VIBRATION ENERGY HARVESTERS OF LEAD-FREE (K,Na)NbO3 PIEZOELECTRIC THIN FILMS

In this study, we fabricated piezoelectric energy harvesters composed of lead-free (K,Na)NbO3 (KNN) thin films and compared the power generation performance with PZT-thin film energy harvesters. Both of the piezoelectric thin films were deposited on Pt/Ti/Si cantilevers by rf-sputtering. The KNN and PZT thin films had perovskite structure, and showed the relative dielectric constants of 744 and 872, respectively. The transverse piezoelectric properties were evaluated from the inverse piezoelectric effect and both films showed the almost the same e31,f of −11 C/m. The performance of the power generation was measured for the simple unimorph cantilevers of KNN/Si and PZT/Si. The averaged output power of KNN and PZT thin-film reached 1.1 μW and 1.0 μW, respectively. Generalized electromechanical coupling factors (GEMC) of KNN/Si and PZT/Si energy harvesters were calculated to be 1.7×10 and 0.65×10, respectively. These results suggest that the lead-free KNN films have comparable or better performance than PZT thin films in the application of MEMS energy harvest.