High Power Density CMOS Compatible Micro-Machined MEMs Energy Harvester

Optimization of piezoelectric energy harvester (PEH) to convert the ambient vibrational energy into maximum electrical energy has been of continued interest. The integration of the proof mass with the optimum cantilever width significantly enhances the output power of PEH. In this paper, we propose an optimized design of PEH that outperforms the existing AlN-based design in terms of power density. We analytically optimize the design of: 1) cantilever-to-harvester length and 2) cantilever-to-harvester width (proof mass width) ratios for the maximum output power. The optimized harvester is fabricated using a novel integration scheme for the bottom electrode with Au as an interlayer. The Au interlayer is used to grow a good quality of AlN film with piezoelectric coefficients, d
₃₃
= 12 pm/V and d
₃₁
= -2.37 pm/V. It is found that in order to achieve the optimum output from PEH, the fractional length and width occupied by cantilever are 28%-40% and 38%-45%, respectively. The optimized designs are fabricated using a CMOS compatible process. The maximum power density measured from the fabricated PEHs is found to be 9.36 μW/mm
³
, which is better than the similar reported data. The optimized and compact low-power PEHs reported in this paper have high potential to be integrated with the system on chip (SOC) and other wireless sensor applications.