Microelectromechanical Actuators Research Articles

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.

Vacuum-sealed silicon photonic MEMS tunable ring resonator with an independent control over coupling and phase.

Ring resonators are a vital element for filters, optical delay lines, or sensors in silicon photonics. However, reconfigurable ring resonators with low-power consumption are not available in foundries today. We demonstrate an add-drop ring resonator with the independent tuning of round-trip phase and coupling using low-power microelectromechanical (MEMS) actuation. At a wavelength of 1540 nm and for a maximum voltage of 40 V, the phase shifters provide a resonance wavelength tuning of 0.15 nm, while the tunable couplers can tune the optical resonance extinction ratio at the through port from 0 to 30 dB. The optical resonance displays a passive quality factor of 29 000, which can be increased to almost 50 000 with actuation. The MEMS rings are individually vacuum-sealed on wafer scale, enabling reliable and long-term protection from the environment. We cycled the mechanical actuators for more than 4 × 109 cycles at 100 kHz, and did not observe degradation in their response curves. On mechanical resonance, we demonstrate a modulation increase of up to 15 dB, with a voltage bias of 4 V and a peak drive amplitude as low as 20 mV.

Reconfigurable Split Ring Resonators by MEMS-Driven Geometrical Tuning.

A novel approach for dynamic microwave modulation is proposed in the form of reconfigurable resonant circuits. This result is obtained through the monolithic integration of double split ring resonators (DSRRs) with microelectromechanical actuators (MEMS) for geometrical tuning. Two configurations were analyzed to achieve a controlled deformation of the DSRRs' metamaterial geometry by mutual rotation or extrusion along the azimuthal direction of the two constituent rings. Then, the transfer function was numerically simulated for a reconfigurable MEMS-DSRR hybrid architecture where the DSRR is embedded onto a realistic piezo actuator chip. In this case, a 370 MHz resonance frequency shift was obtained under of a 170 µm extrusion driven by a DC voltage. These characteristics in combination with a high Q factor and dimensions compatible with standard CMOS manufacturing techniques provide a step forward for the production of devices with applications in multiband telecommunications and wireless power transfer and in the IoT field.

Applications of flexible and stretchable three-dimensional structures for soft electronics

The development of devices that can be mechanically deformed in geometrical layouts, such as flexible/stretchable devices, is important for various applications. Conventional flexible/stretchable devices have been demonstrated using two-dimensional (2D) geometry, resulting in dimensional constraints on device operations and functionality limitations. Accordingly, expanding the dimensions in which such devices can operate and acquiring unique functionality that is difficult to implement in 2D planar structures remain challenging. As a solution, the development of a flexible/stretchable device embedding a three-dimensional (3D) structure fabricated through the precise control of a 2D structure or direct construction has been attracting significant attention. Because of a significant amount of effort, several 3D material systems with distinctive engineering properties, including electrical, optical, thermal, and mechanical properties, which are difficult to occur in nature or to obtain in usual 2D material systems, have been demonstrated. Furthermore, 3D advanced material systems with flexibility and stretchability can provide additional options for developing devices with various form factors. In this review, novel fabrication methods and unprecedented physical properties of flexible/stretchable 3D material systems are reviewed through multiple application cases. In addition, we summarized the latest advances and trends in innovative applications implemented through the introduction of advanced 3D systems in various fields, including microelectromechanical systems, optoelectronics, energy devices, biomedical devices, sensors, actuators, metamaterials, and microfluidic systems.

Internal resonance in a MEMS levitation force resonator

In this work, we explore internal resonances in a levitation force microelectromechanical system-based actuator assuming flexible cantilever and clamped–clamped microbeam configurations. The levitation force is generated through a special arrangement of two-side stationary charged substrates and a central grounded stationary strip. The design assumes as well an upper flexible microbeam strip. The DC part of the excitation voltage pushes up the moving microbeam away from its lower stationary electrode. A superimposed harmonic AC voltage lets the flexible strip vibrate around its equilibrium position. Energy exchange among the computed lower vibration frequencies and their respective frequency and force response curves are explored for possibilities of principal parametric and internal resonances interactions. The generated responses are computed using the bifurcation toolbox MatCont. The effect of Von Karman nonlinearity to power the energy exchange within vibration modes is explored and dominant factors in the MEMS design for resonances are found from a two-parameter bifurcation analysis. Our results allow optimizing the micro-actuator device performance for future applications.

