# Enhanced electromechanical coupling in piezoelectric MEMS vibration energy harvesters via strain-induced phase transition in Mn-doped bismuth ferrite epitaxial films

## TL;DR

This paper shows how adding Mn to bismuth ferrite films improves their piezoelectric properties, making them better for energy harvesting devices.

## Contribution

The study introduces a strain-induced phase transition in Mn-doped bismuth ferrite films that significantly enhances electromechanical coupling in MEMS energy harvesters.

## Key findings

- BFMO films showed a high transverse piezoelectric coefficient of –6.0 C/m².
- The films exhibited a fivefold increase in electromechanical coupling factor compared to BFO films.
- Structural analysis confirmed a phase transition from rhombohedral to monoclinic structures.

## Abstract

Mn-doped BiFeO3 (BFMO) epitaxial films grown on (100) Si wafers delivered enhanced electrical and piezoelectric properties under systematically optimized growth conditions, realized through a biaxial combinatorial sputtering method. The dielectric constant and dielectric loss of the resulting BFMO films were approximately 140 and 1%, respectively, considerably lower than those of undoped BiFeO3. Most notably, the effective transverse piezoelectric coefficient was –6.0 C/m2, the highest yet reported for this material system. According to detailed structural and electrical characterizations, the improved piezoelectric performance stems from a strain-induced phase transition from the rhombohedral to the monoclinic structure. To demonstrate this enhancement beyond the material level, the optimized films were successfully integrated into piezoelectric MEMS vibration-energy harvesters. The films demonstrated device-level performance improvements with a generalized electromechanical coupling factor \documentclass[12pt]{minimal}
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