Microelectromechanical Systems Actuators Research Articles

Substrate dependence of the self-heating in lead zirconate titanate (PZT) MEMS actuators

Lead zirconate titanate (PZT) thin films offer advantages in microelectromechanical systems (MEMSs) including large motion, lower drive voltage, and high energy densities. Depending on the application, different substrates are sometimes required. Self-heating occurs in the PZT MEMS due to the energy loss from domain wall motion, which can degrade the device performance and reliability. In this work, the self-heating of PZT thin films on Si and glass and a film released from a substrate were investigated to understand the effect of substrates on the device temperature rise. Nano-particle assisted Raman thermometry was employed to quantify the operational temperature rise of these PZT actuators. The results were validated using a finite element thermal model, where the volumetric heat generation was experimentally determined from the hysteresis loss. While the volumetric heat generation of the PZT films on different substrates was similar, the PZT films on the Si substrate showed a minimal temperature rise due to the effective heat dissipation through the high thermal conductivity substrate. The temperature rise on the released structure is 6.8× higher than that on the glass substrates due to the absence of vertical heat dissipation. The experimental and modeling results show that the thin layer of residual Si remaining after etching plays a crucial role in mitigating the effect of device self-heating. The outcomes of this study suggest that high thermal conductivity passive elastic layers can be used as an effective thermal management solution for PZT-based MEMS actuators.

Broadband Microelectromechanical Systems‐Based Silicon Nitride Photonic Switch

Over the past three decades, silicon photonic devices have been core to the realization of large‐scale photonic‐integrated circuits. However, silicon nitride is another key complementary metal oxide semiconductor‐compatible material for high‐density photonic‐integrated circuits, having low manufacturing costs, low optical losses, and excellent mechanical properties, that can provide enhanced performance over silicon in an integrated photonic platform. This article presents the design, fabrication, and testing of a proof‐of‐concept switchable silicon nitride photonic coupler that leverages these properties combined with microelectromechanical systems actuation. The photonic platform uses a moveable suspended waveguide to enable efficient out‐of‐plane switching and is built using conventional lithographic techniques to demonstrate the high compatibility with existing microelectronic fabrication techniques. The photonic switch is measured to have an insertion loss of 2.6 dB and an ON/OFF extinction ratio of 34 dB at the output of the suspended waveguide, at a wavelength of 1470 nm. Detailed simulations demonstrate broadband operation over a 600 nm wavelength range from 1.25 to 1.85 μm which is experimentally validated over the range from 1.25 to 1.61 μm. To the best of knowledge, this is the broadest operation range ever demonstrated by a photonic switch in simulation.

Adaptive RBFNN‐based predictive control for the nanopositioning of an electrostatic MEMS actuator

AbstractElectrostatic micro electro mechanical system (MEMS) as an actuator is one of the most widely used actuators in micro dimension systems. Due to the high nonlinear characteristics in the micro actuator's model, nanopositioning has been a challenging problem for researchers. In addition, the system is subject to uncertainties associated with the system's unknown parameters and un‐modelled dynamics. Thus, to overcome these problems and achieve precise positioning a robust non‐linear control method is required. In this research, an optimal voltage control algorithm is initially designed utilizing the nonlinear predictive control approach. The Taylor expansion sequence is used to estimate the final position of the parallel plate actuator. To approximate unknown disturbances, a radial basis function neural network (RBFNN) has been designed. The estimations made were used in updating the control input in the previous step, and the obtained results showed an increase in the robustness of the designed controller. The stability of the closed‐loop system is also analyzed. Finally, a comparison is accomplished between the potential of the proposed controller and that of the feedback linearization and sliding mode controllers. The obtained results indicate better performance and robustness of the suggested controller.

Two-axis MEMS positioner for waveguide alignment in silicon nitride photonic integrated circuits.

