Structure optimization for efficient AlN piezoelectric energy harvesters

Lead Zirconate Titnate, or PZT, has always been favored over Aluminum Nitride, AlN, in Energy Harvesting applications due to its superior coupling coefficient, d31. However, the use of PZT in some applications, such as medical implants, is not possible due to its toxic nature as it contains Lead. In this paper, a comparison between the performances of PZT and AlN harvesters is held by utilizing the same uniform cantilever structure. The results of this comparison show that PZT has only 4 times the output power of AlN, and 33% lower resonance frequency. To further increase the output power of the AlN harvester and drive its resonance frequency down to perform PZT-like, a modification to the beam structure is proposed. The modification is to taper the cross-section of the beam linearly. The new structure has the same exact area as the uniform cantilever beam. The FEM simulation results show that the output power of the AlN harvester with the modified structure is nearly the same as the uniform PZT structure, around 1.3 μW for an input acceleration of 0.5g and the resonance frequency is even 35% lower. The gap in performance between PZT and AlN is nearly eliminated using the proposed structure without requiring extra area.