Microelectromechanical Resonators Research Articles

AlScN-on-SiC microelectromechanical Lamb wave resonators operating at high temperature up to 800 °C

We report on the experimental demonstration of aluminum scandium nitride (AlScN)-on-cubic silicon carbide (3C-SiC) Lamb wave resonators (LWRs) realized via microelectromechanical systems (MEMS) technology, operating at high temperature (T) up to T = 800 °C, while retaining robust electromechanical resonances at ∼27 MHz and good quality factor of Q ≈ 900 even at 800 °C. Measured resonances exhibit clear consistency and stability during heating and cooling processes, validating the AlScN-on-SiC LWRs can operate at high T up to 800 °C without noticeable degradation in moderate vacuum (∼20 mTorr). Even after undergoing four complete thermal cycles (heating from 23 to 800 °C and then cooling down to 23 °C), the devices exhibit robust resonance behavior, suggesting excellent stability and suitability for high-temperature applications. Q starts to decline as the temperature exceeds 400 °C, which can be attributed to energy dissipation mechanisms stemming from thermoelastic damping and intrinsic material loss originating from phonon–phonon interactions.

AlScN-on-SiC microelectromechanical Lamb wave resonators operating at high temperature up to 800 °C

We report on the experimental demonstration of aluminum scandium nitride (AlScN)-on-cubic silicon carbide (3C-SiC) Lamb wave resonators (LWRs) realized via microelectromechanical systems (MEMS) technology, operating at high temperature (T) up to T = 800 °C, while retaining robust electromechanical resonances at ∼27 MHz and good quality factor of Q ≈ 900 even at 800 °C. Measured resonances exhibit clear consistency and stability during heating and cooling processes, validating the AlScN-on-SiC LWRs can operate at high T up to 800 °C without noticeable degradation in moderate vacuum (∼20 mTorr). Even after undergoing four complete thermal cycles (heating from 23 to 800 °C and then cooling down to 23 °C), the devices exhibit robust resonance behavior, suggesting excellent stability and suitability for high-temperature applications. Q starts to decline as the temperature exceeds 400 °C, which can be attributed to energy dissipation mechanisms stemming from thermoelastic damping and intrinsic material loss originating from phonon–phonon interactions.

Highly Reliable Diamond MEMS Dual Sensor for Magnetic Fields and Temperatures with Self‐Recognition Algorithms

AbstractNearly all sensors inevitably suffer from environmental influence such as temperature fluctuation. To precisely process the external signals, independent temperature compensation devices or electronic circuits are usually required, making the overall system and algorithms sophisticated. Especially, when the environment temperature is as high as over 200 °C, both the sensors and temperature‐compensation devices encounter the reliability problem. In this work, an intelligent multifunctional sensor utilizing single‐crystal diamond (SCD) microelectromechanical (MEMS) resonators is demonstrated that can sense both magnetic fields and temperatures up to 300 °C, independently. The strategy is to integrate a magnetostrictive thin film and a non‐magnetic thin film on different diamond MEMS resonators on the same diamond chip for simultaneous magnetic field sensing and temperature monitoring, respectively. The multi‐resonators based on diamond MEMS offer a promising platform for multi‐parameter sensing immune to environment interference.

Metal Microelectromechanical Resonator Exhibiting Fast Human Activity Detection.

This work presents a MEMS resonator used as an ultra-high resolution water vapor sensor (humidity sensing) to detect human activity through finger movement as a demonstrator example. This microelectromechanical resonator is designed as a clamped-clamped beam fabricated using the top metal layer of a commercial CMOS technology (0.35 μm CMOS-AMS) and monolithically integrated with conditioning and readout circuitry. Sensing is performed through the resonance frequency change due to the addition of water onto the clamped-clamped beam coming from the moisture created by the evaporation of water in the human body. The sensitivity and high-speed response to the addition of water onto the metal bridge, as well as the quick dewetting of the surface, make it suitable for low-power human activity sensing.

Anchor Loss Reduction in Micro-Electro Mechanical Systems Flexural Beam Resonators Using Trench Hole Array Reflectors.