Alignment is critical for efficient integration of photonic integrated circuits (PICs), and microelectromechanical systems (MEMS) actuators have shown potential to tackle this issue. In this work, we report MEMS positioning actuators designed with the ultimate goal of aligning silicon nitride (SiN) waveguides either to different outputs within a SiN chip or to active chips, such as lasers and semiconductor optical amplifiers. For the proof-of-concept, suspended SiN waveguides implemented on a silicon-on-insulator wafer were displaced horizontally in the direction of light propagation to close an initial gap of 6.92 µm and couple the light to fixed output waveguides located on a static section of the chip. With the gap closed, the suspended waveguides showed ∼ 345 nm out-of-plane misalignment with respect to the fixed waveguides. The suspended waveguides can be displaced laterally by more than ±2 µm. When the waveguides are aligned and the gap closed, an average loss of -1.6 ± 0.06 dB was achieved, whereas when the gap is closed with a ± 2 µm lateral displacement, a maximum average loss of ∼ -19.00 ± 0.62 dB was obtained. The performance of this positioner does not only pave the way for active chip alignment, but it could also be considered for optical switching applications.

Actively Tunable Spectral Filter for Compact Hyperspectral Camera Using Angle‐Sensitive Plasmonic Structures

AbstractHyperspectral imaging provides enhanced classification and identification of veiled features for diverse biomedical applications such as label‐free cancer detection or non‐invasive vascular disease diagnostics. However, hyperspectral cameras still have technical limitations in miniaturization due to the inherently complex and bulky configurations of conventional tunable filters. Herein, a compact hyperspectral camera using an active plasmonic tunable filter (APTF) with electrothermally driven spectral modulation for feature‐augmented imaging is reported. APTF consists of angle‐sensitive plasmonic structures (APS) over an electrothermal MEMS (Microelectromechanical systems) actuator, fabricated by combining nanoimprint lithography, and MEMS fabrication ona 6‐inch wafer. APS have a complementary configuration of Au nanohole and nanodisk arrays supported on asilicon nitride membrane. APTF shows a large angular motion at operational voltages of 5–9 VDC for continuous spectral modulation between 820 and 1000 nm (45 nm/V). The compact hyperspectral camera was fully packaged with a linear polarizer, APTF and amonochromatic camera, exhibiting asize of 16 mm (ϕ) × 9.5 mm (h). Feature‐augmented images of subcutaneous vein and a fresh fruit have been successfully demonstrated after the hyperspectral reconstruction and spectral feature extraction. This functional camera provides a new compact platform for point‐of‐care or in vivo hyperspectral imaging in biomedical applications.

Aluminum Nitride Out-of-Plane Piezoelectric MEMS Actuators

Integrating microelectromechanical systems (MEMS) actuators with low-loss suspended silicon nitride waveguides enables the precise alignment of these waveguides to other photonic integrated circuits (PICs). This requires both in-plane and out-of-plane actuators to ensure high-precision optical alignment. However, most current out-of-plane electrostatic actuators are bulky, while electrothermal actuators consume high power. Thus, piezoelectric actuators, thanks to their moderate actuation voltages and low power consumption, could be used as alternatives. Furthermore, piezoelectric actuators can provide displacements in two opposite directions. This study presents a novel aluminum nitride-based out-of-plane piezoelectric MEMS actuator equipped with a capacitive sensing mechanism to track its displacement. This actuator could be integrated within PICs to align different chips. Prototypes of the device were tested over the range of ±60 V, where they provided upward and downward displacements, and achieved a total average out-of-plane displacement of 1.30 ± 0.04 μm. Capacitance measurement showed a linear relation with the displacement, where at -60 V, the average change in capacitance was found to be -13.10 ± 0.89 fF, whereas at 60 V the change was 11.09 ± 0.73 fF. This study also investigates the effect of the residual stress caused by the top metal electrode, on the linearity of the displacement-voltage relation. The simulation predicts that the prototype could be modified to accommodate waveguide routing above it without affecting its performance, and it could also incorporate in-plane lateral actuators.

