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1. A review on temperature coefficient of frequency (TC f ) in resonant microelectromechanical systems (MEMS)

   https://doi.org/10.1063/5.0201566  

   Sui, Wen; Pearton, Stephen J; Feng, Philip X-L (June 2025, Applied Physics Reviews)

   Microelectromechanical systems (MEMS) have emerged as highly attractive alternatives to conventional commercial off-the-shelf electronic sensors and systems due to their ability to offer miniature size, reduced weight, and low power consumption (i.e., SWaP advantages). These features make MEMS particularly appealing for a wide range of critical applications, including communication, biomedical, automotive, aerospace, and defense sectors. Resonant MEMS play crucial roles in these applications by providing precise timing references and channel selections for electronic devices, facilitating accurate filtering, mixing, synchronization, and tracking via their high stability and low phase noise. Additionally, they serve as key components in sensing applications, enabling detection and precise measurement of physical quantities for monitoring and control purposes across various fields. Temperature stability stands as a paramount performance specification for MEMS resonators and oscillators. It relates to the responsivity of a resonator's frequency to temperature variations and is typically quantified by the temperature coefficient of frequency (TCf). A constant and substantially large absolute TCf is preferred in MEMS temperature sensing applications, while a near-zero TCf is required for timing and other MEMS transducers that necessitate the decoupling of temperature effects on the resonance frequency. This comprehensive review aims to provide an in-depth overview of recent advancements in studying TCf in MEMS resonators. The review explores the compensation and engineering techniques employed across a range of resonator types, utilizing diverse materials. Various aspects are covered, including the design of MEMS resonators, theoretical analysis of TCf, temperature regulation techniques, and the metallization effect at high temperatures. The discussion encompasses TCf analysis of MEMS resonators operating in flexural, torsional, surface, and bulk modes, employing materials such as silicon (Si), lithium niobate (LiNbO3), silicon carbide (SiC), aluminum nitride (AlN), and gallium nitride (GaN). Furthermore, the review identifies areas that require continued development to fully exploit the TCf of MEMS resonators. 

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2. Interface Material Modification to Enhance the Performance of a Thin-Film Piezoelectric-on-Silicon (TPoS) MEMS Resonator by Localized Annealing Through Joule Heating

   https://doi.org/10.3390/mi16080885  

   Zaman, Adnan; Guneroglu, Ugur; Alsolami, Abdulrahman; Li, Liguan; Wang, Jing (August 2025, Micromachines)

   This paper presents a novel approach employing localized annealing through Joule heating to enhance the performance of Thin-Film Piezoelectric-on-Silicon (TPoS) MEMS resonators that are crucial for applications in sensing, energy harvesting, frequency filtering, and timing control. Despite recent advancements, piezoelectric MEMS resonators still suffer from anchor-related energy losses and limited quality factors (Qs), posing significant challenges for high-performance applications. This study investigates interface modification to boost the quality factor (Q) and reduce the motional resistance, thus improving the electromechanical coupling coefficient and reducing insertion loss. To balance the trade-off between device miniaturization and performance, this work uniquely applies DC current-induced localized annealing to TPoS MEMS resonators, facilitating metal diffusion at the interface. This process results in the formation of platinum silicide, modifying the resonator’s stiffness and density, consequently enhancing the acoustic velocity and mitigating the side-supporting anchor-related energy dissipations. Experimental results demonstrate a Q-factor enhancement of over 300% (from 916 to 3632) and a reduction in insertion loss by more than 14 dB, underscoring the efficacy of this method for reducing anchor-related dissipations due to the highest annealing temperature at the anchors. The findings not only confirm the feasibility of Joule heating for interface modifications in MEMS resonators but also set a foundation for advancements of this post-fabrication thermal treatment technology. 

