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In the modern field of microelectronics and advanced sensing, Micro-ElectroMechanical Systems (MEMS) represent a mature yet dynamic platform for the development of high-performance miniaturized devices, thanks to their ability to integrate transduction, actuation, and readout in compact, low-power devices compatible with wafer-level processing. Resonant MEMS strain sensors convert small strain variations into electrical signals starting from a mechanical resonance frequency shift, enabling high-resolution monitoring of several parameters connected to strain variations in collaborative robotics, predictive maintenance, and structural health monitoring. Based on the mechanical resonance of an elastic structure, they detect changes in the applied strain that produce a shift of the resonance frequency. Since the frequency variation is proportional to the applied strain, the resonator can be calibrated as a strain sensor: an increase in frequency indicates tensile strain, whereas a decrease indicates compressive strain.
To achieve high performance in strain-sensing applications based on mechanical resonators, a high strain sensitivity S is essential, as it represents the proportionality factor between the resonance frequency shift and the applied strain. The resonator’s quality factor Q is also crucial, since these devices are typically operated in closed-loop configurations, such as MEMS oscillators or phase-locked loop (PLL) circuits [1]. In this context, the frequency stability of the system is strongly influenced by the resonator Q factor, with higher values generally leading to improved stability, and consequently to lower output noise on the sensor.
Within the European FET Project “SiC Nano for PicoGeo”, the development of micromechanical resonators fabricated from cubic silicon carbide (3C-SiC) grown on silicon by wafer-level micromachining techniques, including vacuum encapsulation, was carried out, achieving very high Q-factors [2] and strain sensitivity on the manufactured prototypes. By employing a different design strategy based on stress-engineered poly-Si/SiC double-clamped beam resonators, it was also possible to improve and control both the mechanical resonance frequency and the sensitivity of the resonators [3].
Despite the demonstrated performance, several scientific challenges remain open. In particular, the development of dedicated control electronics is essential to optimize the bandwidth–resolution trade-off while preserving high readout stability and device robustness under realistic operating conditions.
Another promising avenue is the extension of this technology to ultra-high-bandwidth force and torque sensors for robotic applications. This growing market imposes stringent requirements in terms of response speed, measurement accuracy, and long-term reliability.
Furthermore, in a context of future technology transfer, the scalability of the proposed solution toward industrial applications, such as industrial automation and automotive systems, will need to be thoroughly evaluated, as cost, integration, and long-term reliability become critical requirements in these domains.
[1] Belsito L., et al. “Nanostrain Resolution Strain Sensing by Monocrystalline 3C-SiC on SOI Electrostatic MEMS Resonators”. J. Microelectromech. Syst. 2020, 29, 117 – 128.
[2] Sapienza S., et al. "Fabrication of Wafer-Level Vacuum-Packaged 3C-SiC Resonant Microstructures Grown on< 111> and< 100> Silicon". Key Engineering Materials 2024, 984, 29-33.
[3] Sapienza S., et al. "Fabrication of Wafer-Level Vacuum Packaged Poly-SI/SiC Beam Resonators with Strain Sensitivity Larger than 1 kHz/με". Transducers 2025, 1572-1575.
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