Piezoelectric MEMS already support miniature sensors, actuators, and energy harvesters, but material limitations continue to constrain performance. PZT-based films offer strong piezoelectricity, while AlN-based films provide low permittivity and high quality factors; however, neither fully satisfies the growing need for highly sensitive, ultra-compact devices in dense sensor arrays and AI-enabled systems. Bismuth ferrite has emerged as a promising lead-free alternative, yet improving its performance on silicon has remained difficult because films on Si experience tensile strain rather than the compressive strain commonly studied on oxide single crystals. Based on these challenges, in-depth research is needed on high-performance lead-free piezoelectric films compatible with silicon MEMS platforms.
Researchers from Osaka Metropolitan University and the Osaka Research Institute of Industrial Science and Technology reported (DOI: 10.1038/s41378-026-01177-5) the study in Microsystems & Nanoengineering after the paper was accepted on January 4, 2026. The team showed that Mn-doped bismuth ferrite epitaxial films grown on silicon can undergo a strain-induced transition from a rhombohedral to a monoclinic phase, significantly strengthening piezoelectric behavior and improving the performance of MEMS vibration energy harvesters fabricated from the material.
To identify the best film conditions, the researchers used a biaxial combinatorial sputtering method that created controlled gradients in temperature and composition across a wafer. They then mapped crystal structure, electrical response, and piezoelectric performance. The optimized Mn-doped films showed a dielectric constant of about 140 and dielectric loss of about 1%, both favorable for microelectromechanical systems (MEMS) use. Most importantly, the effective transverse piezoelectric coefficient reached –6.0 C/m², the highest reported so far for this material system. Structural analysis showed that the gain came from a strain-induced rhombohedral-to-monoclinic phase transition on silicon. When the films were built into MEMS harvesters, the devices achieved a generalized electromechanical coupling factor (K²) of 0.5%, about five times that of comparable undoped BFO devices. Their K²Qm value reached 2.7, nearly three times higher than the earlier undoped design, and the device generated over 90% of its theoretical maximum output under resonant conditions. Under impulsive excitation, the BFMO device also damped faster than the BFO device, making it better suited for frequency-up conversion under irregular real-world vibrations.
The study shows that carefully controlling phase stability on silicon can translate directly into better MEMS performance. Rather than improving a material property in isolation, the researchers linked crystal-level engineering to measurable gains in device efficiency and response. That connection is especially important for practical microsystems, where fabrication compatibility, electrical behavior, and energy conversion must work together in a single platform.
The findings may support the next generation of self-powered microsystems, compact sensors, and distributed intelligent electronics. A lead-free film that combines strong piezoelectric response, relatively low permittivity, and silicon compatibility could be especially valuable in environments with weak, broadband, or unpredictable vibrations. The authors note that further optimization of MEMS fabrication, particularly reducing plasma-related film damage, could preserve even more of the material’s intrinsic performance. With that progress, the approach may open a scalable path toward batch-manufactured MEMS devices that are smaller, cleaner, and more energy efficient.
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References
DOI
10.1038/s41378-026-01177-5
Original Source URL
https://doi.org/10.1038/s41378-026-01177-5
Funding Information
This study was supported by the Japan Science and Technology Agency as part of Core Research for Evolutional Science and Technology (CREST; grant No. JPMJCR20Q2) and Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE; grant No. JPMJAP2312). During manuscript preparation, S.A. was hosted as a visiting scholar in Prof. Susan Trolier-McKinstry's group at The Pennsylvania State University, with support from the ASPIRE program.
About Microsystems & Nanoengineering
Microsystems & Nanoengineering is an online-only, open access international journal devoted to publishing original research results and reviews on all aspects of Micro and Nano Electro Mechanical Systems from fundamental to applied research. The journal is published by Springer Nature in partnership with the Aerospace Information Research Institute, Chinese Academy of Sciences, supported by the State Key Laboratory of Transducer Technology.