Multi User MEMS Processes (MetalMUMPs) is used to fabricate 20 μm thick nickel based gyroscope with an overall reduced size of 2.2 mm × 2.6 mm. The experimental characterization demonstrated that the frequency response of the 2-DoF drive-mode oscillator has two resonant peaks at 754 Hz and 2.170 kHz with a flat operational region of 1.4 kHz between the peaks. The sense-mode resonant frequency lies at 1.868 kHz within this flat operational region where gain is less sensitive to structural parameters and environmental variations. This results in improved robustness to fabrication imperfections and environmental variations and long term stability without utilizing tuning and feedback control. Gyroscope dynamics and system level simulations using behavioral modeling are carried out to predict the performance of the device. Experimental results show close agreement with the behavioral simulation results due to incorporation of improved damping models in behavioral model developed in CoventorWare.     

Architectures for vibration-driven micropower generators

Several forms of vibration-driven MEMS microgenerator are possible and are reported in the literature, with potential application areas including distributed sensing and ubiquitous computing. This paper sets out an analytical basis for their design and comparison, verified against full time-domain simulations. Most reported microgenerators are classified as either velocity-damped resonant generators (VDRGs) or Coulomb-damped resonant generators (CDRGs) and a unified analytical structure is provided for these generator types. Reported generators are shown to have operated at well below achievable power densities and design guides are given for optimising future devices. The paper also describes a new class-the Coulomb-force parametric generator (CFPG)-which does not operate in a resonant manner. For all three generators, expressions and graphs are provided showing the dependence of output power on key operating parameters. The optimization also considers physical generator constraints such as voltage limitation or maximum or minimum damping ratios. The sensitivity of each generator architecture to the source vibration frequency is analyzed and this shows that the CFPG can be better suited than the resonant generators to applications where the source frequency is likely to vary. It is demonstrated that mechanical resonance is particularly useful when the vibration source amplitude is small compared to the allowable mass-to-frame displacement. The CDRG and the VDRG generate the same power at resonance but give better performance below and above resonance respectively. Both resonant generator types are unable to operate when the allowable mass frame displacement is small compared to the vibration source amplitude, as is likely to be the case in some MEMS applications. The CFPG is, therefore, required for such applications.     

A parametrized three-dimensional model for MEMS thermal shear-stress sensors

This paper presents an accurate and efficient model of MEMS thermal shear-stress sensors featuring a thin-film hotwire on a vacuum-isolated dielectric diaphragm. We consider three-dimensional (3-D) heat transfer in sensors operating in constant-temperature mode, and describe sensor response with a functional relationship between dimensionless forms of hotwire power and shear stress. This relationship is parametrized by the diaphragm aspect ratio and two additional dimensionless parameters that represent heat conduction in the hotwire and diaphragm. Closed-form correlations are obtained to represent this relationship, yielding a MEMS sensor model that is highly efficient while retaining the accuracy of three-dimensional heat transfer analysis. The model is compared with experimental data, and the agreement in the total and net hotwire power, the latter being a small second-order quantity induced by the applied shear stress, is respectively within 0.5% and 11% when uncertainties in sensor geometry and material properties are taken into account. The model is then used to elucidate thermal boundary layer characteristics for MEMS sensors, and in particular, quantitatively show that the relatively thick thermal boundary layer renders classical shear-stress sensor theory invalid for MEMS sensors operating in air. The model is also used to systematically study the effects of geometry and material properties on MEMS sensor behavior, yielding insights useful as practical design guidelines.     

Optimal design of ITO/organic photonic crystals in polymer light-emitting diodes with sidewall reflectors for high efficiency

This study aims to achieve large extraction of light emission from polymer light emitting diodes (PLEDs) via optimizing photonic crystals (PCs) and sidewall angle reflectors. Both PCs and sidewall reflectors can be resulting in increasing light emission in useful directions and reducing refection loss. The optimization is achieved through the optical modeling using a 3D finite-difference time-domain (FDTD) method and the intelligent numerical optimization technique, genetic algorithm (GA). The optimal design of PCs and sidewall angle reflectors are presented in details. To accurately predict light extraction of the PLED, the numerical simulation tool, the FDTD method is employed. Based on the FDTD simulation, the optimal sidewall angle which can increase maximum light extraction efficiency (LEE) in our designed PLED structure is 35°. With the optical modeling of optimal sidewall angle reflectors via FDTD computation and the next step is using GA optimization to seek optimal pitch and radius of photonic crystals. According to the GA optimal result, the ratio of pitch to wavelength is 0.47 times and the ratio of radius to pitch is 0.25 times. GA is a powerful tool to cope with a complicated optimization problem with multiple variables to optimize. The PLEDs with optimized PCs and angle of sidewall reflectors would increase extraction of light emission from 20 to 26?% and the 3D FDTD calculation was conducted to explain this result.