High efficiency piezoelectric MEMS vibrational energy harvsters using (100) oriented BIFEO3 films

We have developed a design principle to fabricate of high efficient piezoelectric MEMS vibrational energy harvesters (pVEHs) from the viewpoints of materials science and MEMS. Based on the principle, we propose BiFeO ₃ films as the piezoelectric films, because it is lead free ferroelectric and has potential for high electromechanical coupling factor (k ₃₁ , f ² ). To maximize the conversion efficiency of pVEHs, the microstructure and thickness of BiFeO ₃ films were optimized. As the result, (100) oriented 1.75-μm-thick-BiFeO ₃ films with the e _{31, f} piezoelectric coefficient of -2.5 C/m ² was obtained on Si substrate. The pVEHs using the BiFeO ₃ films showed the mechanical quality factor of around 400 and normalized output power of 0.9 μW/mm ² /G ² .