Microelectromechanical Systems Research Articles

Fatigue-Induced Failure of Polysilicon MEMS: Nonlinear Reduced-Order Modeling and Geometry Optimization of On-Chip Testing Device

In the case of repeated loadings, the reliability of inertial microelectromechanical systems (MEMS) can be linked to failure processes occurring within the movable structure or at the anchors. In this work, possible debonding mechanisms taking place at the interface between the polycrystalline silicon film constituting the movable part of the device and the silicon dioxide at the anchor points are considered. In dealing with cyclic loadings possibly inducing fatigue failure, a strategy is proposed to optimize the geometry of an on-chip testing device designed to characterize the strength of the aforementioned interface. Dynamic analyses are carried out to assess the deformation mode of the device and maximize the stress field leading to interface debonding. To cope with the computational costs of numerical simulations within the structural optimization framework, a reduced-order modeling procedure for nonlinear systems is discussed, based on the direct parametrization of invariant manifolds (DPIM). The results are reported in terms of maximum stress intensification for varying geometry of the testing device and actuation frequency to demonstrate the accuracy and computational efficiency of the proposed methodology.

In–situ strain control in epitaxial silicon carbide compound semiconductor

Residual strain in an epilayer grown on a foreign wafer induces epiwafer’s bow, that is often considered undesirable. Wafer bow however, can be advantageous because both the direction and magnitude of strain are vital for the fabrication of various Micro Electro Mechanical Systems (MEMS), such as resonators. Here strain control is reported for highly mismatched heteroepitaxy of cubic silicon carbide (3C–SiC) compound semiconductor on silicon (Si), a prized functional material, dependent solely on carbon to silicon ratio (C/Si) during growth. While Si–rich condition enhances growth and generates positive curvature i.e. tensile strain, C–rich condition suppresses growth and produces negative curvature i.e. compressive strain. An optimum region emerges with virtually no strain and superior crystallinity. Our findings are significant for the knowledge of heteroepitaxy of 3C–SiC and may be broadened to heteroepitaxy of other compound semiconductors.

Wavelength optimization of fine optical surface defect detection based on FDTD

Due to the similar order of magnitude of the defect size and the detection wavelength, when detecting micro-/nano-scale defects on the surface of a fine optical component, the intense modulation of the optical field poses challenges in correlating imaging widths of defects with actual widths. A dark-field scattering imaging (DFSI) model, based on the finite difference time domain (FDTD) method, is established to study the imaging for triangular and circular section defects and investigate the influence of wavelength on defect width detection. Simulated results indicate that a shorter wavelength of the light source in a DFSI detection system leads to a larger mapping range between the imaging width and the actual defect width, which makes calibration less difficult. A DFSI detection system for micro-/nano-scale surface defects on optical components is built to test defects with rectangular cross-sections on a calibration board. The defect widths estimated from the experimental and simulated results are in good agreement, with a root-mean-square error (RMSE) of 0.11 µm.

Characterization of the ion angle distribution function in low-pressure plasmas using a micro-electromechanical system

In recent years, micro-electromechanical systems (MEMSs) have found broad applications in various sensors. However, aside from quartz crystal microbalances, they have not yet been utilized in plasma analysis. Building on previous work with piezoelectric MEMS, the functionality of a MEMS-based sensor system capable of measuring the ion angular distribution function on the wafer holder surface is demonstrated. To enable this functionality, an array of high aspect ratio holes was added to the tiltable silicon plate of a piezoelectric MEMS. These holes allow for the filtering of incoming ions based on their angle perpendicular to the surface of the tiltable element. An algorithm was developed to fit the width and mean of the ion angular distribution function (IADF) based on the RMS ion current for various MEMS amplitudes. Compared to previously used methods for measuring the IADF, the MEMS presented in this paper represents a significant miniaturization. This work is the first to successfully characterize the angular distribution function of ions using a MEMS.

An On-Chip Second-Order Elastic Topological Insulator for Demultiplexing Out-of-Plane and In-Plane Corner Modes.

Second-order elastic topological insulators (SETIs) with tightly localized corner states present a promising avenue for manipulating elastic waves in lower dimensions. However, existing SETIs typically support corner states of only a single mode, either out-of-plane or in-plane. In this work, an on-chip SETI that simultaneously hosts both high-frequency out-of-plane and in-plane corner states at ≈0.2MHz is introduced. The presence of these corner states is experimentally validated, and their selective excitation by tuning the excitation frequency is demonstrated. This capability to demultiplex out-of-plane and in-plane corner states positions the SETI as a potential platform for developing multifunctional elastic devices and enhancing the communication capacities of elastic waves. Furthermore, due to its structural simplicity, the SETI can be readily scaled and integrated into on-chip elastic circuits, making it suitable for applications in micro-electromechanical systems.