Extended and Generic Higher-Order Elements for MEMS Modeling

State-dependent resistors, capacitors, and inductors are a common part of many smart engineering solutions, e.g., in MEMS (Micro-Electro-Mechanical Systems) sensors and actuators, Micro/NanoMachines, or biomimetic systems. These memory elements are today modeled as generic and extended memristors (MR), memcapacitors (MC), and meminductors (ML), which are more general versions of classical MR, MC, and ML from the infinite set of the fundamental elements of electrical engineering, known as Higher-Order Elements (HOEs). It turns out that models of many complex phenomena in MEMS cannot be constructed only from classical and state-dependent elements such as R, L, and C, but that other HOEs with generalized behavior should also be used. Thus, in this paper, generic and extended versions of HOEs are introduced, overcoming the existing limitation to MR, MC, and ML elements. The relevant circuit theorems are formulated, which generalize the well-known theorems of classical memory elements, and their application to model complex processes of various physical natures in MEMS is shown.

A SOI Out-of-Plane Electrostatic MEMS Actuator Based on In-Plane Motion

This work describes a novel micromechanical structure capable of producing out-of-plane motion from in-plane forces generated by electrostatic microelectromechanical system (MEMS) actuators. The MEMS actuator is fabricated in a commercial silicon-on-insulator (SOI) MEMS process and is anchored at two distinct locations through a pair of beams with a relatively low stiffness in the vertical direction. A comb-drive, whose fixed and moveable fingers are implemented in the same layer with a uniform thickness, is employed to create an attractive electrostatic force. This in-plane electrostatic force rotates the actuator along an axis defined by the anchors, which results in the vertical motion of a suspended platform. Due to the simple structure of the actuator, it can be readily manufactured with standard bulk micromachining processes. Experimental results demonstrate that the actuator can provide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.02~\mu \text{m}$ </tex-math></inline-formula> of vertical displacement at a resonant frequency of 395 Hz when it is excited in air by a 10 V AC signal, while the displacement can be considerably increased in vacuum. It is further shown that the functionality of the actuator is not dependent on the type of excitation voltage; therefore, it can produce a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.09~\mu \text{m}$ </tex-math></inline-formula> static out-of-plane motion when excited by a 40 V DC voltage. A comprehensive comparison to the published works in the literature indicates that the proposed actuator is the only SOI electrostatic MEMS actuator with a relatively thick structural layer, i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\mu \text{m}$ </tex-math></inline-formula> , that can provide out-of-plane motion at low actuation voltage reported to date. [2022-0069]

Nonlinear actuation of micromechanical Casimir oscillators with topological insulator materials toward chaotic motion: Sensitivity on magnetization and dielectric properties.

We have investigated the dynamical actuation of micro-electromechanical systems under the influence of attractive and repulsive Casimir forces between topological insulator plates as a function of their dielectric function and coating magnetization. The analysis of the Casimir force in the limit of strong and weak magnetization shows that the attractive force, which is produced for plate magnetizations in the same direction, is greater than the repulsive force that is produced for opposite magnetizations. However, both forces remain comparable for intermediate magnetizations. Moreover, for weak magnetization, the attractive force becomes stronger for an increasing dielectric function, while the opposite occurs for the repulsive force. On the other hand, increasing magnetization decreases the influence of the dielectric function on both the repulsive and attractive forces. Furthermore, for conservative systems, bifurcation and phase portrait analysis revealed that increasing magnetization decreases the regime of stable operation for devices with attractive forces, while their operation remains always stable under the presence of repulsive forces. Finally, for non-conservative periodically driven systems, the Melnikov function and Poincaré portrait analysis show that for magnetizations in the same direction leading to strong attractive Casimir forces, chaotic motion toward stiction is highly likely to occur preventing the long-term prediction of actuating dynamics. A remedy for this situation is obtained by the application of any magnetization in opposite directions between the interacting surfaces since the repulsive force makes it possible to prevent stiction.

Integrated Amplitude and Phase Monitor for Micro-Actuators.