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3. 2D Au-Coated Resonant MEMS Scanner for NIR Fluorescence Intraoperative Confocal Microscope

   https://doi.org/10.3390/mi10050295  

   Yao, Cheng-You; Li, Bo; Qiu, Zhen (May 2019, Micromachines)

   The electrostatic MEMS scanner plays an important role in the miniaturization of the microscopic imaging system. We have developed a new two-dimensional (2D) parametrically-resonant MEMS scanner with patterned Au coating (>90% reflectivity at an NIR 785-nm wavelength), for a near-infrared (NIR) fluorescence intraoperative confocal microscopic imaging system with a compact form factor. A silicon-on-insulator (SOI)-wafer based dicing-free microfabrication process has been developed for mass-production with high yield. Based on an in-plane comb-drive configuration, the resonant MEMS scanner performs 2D Lissajous pattern scanning with a large mechanical scanning angle (MSA, ±4°) on each axis at low driving voltage (36 V). A large field-of-view (FOV) has been achieved by using a post-objective scanning architecture of the confocal microscope. We have integrated the new MEMS scanner into a custom-made NIR fluorescence intraoperative confocal microscope with an outer diameter of 5.5 mm at its distal-end. Axial scanning has been achieved by using a piezoelectric actuator-based driving mechanism. We have successfully demonstrated ex vivo 2D imaging on human tissue specimens with up to five frames/s. The 2D resonant MEMS scanner can potentially be utilized for many applications, including multiphoton microendoscopy and wide-field endoscopy. 

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4. A Battery-Less Wireless Respiratory Sensor Using Micro-Machined Thin-Film Piezoelectric Resonators

   https://doi.org/10.3390/mi12040363  

   Moradian, Sina; Akhkandi, Parvin; Huang, Junyi; Gong, Xun; Abdolvand, Reza (April 2021, Micromachines)

   In this work, we present a battery-less wireless Micro-Electro-Mechanical (MEMS)-based respiration sensor capable of measuring the respiration profile of a human subject from up to 2 m distance from the transceiver unit for a mean excitation power of 80 µW and a measured SNR of 124.8 dB at 0.5 m measurement distance. The sensor with a footprint of ~10 cm2 is designed to be inexpensive, maximize user mobility, and cater to applications where disposability is desirable to minimize the sanitation burden. The sensing system is composed of a custom UHF RFID antenna, a low-loss piezoelectric MEMS resonator with two modes within the frequency range of interest, and a base transceiver unit. The difference in temperature and moisture content of inhaled and exhaled air modulates the resonance frequency of the MEMS resonator which in turn is used to monitor respiration. To detect changes in the resonance frequency of the MEMS devices, the sensor is excited by a pulsed sinusoidal signal received through an external antenna directly coupled to the device. The signal reflected from the device through the antenna is then analyzed via Fast Fourier Transform (FFT) to extract and monitor the resonance frequency of the resonator. By tracking the resonance frequency over time, the respiration profile of a patient is tracked. A compensation method for the removal of motion-induced artifacts and drift is proposed and implemented using the difference in the resonance frequency of two resonance modes of the same resonator. 

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5. Snap-Through and Mechanical Strain Analysis of a MEMS Bistable Vibration Energy Harvester

   https://doi.org/10.1155/2019/6743676  

   Derakhshani, Masoud; Berfield, Thomas A. (March 2019, Shock and Vibration)

   Vibration-based energy harvesting via microelectromechanical system- (MEMS-) scale devices presents numerous challenges due to difficulties in maximizing power output at low driving frequencies. This work investigates the performance of a uniquely designed microscale bistable vibration energy harvester featuring a central buckled beam coated with a piezoelectric layer. In this design, the central beam is pinned at its midpoint by using a torsional rod, which in turn is connected to two cantilever arms designed to induce bistable motion of the central buckled beam. The ability to induce switching between stable states is a critical strategy for boosting power output of MEMS. This study presents the formulation of a model to analyze the static and dynamic behaviors of the coupled structure, with a focus on the evolution of elongation strain within the piezoelectric layer. Cases of various initial buckling stress levels, driving frequencies, and driving amplitude were considered to identify regimes of viable energy harvesting. Results showed that bistable-state switching, or snap-through motion of the buckled beam, produced a significant increase in power production potential over a range of driving frequencies. These results indicate that optimal vibration scavenging requires an approach that balances the initial buckling stress level with the expected range of driving frequencies for a particular environment. 

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