Microfluidics in Cardiac Microphysiological Systems: A review

Abstract Inspired by the advances in microfabrication of microelectromechanical systems (MEMS), microphysiological systems (MPS) capitalized on the fabrication techniques of MEMS technology and pivoted to biomedical applications with select biomaterials and design principles. With the new initiative to refute animal testing and develop valid and reliable alternatives, MPS platforms are in greater demand than ever. This paper will first present the major types of microphysiological systems in the cardiovascular research space, and then review the core design principles of such systems to closely replicate the in vivo physiology. Fabrication methodologies of the platform, as well as technologies that enable patterning and functionalizing scaffolds, and the various sensing modalities that can interface with such MPS platforms, are reviewed and discussed. This review aims to provide a comprehensive picture of cardiac microphysiological systems in which microfluidics play an important role in the design, fabrication, and sensing modalities, and prospects of how this platform can continue to drive further improvements in cardiovascular research and medicine.

Study on the Application of Vibration Energy Harvester Based on 3D Chip-scale Solenoids Coil in Rail Transit

Introduction: A 3D chip-scale solenoid coil was fabricated by micro-electro-mechanical system (MEMS) and wafer-level micro casting technology, and an electromagnetic vibration energy harvester was manufactured with an NdFeB permanent magnet. Methods: Three coils with different turns were designed, namely 45 turns, 90 turns, and 150 turns. The coils had a wire width of 40 microns, a pitch of 25 microns, and a thickness of 150 microns. The permanent magnet was cylindrical with a diameter of 1.8 mm. According to the length of the coil, three specifications of 3/6/10 mm were selected for the permanent magnet. Special PCB circuit testing tooling was processed to test the actual performance of three kinds of permanent magnet energy harvesters with different specifications. Results: The vibration frequency was set to 10 Hz~150 Hz, and the acceleration was designed to be 50 m/s2~300 m/s2. For the energy harvester with 90 turns, a maximum output power of 75 μW was obtained under vibration conditions of 100 m/s2 & 30 Hz. The experimental data showed that vibration frequency, acceleration, and sample size had a certain influence on the energy conversion and output power of vibration. Conclusion: Through the above study, the design and performance of vibration power generation devices can be optimized better to match the actual application requirements of rail transit.

Opportunities and challenges involving repulsive Casimir forces in nanotechnology

The Casimir force, which arises from quantum electrodynamic fluctuations, manifests as an attraction between metallic surfaces spaced mere hundreds of nanometers apart. As contemporary device architectures scale down to the nano- and microscales, quantum phenomena exert increasing influence on their behaviors. Nano- and microelectromechanical systems frequently encounter issues such as components adhering or collapsing due to the typically attractive Casimir interactions. Consequently, significant efforts have been devoted to manipulating Casimir forces, aiming to transition them from attractive to repulsive. This ability holds promise for mitigating component collapse in nanodevices and facilitating the realization of quantum levitation and ultralow friction devices. Four primary strategies have been proposed for engineering repulsive Casimir forces: employing liquid media, magnetic materials, thermodynamic nonequilibrium conditions, and specialized geometries. In this review, we examine these approaches for engineering repulsive Casimir forces, analyzing their experimental feasibility, and discussing potential implementations.

A first-principles calculations investigate the superlubricity and adhesion performance of structural superlubricity micro-components on polydimethylsiloxane surface

Adhesion and friction are crucial considerations in the design of microelectromechanical systems because they can directly influence the energy, dissipation and wear of the system. Current related studies are primarily conducted between graphite and hard materials, such as graphite, mica and gold, but lack the theoretical support of superlubricity on the surfaces of related flexible substrates, such as Polydimethylsiloxane (PDMS). Consequently, friction and wear at the flexible interface represent a significant challenge in the failure of microelectromechanical systems devices. In this paper, we use density functional theory to simulate the adhesion characteristics and friction behaviour of structural superlubricity micro-components on the surface of a flexible substrate in an atmospheric environment. The lower graphene layer of the structural superlubricity micro-components exhibits superior adhesion performance with the PDMS substrate. The increase in normal load is simulated by changing the spacing of layers. The interlayer bonding energy increases with increasing load. The transverse friction increases gradually with the increase in load, while the average friction coefficient decreases. Graphene can reach the superlubricity state on the PDMS substrate. The reliability of this phenomenon is verified by electrical performance. We also investigate the effect of tensile strain on the friction behaviour and electrical properties. These calculations should be combined with analysis of the mechanical properties to verify the reliability of the friction performance.