Micro-actuators driven on resonance maximize reach and speed; however, due to their sensitivity to environmental factors (e.g., temperature and air pressure), the amplitude and phase response must be monitored to achieve an accurate actuator position. We introduce an MEMS (microelectromechanical system) amplitude and phase monitor (MAPM) with a signal-to-noise ratio of 51 dB and 11.0 kHz bandwidth, capable of simultaneously driving and sensing the movement of 1D and 2D electrostatically driven micro-actuators without modifying the chip or its packaging. The operational principle is to electromechanically modulate the amplitude of a high-frequency signal with the changing capacitance of the micro-actuator. MAPM operation is characterized and verified by simultaneously measuring the amplitude and phase frequency response of commercial micromirrors. We demonstrate that the MAPM circuitry is insensitive to complex relationships between capacitance and position of the MEMS actuators, and it is capable of giving real-time read-out of the micromirror motion. Our measurements also reveal and quantify observations of phase drift and crosstalk in 2D resonant operation. Measurements of phase changes over time under normal operation also verify the need for phase monitoring. The open-loop, high-sensitivity position sensor enables detailed characterization of dynamic micro-actuator behavior, leading to new insights and new types of operation, including improved control of nonlinear motion.

Analysis of Ferroelectric Negative Capacitance-Hybrid MEMS Actuator Using Energy–Displacement Landscape

We propose an energy-based framework to analyze the statics and dynamics of a ferroelectric negative capacitance-hybrid Microelectromechanical System (MEMS) actuator. A mapping function that relates the charge on the ferroelectric to displacement of the movable electrode, is used to obtain the Hamiltonian of the hybrid actuator in terms of displacement. We then use graphical energy-displacement and phase portrait plots to analyze static pull-in, dynamic pull-in and pull-out phenomena of the hybrid actuator. Using these, we illustrate the low-voltage operation of the hybrid actuator to static and step inputs, as compared to the standalone MEMS actuator. The results obtained are in agreement with the analytical predictions and numerical simulations. The proposed framework enables straightforward inclusion of adhesion between the contacting surfaces, modeled using van der Waals force. We show that the pull-in voltage is not affected, while the pull-out voltage is reduced due to adhesion. The proposed framework provides a physics-based tool to design and analyze negative capacitance based low-voltage MEMS actuators.

Case Study of a MEMS Snap-Through Actuator: Modeling and Fabrication Considerations

MEMS actuators rely on the deformation of silicon structures. Using dimensions smaller than dozens of micrometers reveals that the micro-electro-mechanical systems (MEMS) actuators are affected by fabrication inaccuracies, leading to hardly predictable forces and/or actuation results. In this paper, MEMS bistable buckled beam actuators are presented. A series of structures based on pre-shaped buckled beams of lengths ranging from 2 to 4 mm, constant width of 5 μm and actuation stroke ranging from 20 to 100 μm was fabricated. Experimental data show a significant difference with predictions from a conventional analytical model. The model commonly used for buckled beams design assumes a rectangular beam section, but it is not the case of the fabricated beams. Furthermore, only symmetric buckling modes (mode 1, mode 3…) are supposed to exist during snap-through. In this paper, new analytical models have been developed on the basis of the models of the literature to consider the effective beam shape. The first improved analytical model enabled prediction of the MEMS buckled beams mechanical behavior in a 30% margin on the whole range of operation. A second model has been introduced to consider both the effective shape of the beam and centro-symmetric buckling modes. This refined model exhibits the partial suppression of buckling mode 2 by a central shuttle. Therefore, mode 2 and mode 3 coexist at the beginning and the end of snap-through, while mode 3 quickly vanishes due to increasing rotation of the central shuttle to leave exclusive presence of mode 2 near the mid-stroke. With this refined model, the effective force-displacement curve can be predicted in a margin reduced to a few percentages in the center zone of the response curve, allowing the accurate prediction of the position switch force. In addition, the proposed model allows accurate results to be reached with very small calculation time.

