MEMS accelerometers are widely used devices, second only to pressure sensors. While traditionally used for vibration monitoring and inertial navigation, applications are expanding to health monitoring and implantable devices. Piezoelectric MEMS accelerometers offer advantages over piezoresistive and capacitive types, including higher temperature stability, robustness, and sensitivity. However, high-performance piezoelectric materials like PZT raise environmental concerns due to heavy metals, while lead-free alternatives have their own sustainability challenges. The use of poly(vinylidene fluoride) (PVDF) offers a solution: it has higher piezoelectric coefficients than some environmentally friendly alternatives like ZnO and AIN, and it enables simpler fabrication flows using techniques like laser micromachining and additive manufacturing. This research addresses the lack of mature research on high-performance polymeric piezoelectric MEMS accelerometers, specifically focusing on conventional accelerometers (as opposed to energy harvesters) to overcome bandwidth limitations. The paper proposes a new design for PVDF-based piezoelectric MEMS accelerometers, fabricates three samples using a simplified microfabrication technology, and characterizes their performance.

The paper reviews the existing literature on MEMS accelerometers, highlighting the advantages and disadvantages of different coupling principles (capacitive, piezoresistive, piezoelectric). It discusses the environmental concerns associated with traditional piezoelectric materials (PZT, KNN) and the limitations of more environmentally friendly alternatives (AIN, ZnO). The literature review emphasizes the potential of PVDF as a suitable piezoelectric material for MEMS accelerometers due to its higher piezoelectric coefficients and compatibility with advanced fabrication methods. It also notes the relative lack of research on high-performance polymeric piezoelectric MEMS accelerometers designed for conventional operation (as opposed to energy harvesting applications).

The study proposes a novel design for a PVDF-based piezoelectric MEMS accelerometer. The design incorporates six identical cantilever-based sensing units connected in parallel to increase reliability and magnify the effect of performance optimization. The design utilizes a 100 µm thick PVDF layer for optimal sensitivity, a 75 µm thick polyimide layer for structural stability, and 3D-printed inertial mass. A simplified fabrication process is employed, involving laser micromachining of thin films and 3D stereolithography. The fabrication process bypasses traditional micromachining steps, reducing complexity. Three samples were fabricated and characterized for mechanical resonance behavior, frequency response, sensitivity, and noise density. Finite element analysis (FEA) using COMSOL was employed to simulate the device's fundamental resonant frequency and stress conditions under acceleration. Experimental characterization involved measuring the mechanical resonance behavior and evaluating the performance as an accelerometer.

The fabricated PVDF-based MEMS accelerometer demonstrated a sensitivity of 21.82 pC/g (equivalent open-circuit voltage sensitivity: 126.32 mV/g), a 5% flat band of 58.5 Hz, and a noise density of 6.02 µg/v/Hz. These results are comparable to state-of-the-art PZT-based accelerometers and surpass the performance of several commercial MEMS accelerometers. The device’s small area (10 times smaller) and wide flat band (4 times larger) compared to previous organic piezoelectric MEMS accelerometers are significant advantages. The theoretical feasibility of the design is supported by equations describing piezoelectric sensing, stress, and bending in response to mechanical input. The simulation results, including the fundamental resonant frequency (126.46 Hz) and stress distribution under acceleration, align well with theoretical predictions and experimental measurements. Optical images of the fabricated samples demonstrate the successful implementation of the proposed fabrication flow.

The achieved performance metrics demonstrate the potential of PVDF-based piezoelectric MEMS accelerometers as a viable alternative to traditional PZT-based devices. The superior performance coupled with the simplified and environmentally friendly fabrication process addresses critical limitations of existing technologies. The significantly smaller device area opens possibilities for miniaturized applications. The results validate the theoretical analysis and design choices, showing that a thicker PVDF layer contributes to higher sensitivity. The use of a simplified fabrication flow reduces manufacturing complexity and cost while promoting sustainability. This research makes a substantial contribution to the field of polymeric MEMS devices and specifically advances the development of fully organic inertial sensing microsystems.

This study successfully demonstrated a high-performance PVDF-based piezoelectric MEMS accelerometer with significantly improved characteristics compared to existing organic alternatives. The simplified fabrication process offers advantages in terms of cost, time, and environmental impact. Future work could explore further optimization of the device design and fabrication process to enhance performance and expand applications in fields such as flexible electronics and implantable sensors.

The study only fabricated and characterized three samples, limiting the statistical power of the results. Further testing with a larger number of samples is needed to confirm the reproducibility and robustness of the findings. The long-term stability and reliability of the device under various environmental conditions have not been fully investigated and should be explored in future studies.