A piezoelectric micro-energy harvester for nanosensors

A novel piezoelectric micro-energy generator is presented, which converts the mechanical vibrations into electricity by utilizing the piezoelectric effect of zinc oxide nanowires (ZnO NW). This is the first time an integrated energy harvester is built where vertically standing NWs are directly coupled to a MEMS proof-mass for maximum conversion of the vibration energy while maintaining the size in the order of hundreds of micrometers. Hydrothermal growth of nanowires combined with MEMS surface micromachining technology and LIGA is employed to fabricate the device. Patterned SU-8 photoresist confines the growth area of the NW block, located between the silicon substrate and a suspended silicon nitride membrane, on which a nickel proof-mass is electroplated. A piezoelectric potential between the two ends of the NW block is formed once compressed by the membrane due to external vibration. A maximum power of 42 pW across 5.5 MΩ load is measured at the vibration frequency of 40 Hz with an acceleration of 1.4g. The corresponding output voltage is 14.7 mV.