An On-Chip Liquid Metal Plug Generator.

Gallium-based liquid metal nonspherical droplets (plugs) have seen increasing demand recently mainly because their high aspect ratios make them beneficial for a wide range of applications, including microelectromechanical systems (MEMS), microfluidics, sensor technology, radio-frequency devices, actuators, and switches. However, reproducibility of the generation of such plugs, as well as precise control over their size, is yet challenging. In this work, a simple on-chip liquid metal plug generator using a commercially available 3D microprinter is presented and the plug generator in poly(dimethylsiloxane) is replicated via soft lithography. Liquid metal plugs are generated via a combination of electrochemical oxidation, design of well-defined constrictions based on Laplace pressure, and the application of modulated voltage control signals. It is shown that plugs of various aspect ratios can be generated reproducibly for channel widths of 0.5, 0.8, and 1.5mm with constriction widths of 0.1mm at 6V. Laplace-pressure-controlled plugs in constricted channels are compared to modulated-voltage-generated plugs in straight channels showing that this technique provides significantly enhanced reproducibility and control over the size and spacing between the plugs. This work paves the way to sub-millimeter liquid metal plugs generated directly on-chip for on-demand MEMS and microfluidic applications.

Fabricating Silicon Resonators for Analysing Biological Samples.

The adaptability of microscale devices allows microtechnologies to be used for a wide range of applications. Biology and medicine are among those fields that, in recent decades, have applied microtechnologies to achieve new and improved functionality. However, despite their ability to achieve assay sensitivities that rival or exceed conventional standards, silicon-based microelectromechanical systems remain underutilised for biological and biomedical applications. Although microelectromechanical resonators and actuators do not always exhibit optimal performance in liquid due to electrical double layer formation and high damping, these issues have been solved with some innovative fabrication processes or alternative experimental approaches. This paper focuses on several examples of silicon-based resonating devices with a brief look at their fundamental sensing elements and key fabrication steps, as well as current and potential biological/biomedical applications.

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.

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.

A torsional thrust stand for measuring the thrust response time of micro-Newton thrusters

Drag-free technology functions as the keystone for space-based gravitational wave detection satellites moving along a geodesic path, like the Laser Interferometer Space Antenna (LISA) Pathfinder, to achieve ultra-high microgravity level. Several prerequisites for micro-thrusters operated under the drag-free technique include constantly adjustable thrust, high resolution, low noise and fast response time. Accordingly, a torsional thrust measurement system was methodically devised to measure the thrust response time of such micro-thrusters on the ground. The characteristics of the dynamic thrust change with time are inverted by the angular displacement of the torsional pendulum, established by the dynamic equation of the same, thus, measuring the rise/fall time of the thrust applied to the torsional pendulum. Calibration of the torsional pendulum thrust measurement system is carried out by the standard electrostatic force generated by the electrostatic comb-drive or microelectromechanical actuator, facilitating the suitable identification of the pendulum parameters. Afterwards, the electrostatic and electromagnetic forces generated by the actuator are applied to validate the measurable thrust response time of the torsional thrust stand. The experimental results show that the above-mentioned thrust stand can effectively measure the thrust response time up to 10 ms for a thrust step in 10 s of micronewtons, which qualifies as the thrust response time required by micro-thrusters for space-based gravitational wave detection.

Positional Regulation of Electrostatic Micro-electromechanical Actuator via Adaptive Two-stage Sliding Mode Control

Positional Regulation of Electrostatic Micro-electromechanical Actuator via Adaptive Two-stage Sliding Mode Control

Versatile Movements of Liquid Metal Droplet under Electrostatic Actuation in Alkaline Solutions.

The gallium-based eutectic liquid metal alloys exhibit unique properties of deformability, excellent electrical conductivity and low vapour pressure. The liquid metal-based circuits’ element or actuator have drawn considerable attention in stretchable electronics and microelectromechanical (MEMS) actuators. Yet, the motion of the liquid metal within the electrolyte needs to be precisely regulated to satisfy application requirements. Herein, we investigated the locomotion of liquid metal within the alkaline aqueous solution under electrostatic actuation. The relationship between the travelling speed of the liquid metal slug and the relative influential parameters, such as the voltage amplitude and frequencies of the applied electric field, electrolyte concentration, electrodes distance and the liquid metal volume, were experimentally characterized. A travelling speed up to 20.33 mm/s was obtained at the applied voltage of 4 Vpp at 150 Hz at 6 V DC offset. Finally, the frequency-dependent liquid metal marble movements were demonstrated, namely oscillation and forward locomotion while oscillating. The oscillation frequency was determined by the frequency of the applied alternate current (AC) signal. The remarkable transportation and oscillating characteristic of the liquid metal marble under the electrostatic actuation may present potentials towards the development of flexible electronics and reconfigurable structures.

