Fabrication and Energy Harvesting Measurements of Vibrating MEMS Piezoelectric Benders

In this paper, a study is presented in which piezoelectric microbenders were fabricated and tested to demonstrate energy generating performance. Trapezoidal and diagonal (with respect to the substrate crystal directions) unimorph PZT cantilever benders with interdigitated electrode patterns were utilized. The interdigitated design is beneficial for microenergy harvesting devices because it utilizes the $d33$ mode, which can generate higher voltage than the $d31$ mode design. It can also eliminate the bottom electrode by only using an interdigitated top electrode, which facilitates fabrication, as opposed to the $d31$ mode design that requires both top and bottom electrodes. The micro-electromechanical system (MEMS) benders fabricated in this study consist of layers of $SiO2/SiNx/ZrO2/PZT$ and Au/Cr interdigitated electrode on the top. The experimental results indicate that the fundamental frequencies of the microbenders are about 9.1 kHz for the trapezoidal bender and 18.48 kHz for the diagonal bender. The microtrapezoidal bender can generate power of approximately $1.4μW$ into a $680kΩ$ resistive load at the resonant frequency. The diagonal bender can generate power of about $18.2μW$ into a $100kΩ$ resistive load at the resonant frequency.