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1. MEMS Acoustic Emission Sensors

   https://doi.org/10.3390/app10248966  

   Ozevin, Didem (December 2020, Applied Sciences)

   null (Ed.)

   This paper presents a review of state-of-the-art micro-electro-mechanical-systems (MEMS) acoustic emission (AE) sensors. MEMS AE sensors are designed to detect active defects in materials with the transduction mechanisms of piezoresistivity, capacitance or piezoelectricity. The majority of MEMS AE sensors are designed as resonators to improve the signal-to-noise ratio. The fundamental design variables of MEMS AE sensors include resonant frequency, bandwidth/quality factor and sensitivity. Micromachining methods have the flexibility to tune the sensor frequency to a particular range, which is important, as the frequency of AE signal depends on defect modes, constitutive properties and structural composition. This paper summarizes the properties of MEMS AE sensors, their design specifications and applications for detecting the simulated and real AE sources and discusses the future outlook. 

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2. A Programmable CMOS Feedback IC for Reconfigurable MEMS-Referenced Oscillators

   Khanmohammad, H.; Wang, P.; Babecki, C.; Feng, P. X.-L.; Mandal, S. (June 2016, New Circuits and Systems Conference (NEWCAS), 2016 IEEE 14th International)

   MEMS resonators integrated with CMOS feedback networks have a potentially wide field of applications as oscillator circuits in communications and sensor systems. However, considerable advancements to this nascent technology are required to realize such a vision. We present a configurable CMOS chip which facilitates the development of MEMS-referenced oscillators, especially for timing and sensing applications in harsh environments. The chip has been designed in the OnSemi 3M2P 0.5 um process. It supports MEMS resonators with various frequencies (10–120 kHz), resonant modes, and impedance levels, thus allowing interfacing to a wide range of devices. This paper describes analysis, design, and simulation results. 

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

   https://doi.org/10.1038/s41467-023-36936-9  

   Lee, Daehun; Jahanbani, Shahin; Kramer, Jack; Lu, Ruochen; Lai, Keji (March 2023, Nature Communications)

   Abstract 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. 

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5. 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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