Piezoelectric Actuators and Motors: Materials, Designs, and Applications

AbstractPiezoelectric actuators are unique driving force‐generation devices, which can transfer input electric energy into force, displacement, or movement outputs efficiently and precisely via piezoelectric effect‐based electromechanical coupling instead of electromagnetic induction. In comparison with traditional electromagnetic actuators, the most important features of the piezoelectric actuators are their compact size, flexible design, and ability to provide nanometer or sub‐micrometer positioning. Here, recent progress in nonresonance piezoelectric actuators including multilayer ceramic actuators, step motors, inertial motors, and resonance ultrasonic motors, such as linear motors, rotary motors, multidegree of freedom motors, and microelectromechanical system actuators, is comprehensively presented. The working principles and properties of these actuators are explained, and the piezoelectric materials and configurations, fabrication, and applications are provided. Furthermore, from the aspects of materials, designs and applications, challenges and outlooks for future developments of piezoelectric actuators and motors are also discussed.

Characteristics of drop-on-demand droplet jetting with effect of altered geometry of printhead nozzle

As a precision micro-electromechanical actuator, the geometry of drop-on-demand (DoD) printhead nozzle could be altered resulting from the accumulated manufacturing tolerances (AMT) and partial nozzle clogging (PNC) which largely influences the droplet jetting dynamics. To explore the effect of altered nozzle geometry on the DoD droplet formation characteristics, a three-dimensional (3D) multi-relaxation-time (MRT) lattice Boltzmann (LB) model coupled with nonideal nozzle plate wettability is presented to handle the complex droplet jetting process. For typical Z=11.57, with the hydrophobic nozzle plate, the velocities of final droplet are increased with the nozzle volume decreasing θN=49° and PNC. The non-ideal hydrophilic nozzle plate could eliminate the effect of altered nozzle geometry which exhibits the identical trajectories of droplet jetting. As Z number increasing to Z=19.8, the overall velocities of liquid filaments and resulting droplets are increased considerably. However, the effect of AMT decreases the velocity of filament tail and the recombination of satellite and main droplets could not occur for θN=49° which is undesirable for DoD inkjet printing. For case of PNC, the leftward deviation of recombined droplet is increased for the non-ideal hydrophilic nozzle plate and large Z number which greatly deteriorates the droplet jetting directionality.

Modeling and Thermal Metrology of Thermally Isolated MEMS Electrothermal Actuators for Strain Engineering of 2D Materials in Air

We present electrothermal microelectromechanical (MEMS) actuators as a practical platform for straining 2-D materials. The advantages of the electrothermal actuator are its high output force and displacement for low input voltage, but its drawback is that it is actuated by generating high amounts of heat. It is crucial to mitigate the high temperatures generated during actuation for reliable 2-D material strain device implementation. Here, we implement a chevron actuator design that incorporates a thermal isolation stage in order to avoid heating the 2-D material from the high temperatures generated during the actuation. By comparing the experiment and simulation, we ensure our design does not compromise output displacement while keeping the 2-D material strain device stage cool. We also provide a simple analytical model useful for quickly evaluating different thermal isolation stage designs.

Poly(3,4‐ethylenedioxythiophene):Poly(styrene sulfonate)/Polyethylene Oxide Electrodes with Improved Electrical and Electrochemical Properties for Soft Microactuators and Microsensors