Microelectromechanical System Resonant Devices: A Guide for Design, Modeling and Testing

Microelectromechanical systems (MEMSs) are attracting increasing interest from the scientific community for the large variety of possible applications and for the continuous request from the market to improve performances, while keeping small dimensions and reduced costs. To be able to simulate a priori and in real time the dynamic response of resonant devices is then crucial to guide the mechanical design and to support the MEMSs industry. In this work, we propose a simplified modeling procedure able to reproduce the nonlinear dynamics of MEMS resonant devices of arbitrary geometry. We validate it through the fabrication and testing of a cantilever beam resonator functioning in the nonlinear regime and we employ it to design a ring resonator working in the linear regime. Despite the uncertainties of a fabrication process available in the university facility, we demonstrate the predictability of the model and the effectiveness of the proposed design procedure. The satisfactory agreement between numerical predictions and experimental data proves indeed the proposed a priori design tool based on reduced-order numerical models and opens the way to its practical applications in the MEMS industry.

The Role of Micro Propulsion in Enabling Autonomous Operations of Nanosatellites

Micro-Electro-Mechanical Systems (MEMS)-based propulsion devices have significant potential for providing high specific power. The application of Micro Power Generation technology to space propulsion systems can enhance orbit and station-keeping capabilities, potentially at lower costs. New-generation spacecraft and satellites are becoming smaller and require micro-propulsion systems for all aspects of their operations. The development of micro-propulsion systems with associated combustors for micro-electricity generation, utilizing liquid fuel, presents major challenges in fuel injection, mixing, combustion, and chemical reactor systems. A micro-spacecraft with high-accuracy station-keeping and attitude control capabilities needs to have low mass and deliver small impulses. Each nanosatellite will weigh a maximum of 10 kg, including the propellant mass. Provisions for orbital manoeuvres, attitude control, multiple sensors, and instruments, along with full autonomy, will result in a highly capable miniaturized satellite. All onboard electronics will endure a total radiation dose of 100 k rads over a two-year mission lifetime. Nanosatellites designed for in-situ measurements will be spin-stabilized and equipped with a complement of particles and fields instruments. Nanosatellites intended for remote measurements will be three-axis stabilized and equipped with imaging and radio wave instruments. Key technologies under development include: advanced, miniaturized chemical propulsion systems; miniaturized sensors; highly integrated, compact electronics; autonomous onboard and ground operations; miniaturized onboard orbit determination methods; onboard RF communications capable of transmitting data to Earth from significant distances; lightweight and efficient solar array panels; lightweight, high-output battery cells; a miniaturized heat transport system; lightweight yet strong composite materials for nano-satellite and deployer-ship structures; and simple, reusable ground systems.

Effects of sputtering process and annealing on the microstructure, crystallization orientation and piezoelectric properties of ZnO films

Ceramic piezoelectric films play a crucial role in sensors, acoustic wave devices, and micro-electromechanical systems (MEMS) due to their superior piezoelectric properties. This study focuses on optimizing ZnO piezoelectric films through radio frequency (RF) magnetron sputtering under a combination of varied deposition parameters such as tuning the target-substrate distance, sputtering power, and pressure effectively to control the atomic bombardment, collisions, and surface diffusion of sputtered particles, thereby influencing the surface morphology, grain size, thickness and chemical composition of the ZnO films. Furthermore, annealing heat treatment enhances the crystallization quality and piezoelectric properties of the ZnO films. Results show that annealing the films sputtered at a magnetron power of 50 W at 300 °C maximizes a favorable c-axis (002) orientation. Piezoelectric performance confirms that the annealed ZnO films exhibits enhanced piezoelectric amplitude, mechanical-electrical signal response, stable linear piezoelectric behavior, and a 180° phase flip under voltage excitation. This work is promising to lay a foundational solution for the development of advanced sensors with excellent piezoelectric properties.