The quality factor of microelectromechanical resonators is a crucial performance metric and has thus been the subject of numerous studies aimed at maximizing its value by minimizing the anchor loss. This work presents a study on the effect of elastic wave reflectors on the quality factor of MEMS clamped-clamped flexural beam resonators. The elastic wave reflectors are a series of holes created by trenches in the silicon substrate of the resonators. In this regard, four different shapes of arrayed holes are considered, i.e., two sizes of squares and two half circles with different directions are positioned in proximity to the anchors. The impact of these shapes on the quality factor is examined through both numerical simulations and experimental analysis. A 2D in-plane wave propagation model with a low-reflecting fixed boundary condition was used in the numerical simulation to predict the behavior, and the MEMS resonator prototypes were fabricated using a commercially available micro-fabrication process to validate the findings. Notably, the research identifies that half-circle-shaped holes with their curved sides facing the anchors yield the most promising results. With these reflectors, the quality factor of the resonator is increased by a factor of 1.70× in air or 1.72× in vacuum.

Impact of Silicon Ion Irradiation on Aluminum Nitride‐Transduced Microelectromechanical Resonators

AbstractMicroelectromechanical systems (MEMS) resonators use is widespread, from electronic filters and oscillators to physical sensors such as accelerometers and gyroscopes. These devices' ubiquity, small size, and low power consumption make them ideal for use in systems such as CubeSats, micro aerial vehicles, autonomous underwater vehicles, and micro‐robots operating in radiation environments. Radiation's interaction with materials manifests as atomic displacement and ionization, resulting in mechanical and electronic property changes, photocurrents, and charge buildup. This study examines silicon (Si) ion irradiation's interaction with piezoelectrically transduced MEMS resonators. Furthermore, the effect of adding a dielectric silicon oxide (SiO2) thin film is unveiled. Aluminum nitride on silicon (AlN‐on‐Si) and AlN‐SiO2‐Si bulk acoustic wave (BAW) resonators are designed and fabricated. The devices are irradiated using 2 MeV Si+ ions at various fluxes up to a total fluence of 5 × 1014 cm−2. A time anneal is conducted to characterize device recovery. Scattering (S‐) parameters are measured in situ. Specific damage coefficients are derived to describe the radiation effect on resonant frequency (fr), quality factor (Q), motional resistance (Rm), and electromechanical coupling factor (). Furthermore, the damage coefficients for the bulk material properties of elastic modulus (E) and the piezoelectric coefficient (d31) are found.

Effects of Gamma Ray Radiation on the Performance of Microelectromechanical Resonators

Effects of Gamma Ray Radiation on the Performance of Microelectromechanical Resonators

Effects of Gamma Ray Radiation on the Performance of Microelectromechanical Resonators

While much radiation test data are available for metal‐oxide‐semiconductor (MOS) devices, research into the effects of radiation on microelectromechanical systems (MEMS) is in its relative infancy. Piezoelectrically transduced MEMS resonators have broad applications in signal processing, environmental monitoring, and navigation. Aluminum nitride (AlN), in particular, is an attractive piezoelectric because of its favorable fabrication characteristics and ease of integration into the complementary MOS (CMOS) manufacturing process. The utility of these devices in space and nuclear systems necessitates research into their performance in radiation environments. Resiliency and an established relationship between radiation dose and device behavior provide a critical tool for engineers in their design process. Multiple AlN‐based MEMS resonator designs are created and exposed the devices to 1 Mrad(Si) gamma irradiation from a Cobalt‐60 source while measuring scattering (S‐) parameters in situ. The experimental data are matched to a theoretical model to describe the change in frequency as a function of radiation‐induced displacement damage. It is demonstrated that the AlN‐based resonators are resilient against radiation‐induced charge‐trapping effects. Furthermore, a new method is presented of permanent frequency trimming MEMS resonators up to 30% of their bandwidth without modifying quality factor or motional resistance.