AbstractThe development of microsystems is a rapidly evolving field which enables a wide range of applications for electroactive materials. Microelectromechanical actuators based on electronically conducting polymers are elaborated with an up‐scalable process. Commercial poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is chosen as an easily processable electrode to ensure the reproducibility for further technological production and practical applications. First, the improvement of electrical, electrochemical, and mechanical properties of the PEDOT:PSS electrodes is described by incorporating reactive additives, that is, glycol‐based monomers (mPEG) as polyethylene oxide (PEO) network precursors. Moreover, the custom fit layer‐by‐layer (LbL) process to integrate these PEDOT:PSS/PEO composite electrodes into trilayer microactuators is presented. The incorporation of PEO within PEDOT:PSS improves significantly the electromechanical performances of the resulting microactuators with significant strain (0.82%) and high output forces (472 µN) compared to similar PEDOT based or pristine PEDOT:PSS microactuators. This work provides also the first demonstration that mechanical strain sensing behavior, extensively studied at macroscale, still occurs at microscale for these trilayer systems. Additionally, to this proof of concept, it highlights that output signal is significantly enhanced by downsizing the devices compared to similar macroscale samples. These results open promising perspectives in the development of numerous applications for soft and scalable microactuators and microsensors.

Low-power optical beam steering by microelectromechanical waveguide gratings.

Optical beam steering is key for optical communications, laser mapping (lidar), and medical imaging. For these applications, integrated photonics is an enabling technology that can provide miniaturized, lighter, lower-cost, and more power-efficient systems. However, common integrated photonic devices are too power demanding. Here, we experimentally demonstrate, for the first time, to the best of our knowledge, beam steering by microelectromechanical (MEMS) actuation of a suspended silicon photonic waveguide grating. Our device shows up to 5.6° beam steering with 20V actuation and power consumption below the μW level, i.e., more than five orders of magnitude lower power consumption than previous thermo-optic tuning methods. The novel combination of MEMS with integrated photonics presented in this work lays ground for the next generation of power-efficient optical beam steering systems.

Dimpled electrostatic MEMS actuators

We present electrostatic Micro-Electromechanical System actuators equipped with dimples and contact pads. The introduction of dimples and contact pads is shown to prevent stiction between the actuator and bottom electrodes and minimize dielectric charging and to eliminate multi-valuedness in the response. It also increases the stable travel range by eliminating the pull-in instability and introducing new “tapping mode” oscillations, where the dimples come into regular contact with the contact pads. An experimentally validated lumped-mass model was developed and used to generate the bifurcation diagram of the actuator in the vicinity of tapping mode oscillations. The diagram showed the presence of a chaotic attractor bracketed by a type-I intermittency and a cascade of period-doubling bifurcations. However, these chaotic motions were only present for a limited range of the excitation amplitude and frequency. Provided these ranges are excluded, dimples and contact pads can be deployed to obtain efficient and well regulated electrostatic actuators. We found that these results and conclusions are valid for classes of low-frequency as well as high-frequency actuators.

Preparation of high-quality stress-free (001) aluminum nitride thin film using a dual Kaufman ion-beam source setup

We proposed and demonstrated a preparation method of (001) preferentially oriented stress-free AlN piezoelectric thin films. The AlN thin films were deposited by a reactive sputtering technique at substrate temperatures up to 330 °C using a dual Kaufman ion-beam source setup. We deposited the AlN on Si (100), Si (111), amorphous SiO2, and a (001) preferentially oriented Ti thin film and compared their crystallographic, optical, and piezoelectric properties. The AlN thin films deposited on the (001) preferentially oriented Ti thin films have the highest crystallographic quality. The stress-free AlN reached a high value of the piezoelectric coefficient d33 = (7.33 ± 0.08) pC·N−1. The properties of the AlN thin film prepared at such low temperatures are suitable for numerous microelectromechanical systems, piezoelectric sensors, and actuators monolithically integrated with complementary metal-oxide-semiconductor signal-processing circuits.

A Novel Transmitting Module Self-Monitoring Protection System Based On MEMS Sensors and Actuators

Design, fabrication, and measurements of a novel transmitting module self-monitoring protection system are presented in this letter. Such a system is based on microelectromechanical systems (MEMS) sensors and actuators for monitoring and protecting the microwave amplifier circuit. The transmitting module self-monitoring protection system consists of the RF MEMS switches, the directional coupler, and the MEMS power sensors. When the microwave amplifier circuit is at an abnormal state (“open,” “short,” or “overload”), the transmitting module self-monitoring protection system can isolate the microwave amplifier circuit out of order and reconfigure the transmitting module into impedance matching within 36 ms. When the microwave amplifier circuit is at the overload state, the error between the set switching power and the actual switching power is less than 9%. The measured results agree well with the theory.