Investigations into Capillary Forces and Capillary Rise in a Three-Finger Microgripper and a Plate: Numerical Simulations and Experimental Validation

The assembly and position adjustment of micro-components have wide applications in micro-electromechanical systems, wafer packaging and biomedicine. However, current single-finger microgrippers only allow for the pickup and release of micro-components. In the present study, a three-finger capillary microgripper was developed to pick up, release and adjust the position of micro-components. The capillary force and the capillary rise generated by the capillary bridge were investigated by simulation and experiments. A simulation model was set up by the minimum energy method. On the established experimental platform, capillary forces were measured at different separation distances. When the volume was 0.9 μL, the maximum capillary forces gained from the capillary bridge model and experiments were 95.2 μN and 96.0 μN, respectively. A comparison of the capillary bridge models and the experimental results of the capillary forces demonstrate the reliability of the capillary bridge models. The influences of various parameters were investigated in detail by the capillary bridge model. The results demonstrate that when the side of the probe is hydrophilic, the variations in the capillary force with various factors such as separation distance and capillary bridge volume is non-monotonic, which is caused by the restriction of the probe edge.

Nonvolatile silicon photonic MEMS switch based on centrally clamped stepped bistable mechanical beams

High-performance photonic switches are essential for large-scale optical routing for AI large models and the Internet of Things. Realizing nonvolatility can further reduce power consumption and expand application scenarios. We propose a nonvolatile 2×2 silicon photonic micro-electromechanical system (MEMS) switch compatible with standard silicon photonic foundry processes. The switch employs an electrostatic comb actuator to change the air gap of the compact horizontal adiabatic coupler and achieves nonvolatility with centrally clamped stepped bistable mechanical beams. The photonic switch features a 10s μs-scale switching speed and a 10s fJ-scale simulated switching energy within a 100 μm×100 μm footprint, with ≤12 V driving voltages. This 2×2 switch can be used in a variety of topologies for large-scale photonic switches, and its nonvolatility can potentially support future photonic field programmable gate array designs.

Application of liquid metal driven-abrasive flow to material removal for the inner surface of channel

Gallium-based eutectic liquid metal alloys possess unique properties such as deformability, high electrical conductivity, and low vapor pressure. These characteristics have generated significant interest in their application for stretchable electronics and microelectromechanical systems (MEMS). Precise manipulation of liquid metal within electrolytes is essential to meet specific functional requirements. This study investigates the electrostatic manipulation of liquid metal in an alkaline solution with abrasives for material removal from the inner surfaces of flow channels. The polarization of the double layer at the gallium‑indium alloy and electrolyte interface is analyzed, elucidating the principle of electrolyte propulsion via continuous electrowetting. A theoretical model is developed, and two- and three-dimensional transient and steady-state simulations of the liquid metal-driven abrasive flow are conducted. Results demonstrate that this method effectively removes material from the inner walls of straight channels during cyclic motion. Utilizing continuous electrowetting, an experimental apparatus was designed, where gallium‑indium liquid metal propelled silicon carbide abrasives against PMMA channel walls. Experimental results showed effective material removal, consistent with finite element simulations, confirming the feasibility of this innovative approach.

MEMS-metasurface-enabled mode-switchable vortex lasers.

Compared to conventional lasers limited to generating static modes, mode-switchable lasers equipped with adjustable optics significantly enhance the flexibility and versatility of coherent light sources. However, most current approaches to achieving mode-switchable lasers depend on conventional, i.e., inherently bulky and slow, optical components. Here, we demonstrate fiber lasers empowered by electrically actuated intracavity microelectromechanical system (MEMS)-based optical metasurface (MEMS-OMS) enabling mode switching between fundamental Gaussian and vortex modes at ~1030 nm. By finely adjusting the voltage applied to the MEMS mirror, high-contrast switching between Gaussian (l = 0) and vortex (l = 1, 2, 3, and 5, depending on the OMS arrangement) laser modes is achieved, featuring high mode purities (>95%) and fast responses (~100 microseconds). The proposed intracavity MEMS-OMS-enabled laser configuration provides an at-source solution for generating high-purity fast-switchable laser modes, with potential applications ranging from advanced optical imaging to optical tweezers, optical machining, and intelligent photonics.