Using a Photoacoustic Cell for Spectroscopy of Toxic Air Pollutants including CO2, SO2 and NO Gases

Due to the rise in global temperature and climate change, the detection of CO2, SO2 and NO pollutants is important in smart cities. In this paper, an H-shaped photoacoustic cell is utilized for the detection of low-concentration gases. The geometry of the cell is miniaturized and designed with specific parameters in order to increase its efficiency and performance. The designed cell eliminates problems such as bulkiness and cost, which prevent the use of sensors in detecting greenhouse gases. The simplicity of the design expands the application rate of the cell in practice. In order to consider the viscosity and thermal effects, the cell is formulized by fully linearized Navier–Stokes equations, and various parameters, such as acoustic pressure, frequency response, sound speed (sound velocity) and quality factor, are investigated for the mentioned gases. The performance of the system is frequency-based, and the target gases can be detected by using a microelectromechanical resonator as a pressure sensor. Quality factor analysis expresses that CO2, SO2 and NO gases have quality factors of 27.84, 33.62 and 33.32, respectively. The performance of the cell in the resonance state can be expressed by the linear correlation between the results. The background noise generated in the photoacoustic research has been removed by miniaturization due to the obtained resonance, and the proposed cell provides a proper signal-to-noise ratio. The results of the proposed system represent the increase in the quality factor, which reduces the losses and thus increases the sensitivity of the system in the study of greenhouse gases.

Thermoelastic damping in micro-scale T-, U- and Z-shaped frame structures using wave propagation approach

Studying the thermo-mechanical coupling behavior and establishing the thermoelastic damping (TED) model are essential for improving the quality factor of the microelectromechanical resonator. In this work, an analytical TED model for planar frame resonators is first developed using the wave propagation approach. The method is illustrated for typical T-, U- and Z-shaped frame structures and can be extended to more complex frame structures. The frame is viewed as a set of beam segments interconnected by rigid joints, each following the Euler-Bernoulli beam theory. Based on the wave propagation approach, the wave transmission and reflection properties at discontinuities are determined taking into account the flexural and longitudinal motions. The displacement fields of the frame structure are established for both free and forced vibrations. The coupled temperature field of the frame is obtained by solving for the temperature variation arising from the flexural and longitudinal vibrations separately. Finally, the expression of TED is achieved by its energy definition. The validity of the present TED model is confirmed by comparison with finite element (FE) simulations. Numerical results indicate that the TED behavior of frame structures is too complicated to be predicted by previous TED models of simple structures. The often-overlooked longitudinal motion will cause a dramatic TED reduction around specific frequencies. The overall TED is determined by all segments together, and the influence of a segment is reflected by its energy share. Moreover, the effects of different boundary conditions and geometric parameters on TED are evaluated. Practical conclusions to guide the design of high Q-factor resonators are drawn based on the TED behavior of frame structures as summarized from the numerical study.

Generation of Electromechanical Frequency Combs in Fluid Media with a Parametrically Driven Capacitive Microresonator

The generation of electromechanical frequency combs in both air and liquid environments using a capacitive microresonator array is presented in this paper. In contrast to frequency-comb generation in purely mechanical resonators, we show that the damping-dependent threshold for comb generation can be reduced by parametrically coupling a resonant electrical circuit to the mechanical resonator. A one-dimensional lumped parameter model of the proposed system is presented and semianalytical solutions are developed to investigate the parameters influencing frequency-comb formation under various operating conditions. The results obtained with numerical simulations are experimentally validated using a commercially available microelectromechanical resonator, and frequency combs with a repetition rate sensitive to the force on the mechanical resonator are generated with a single electrical drive in air and in a liquid-filled microfluidic channel. In contrast to prior work on electromechanical frequency combs, this work represents a simple yet robust approach to generating stable combs, thereby enabling its practical use in applications, such as gas sensing and microfluidics.