Adiabatic CMOS-Based Electrostatic MEMS Actuation for Reduced Dynamic Power and Switching Activity

The basic purpose of MEMS actuation is to miniaturize the actuators and sensors for applications in nanoelectronics. The transistor switching current and power supply noises due to voltage drops across the metal lines can impair circuit timing and performance, posing a continuing problem for high-performance chip designers. This work presents an empirical concept of a reconfigurable charge pump based on FPGA for electrostatic actuation of the Microelectromechanical System (MEMS). The goal of the design is to produce enough on-chip voltages for actuating the MEMS that are continuously adaptive and reconfigurable. In this proposed method, pumping capacitors lying in the range of 1-pF have been deployed to decrease the area of design concerned. The various voltages are programmable digitally and created by dynamically altering the number of phases as well as the clock drive levels. The dynamic model is designed by adjusting the number of stages to produce on-chip voltages including clock drive speeds, assuming a purely capacitive load. The proposed model’s power consumption can be lowered in the steady state by lowering its clock frequency and electrostatic MEMS actuators with capacitive load. An average of 0.62 W is dissipated by the circuit when the eight stages are triggered. Consequently, with adiabatic and without adiabatic architecture, 0.0186 mW of minimum power difference is obtained.

Strain-tuning of domain walls in multilayer graphene probed in the quantum Hall regime

Domain walls, topological defects that define the frontier between regions of different stacking in multilayer graphene, have proved to host exciting physics. The ability of tuning these topological defects in-situ in an electronic transport experiment brings a wealth of possibilities in terms of fundamental understanding of domain walls as well as for electronic applications. Here, we demonstrate through a MEMS (micro-electromechanical system) actuator and magnetoresistance measurements the effect of domain walls in multilayer graphene quantum Hall effect. Reversible and controlled uniaxial strain triggers these topological defects, manifested as new quantum Hall effect plateaus as well as a discrete and reversible modulation of the current across the device. Our findings are supported by theoretical calculations and constitute the first indication of the in-situ tuning of topological defects in multilayer graphene probed through electronic transport, opening the way to the use of reversible topological defects in electronic applications.

Piezoelectric MEMS—evolution from sensing technology to diversified applications in the 5G/Internet of Things (IoT) era

The rapid development of the fifth-generation mobile networks (5G) and Internet of Things (IoT) is inseparable from a large number of miniature, low-cost, and low-power sensors and actuators. Piezoelectric microelectromechanical system (MEMS) devices, fabricated by micromachining technologies, provide a versatile platform for various high-performance sensors, actuators, energy harvesters, filters and oscillators (main building blocks in radio frequency front-ends for wireless communication). In this paper, we provide a comprehensive review of the working mechanism, structural design, and diversified applications of piezoelectric MEMS devices. Firstly, various piezoelectric MEMS sensors are introduced, including contact and non-contact types, aiming for the applications in physical, chemical and biological sensing. This is followed by a presentation of the advances in piezoelectric MEMS actuators for different application scenarios. Meanwhile, piezoelectric MEMS energy harvesters, with the ability to power other MEMS devices, are orderly enumerated. Furthermore, as a representative of piezoelectric resonators, Lamb wave resonators are exhibited with manifold performance improvements. Finally, the development trends of wearable and implantable piezoelectric MEMS devices are discussed.

Ferroelectric and Ferroelastic Domain Related Formation and Influential Mechanisms of Vapor Deposited Piezoelectric Thin Films

Compared to the bulk piezoelectric materials counterpart, piezoelectric thin films (PTFs) possess advantages of smaller size, lower power consumption, better sensitivity, and have broad application in advanced micro-electro-mechanical system (MEMS) devices. However, the performance of MEMS transducers and actuators are largely limited by PTFs piezoelectric properties. In this review, we focus on understanding structure-property relationship of vapor deposited PTFs, with emphasis on the effect of strain energy and electrostatic energy in thin films, especially, energy relaxation induced misfit dislocation and ferroelectric (FS) and ferroelastic (FC) domain formation mechanisms. We then discuss the microstructure of these domains and their influential mechanisms on piezoelectric properties, as well as the domain engineering strategies (i.e., internal and external stimuli). This review will motivate further experimental, theoretical, and simulation studies on FS and FC domain engineering in PTFs.