Aspect ratio-dependent etching in silicon using XeF2: experimental investigation and comparative analysis with dry etching methods

Abstract Silicon machining plays a crucial role in shaping three-dimensional structures for Micro-Electro-Mechanical Systems (MEMS) applications. This study investigates Aspect Ratio Dependent Etching (ARDE) across various silicon etching processes, with a particular focus on Xenon Difluoride (XeF2) etching, in comparison to Reactive Ion Etching (RIE) and Deep Reactive Ion Etching (DRIE).By exploring different etching parameters, the study highlights the presence of ARDE in both plasma and non-plasma etching processes. Additionally, it is demonstrated that ARDE can be modeled by a saturating exponential function through experimental adjustment of parameters, enabling the prediction of etching profiles.

A novel pendulum-like deformation-limited piezoelectric vibration energy harvester triggered indirectly via a smoothly plucked drive plate

Vibration energy harvesting using the piezoelectric effect is emerging as a promising sustainable energy solution for micro-electromechanical systems and wireless sensor networks. Nevertheless, the advancement of piezoelectric vibration energy harvesters has been hindered by reliability issues stemming from piezoelectric material damage due to excessive deformation. To address this challenge, a pendulum-like deformation-limited piezoelectric vibration energy harvester triggered indirectly via a smoothly plucked drive plate (D-LPVEH) is proposed. The D-LPVEH effectively constrains the maximum deformation of the piezoelectric beam, enabling unidirectional deformation and enhancing reliability even under unexpected impacts, by introducing a drive plate. Simulation and experimental findings both validate the efficacy of limiting the piezoelectric beam’s deformation by integrating the drive plate structure. Besides, the D-LPVEH has a good environmental adaptability and designability, which means D-LPVEH can work in different frequency ranges by adjusting proof mass and mass arm length, even at low frequency environmental vibrations of a few Hertz. Moreover, the D-LPVEH demonstrates a peak output power of 0.77 mW at a mere 5.6 Hz, with an optimal load resistance of 100 kΩ, and can consecutively illuminate a minimum of 100 commercial blue LEDs. The D-LPVEH has demonstrated to have good power generation and high reliability. This design will provide a reference for the research on improving the reliability of PVEH.

Integrating Multiple Hierarchical Parameters to Achieve the Self-Compensation of Scale Factor in a Micro-Electromechanical System Gyroscope.

The scale factor of thermal sensitivity serves as a crucial performance metric for micro-electromechanical system (MEMS) gyroscopes, and is commonly employed to assess the temperature stability of inertial sensors. To improve the temperature stability of the scale factor of MEMS gyroscopes, a self-compensation method is proposed. This is achieved by integrating the primary and secondary relevant parameters of the scale factor using the partial least squares regression (PLSR) algorithm. In this paper, a scale factor prediction model is presented. The model indicates that the resonant frequency and demodulation phase angle are the primary correlation terms of the scale factor, while the drive control voltage and quadrature feedback voltage are the secondary correlation terms of the scale factor. By employing a weighted fusion of correlated terms through PLSR, the scale factor for temperature sensitivity is markedly enhanced by leveraging the predicted results to compensate for the output. The results indicate that the maximum error of the predicted scale factor is 0.124% within the temperature range of -40 °C to 60 °C, and the temperature sensitivity of the scale factor decreases from 6180 ppm/°C to 9.39 ppm/°C.

Negative piezoelectricity in quasi-two/one-dimensional ferroelectrics

Abstract In recent years, the investigation of low-dimensional ferroelectrics has attracted great attention for their promising applications in nano devices. Piezoelectricity is one of the most core properties of ferroelectric materials, which plays the essential role in micro-electromechanical systems. Very recently, the anomalous negative piezoelectricity has been predicted/discovered in many quasi-two-dimensional layered ferroelectric materials. In this Topical Review, we will briefly introduce on the negative piezoelectricity in quasi-two/one-dimensional ferroelectrics, including its fundamental concept, typical materials, theoretical predictions, as well as experimental phenomena. The underlying physical mechanisms for negative piezoelectricity are divergent and varying from case by case, which can be categorized into four types. First, the soft van der Waals layer is responsible for the volume shrinking upon pressure while the electric dipoles is from non van der Waals layer. Second, the noncollinearity of local dipoles creates a ferrielectricity, which leads to orthogonal ferroelectric and antiferroelectric axes. Third, the electric dipoles come from interlayer/interchain couplings, which can be enhanced during the volume shrinking. Fourth, the special buckling structure contributes to local dipoles, which can be enhanced upon pressure. In real materials, more than one mechanism may work together. Finally, the future directions of negative piezoelectricity and their potential applications are outlooked.