Nanoscale imaging of super-high-frequency microelectromechanical resonators with femtometer sensitivity

Implementing microelectromechanical system (MEMS) resonators calls for detailed microscopic understanding of the devices, such as energy dissipation channels, spurious modes, and imperfections from microfabrication. Here, we report the nanoscale imaging of a freestanding super-high-frequency (3 – 30 GHz) lateral overtone bulk acoustic resonator with unprecedented spatial resolution and displacement sensitivity. Using transmission-mode microwave impedance microscopy, we have visualized mode profiles of individual overtones and analyzed higher-order transverse spurious modes and anchor loss. The integrated TMIM signals are in good agreement with the stored mechanical energy in the resonator. Quantitative analysis with finite-element modeling shows that the noise floor is equivalent to an in-plane displacement of 10 fm/√Hz at room temperatures, which can be further improved under cryogenic environments. Our work contributes to the design and characterization of MEMS resonators with better performance for telecommunication, sensing, and quantum information science applications.

Influence of a Tailored Oxide Interface on the Quality Factor of Microelectromechanical Resonators (Adv. Mater. Interfaces 9/2023)

Microelectromechanical Resonators The cover art illustrates an aluminum nitride transduced microelectromechanical resonators, as described by David D. Lynes and Hengky Chandrahalim in article number 2202446. By including a tailored oxide thin film in the resonator's body, the quality factor is increased by up to 400% for devices operating at very high frequency and super high frequency bands. The quality factor enhancement persists at operating temperatures as low as −200 °C up to +200 °C.

Influence of a Tailored Oxide Interface on the Quality Factor of Microelectromechanical Resonators

AbstractPiezoelectric microelectromechanical systems (MEMS) are used as sensors, actuators, energy harvesters, accelerometers, and communication modules. Aluminum nitride (AlN) is an especially attractive piezoelectric material because its fabrication process allows it to be integrated into semiconductor circuitry to deliver a fully integrated solution. Microelectromechanical resonators with AlN sandwiched between n‐type silicon (Si) and top metal electrode with and without a silicon oxide layer are designed and fabricated. The effect of the oxide film is up to a fourfold increase in quality factor (Q) that is consistent from very high frequency (VHF) to super high frequency (SHF). This effect is demonstrated using thin plate bulk acoustic wave modes from 70–80 MHz using the second contour mode and first width extensional mode and from 9.5–10.5 GHz using high overtone thickness modes. To explore potential applications of AlN‐transduced Q‐enhanced MEMS devices in harsh environments, measurements from −200 °C to +200 °C are performed. The Q enhancement is persistent across a wide temperature range for both VHF and SHF resonators with the added oxide layer. Furthermore, AlN‐on‐Si resonators that have a comparable temperature coefficient of frequency to silicon carbide‐based resonators in commercial applications are demonstrated.

Investigation and reduction of finite width effect of coupling beam in bandwidth estimation of coupled MEMS resonator

AbstractBand pass filters are realized by coupled microelectromechanical resonators and their bandwidth is determined by the ratio of coupling beam stiffness to resonator beam stiffness at the coupling location. The coupling beam is connected to the resonator beam in such a way that the resonator beam length and coupling beam width are in the same axis. Practically, it is not possible for the coupling beam to make contact with the resonator beam at a single point. But presently, coupled resonators are designed for specific bandwidth by considering resonator beam stiffness at any point within the contact area between the coupling beam and resonator beam. Due to the finite width of the coupling beam, resonator stiffness at the coupling location is multivalued. It causes additional velocity coupling. So, the bandwidth calculated using single‐point stiffness on the resonator beam will be far from the bandwidth of the actually coupled resonator. For the first time, this finite‐width effect is taken into account. The novelty of this work is the consideration of this finite width effect of coupling beam and cancellation of additional velocity coupling to minimize error in bandwidth estimation. This is achieved by a combination of λ/4 and 3λ/4 coupling beams. In this work, the coupled resonator is modeled using an electrical equivalent circuit.