Silicon photonic microelectromechanical phase shifters for scalable programmable photonics.

Programmable photonic integrated circuits are emerging as an attractive platform for applications such as quantum information processing and artificial neural networks. However, current programmable circuits are limited in scalability by the lack of low-power and low-loss phase shifters in commercial foundries. Here, we demonstrate a compact phase shifter with low-power photonic microelectromechanical system (MEMS) actuation on a silicon photonics foundry platform (IMEC's iSiPP50G). The device attains (2.9π±π) phase shift at 1550 nm, with an insertion loss of (0.33-0.10+0.15)dB, a Vπ of (10.7-1.4+2.2)V, and an Lπ of (17.2-4.3+8.8)µm. We also measured an actuation bandwidth f-3dB of 1.03 MHz in air. We believe that our demonstration of a low-loss and low-power photonic MEMS phase shifter implemented in silicon photonics foundry compatible technology lifts a main roadblock toward the scale-up of programmable photonic integrated circuits.

Analysis of thermo-mechanical coupling damage behavior in long-term performance of microelectromechanical systems actuators

Effective numerical analysis is significant for the optimal design and reliability evaluation of MEMS, but the complexity of multi-physical field couplings and irreversible damage accumulation in long-term performance make the analysis difficult. In the present paper, the continuum damage mechanics method is used to develop a creep damage model and conduct long-term performance analysis for MEMS thermal actuators with coupled thermo-mechanical damage behavior. The developed damage model can make a connection between the material deterioration due to microstructure changes and the macroscopic responses (the change of thermo-mechanical performance or structure failure). The numerical simulations of coupled thermo-mechanical behavior in long-term performance are implemented using the finite element method, which is validated through comparison with previous literature. The numerical results demonstrate that the proposed damage model and numerical method can provide effective assessment in the long-term performance of MEMS thermal actuators.

Analysis of Flexural Vibrations of a Piezoelectric Semiconductor Nanoplate Driven by a Time-Harmonic Force.

The performance of devices fabricated from piezoelectric semiconductors, such as sensors and actuators in microelectromechanical systems, is superior; furthermore, plate structures are the core components of these smart devices. It is thus important to analyze the electromechanical coupling properties of piezoelectric semiconductor nanoplates. We established a nanoplate model for the piezoelectric semiconductor plate structure by extending the first-order shear deformation theory. The flexural vibrations of nanoplates subjected to a transversely time-harmonic force were investigated. The vibrational modes and natural frequencies were obtained by using the matrix eigenvalue solver in COMSOL Multiphysics 5.3a, and the convergence analysis was carried out to guarantee accurate results. In numerical cases, the tuning effect of the initial electron concentration on mechanics and electric properties is deeply discussed. The numerical results show that the initial electron concentration greatly affects the natural frequency and electromechanical fields of piezoelectric semiconductors, and a high initial electron concentration can reduce the electromechanical fields and the stiffness of piezoelectric semiconductors due to the electron screening effect. We analyzed the flexural vibration of typical piezoelectric semiconductor plate structures, which provide theoretical guidance for the development of new piezotronic devices.

High speed external cavity diode laser concept based on a resonantly driven MEMS scanner for the mid-infrared region.

The rapid detection of trace gases is of great relevance for various spectroscopy applications. In this regard, the technology of external cavity diode lasers (ECDLs) has firmly established itself due to its excellent properties. Outside of the laboratory environment, however, these still have some restrictions, especially with regard to high acquisition rates for sensitive spectroscopy applications and mode-hop-free tuning. In this article, we present our innovative GaSb-based ECDL concept, in which a resonantly driven microelectromechanical system actuator is used. With this, a defined frequency range can be tuned extremely fast and without mode hops. Results of the characterization and its use for the rapid detection of trace gases are presented.