Silicon photonic microelectromechanical systems add-drop ring resonator in a foundry process

Photonic add-drop filters are crucial components for the implementation of wavelength division multiplexing (WDM) in fiber-optic communication systems. The recent progress in photonic integration has shown the potential to integrate photonic add-drop filters alongside high-performance photonic building blocks on a chip to construct compact and complex photonic-integrated circuits for WDM. Typically, implementations are based on micro-ring resonators with integrated heaters or free carrier dispersion-based modulators to adjust the filter wavelength. However, heaters suffer from high power consumption, and free carriers result in optical absorption losses, limiting the scalability toward very-large-scale circuits. We demonstrate the design, simulation, fabrication, and experimental characterization of a compact add-drop filter based on a vertically movable, MEMS-actuated ring resonator. The MEMS-actuated add-drop filter is implemented in IMEC’s iSiPP50G silicon photonics platform and realized using a short post-processing flow to safely release the suspended MEMS structures in a wafer-level compatible process. The filter exhibits a through port linewidth of ∼1 nm (124.37 GHz) at 1557.1 nm, and it retains a port extinction of 20 dB and a port isolation of >50 dB under 27 V of actuation voltage. The combination of low-power consumption and a compact footprint demonstrates the suitability for very-large-scale integration in photonic circuits.

Resonant Excitation-Induced Nonlinear Mode Coupling in a Microcantilever Resonator

The nonlinear dynamics of microelectromechanical resonators has recently garnered significant attention for their potential use in high-precision detection and information processing. In this paper, we report resonant excitation as a powerful tool for generating nonlinear mode coupling in a cantilever microresonator. It is discovered that resonant driving at its second flexural mode ${f}_{2}$ under moderate driving amplitude gives rise to blue and red sidebands due to mode coupling between the fundamental mode and the second flexural mode. Detuning the driving frequency enables a continuous shift in the frequencies of the blue and red sidebands with a frequency span of 220 Hz. Further increase in the drive amplitude at ${f}_{2}$ mode splitting, and broadband acoustic frequency comb with a frequency span exceeding 500 kHz. Our findings pave the way towards parametric control based on injection locking for manipulating multimode mechanical resonator systems.

Enhanced Sensory Identification in Arrays of Coupled Resonant Sensors

Coupled resonant sensors have been used in a large number of sensing systems with microelectromechanical systems, enabling multi-sensing using single input-output connections as one can record the collective behaviour of an array of coupled resonant sensors using the response of only one of their elements. The forward problem with these systems is to identify the change in eigenvalues recorded when some sensing operation takes place, which often reflects as a eigenvalue perturbation problem. The reverse problem of identifying the sensing element and the sensing amount is challenging, when recording only one readout in such systems. This paper provides a robust new technique to do so with enhanced accuracy and noise tolerance. This is achieved by using properties of eigenpairs and an inverse analysis. The method has been verified using experimental data from an array of coupled microelectromechanical resonators. The technique has also been analysed for potential experimental errors including quantisation and random noises.

Effect of crystal orientation on liquid phase performance of piezoelectric-on-silicon elliptical plate resonators

Various microelectromechanical (MEM) resonator topologies have been proposed for liquid phase sensing applications. Low liquid phase motional resistance (Rm) and moderately high liquid phase quality factor (Q) are critical to the performance of oscillators based on these resonators for real-time frequency tracking in sensing applications. We recently described a new topology we call the elliptical plate resonator EPR that delivers the lowest Rm after normalizing for area (which impacts mass sensitivity as a tradeoff for lower Rm). In this work, we show that further significant gains in performance can be made by choice of device alignment to the silicon crystal axis (< 110 > direction vs. < 100 > direction). We compare the liquid phase performance between the two orientations for a range of geometrical ratios defining the ellipse of the device. We show that the orientation makes a notable difference on trends in liquid phase Q and Rm. By aligning the EPR to the < 110 > direction, we demonstrate a liquid phase Q of 310 and Rm of 2.5 kΩ. Normalizing for area (Rm×A) to express the tradeoff between mass sensitivity and electrical performance in relation to device area, we report an Rm×A of 0.25 kΩ.mm2. We also show that these gains in liquid phase Rm and Q translate into significant lowering of the Allan deviation when these devices are embedded in close loop to track their frequency in real time with water loaded on the device as expected in liquid phase sensing 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.