Research On Dual-crystal Cantilever Piezoelectric MEMS Vibration Energy Harvester

With the rapid development of micro-machining,microelectronics and wireless sensor technology,wireless sensor network(WSN)has been widely used in all walks of life.The small-sized and low-power consumpting wireless sensor,as a basic component of WSN,usually powered by electrochemical batteries,has some defects such as short service life,periodic replacement and environmental pollution.Therefore,the sustainable piezoelectric energy harvesters as power supply components with longer life span have been widely studied.Aiming at solving the problems of poor structural stability,low energy conversion efficiency and high operating frequency of micro piezoelectric energy harvester,the author proposes a micro energy harvester based on piezoelectric bimorph thick film in this paper.The structural parameters of the device are optimized.Based on the fabrication of bicrystal piezoelectric thick film by bonding and thinning technology,an experimental prototype is fabricated by MEMS technology such as coating and lithography.The main work of this paper is as follows:(1)A piezoelectric MEMS energy harvester with cantilever structure based on piezoelectric bimorph thick film is proposed.Based on the analysis of structure type,material selection and working mode,combined with the actual preparation process,three kinds of piezoelectric cantilever energy harvester structures,namely traditional rectangular beam,digging hole rectangular beam and trapezoidal beam,were designed with PZT material as the upper and lower piezoelectric functional layers and phosphor bronze as the substrate.The theoretical models of rectangular and trapezoidal piezoelectric structure devices were established.(2)The finite element model of piezoelectric vibration energy harvester was established with the help of the finite element software COMSOL.In the paper were analyzed the effects of the length of cantilever beam,PZT thickness,mass block size,the size and location of rectangular beam hole as well as the influence of trapezoidal beam size and other parameters on resonant frequency and output power of the system.The corresponding device structure optimization parameters were obtained.(3)The fabrication methods of piezoelectric bimorph thick film and the MEMS fabrication methods of energy harvesters as well as the producing processes were studied.The preparation technology of piezoelectric bimorph thick film was studied based on bonding and thinning technology,which means the realization of bonding between PZT and phosphor bronze substrate by conductive epoxy resin as the intermediate bonding layer,and the realization of thinning PZT bulk material by mechanical polishing method;Also studied in the paper was the the MEMS processing technology of piezoelectric energy harvester,such as lithography,sputtering,etching,laser cutting.A discussions was given on the specific process parameters.Finally,according to the design process,three kinds of piezoelectric MEMS energy harvester prototype were prepared.(4)The output performance of three kinds of experimental prototypes was tested by vibration energy collector test system.The experimental results showed that the output performance of the bimorph rectangular beam piezoelectric device and the trapezoidal beam piezoelectric device was better than that of the rectangular beam piezoelectric device.When the external excitation acceleration was 3.5g,the load voltage of the bimorph rectangular piezoelectric device was89.7HZ? 32.8v and the output power was 0.784mw;the load voltage of the BICRYSTAL rectangular beam piezoelectric device was 60.4HZ?42V and the output power was 1.0587mw;the load voltage of the output power of the bimorph trapezoidal beam piezoelectric device was 76.8HZ?36.6v while the output power was 0.9053 mw.(5)Application test experiments were carried out to the device.The capacitance charging experiment is carried out by using rectangular beam piezoelectric vibration energy collector,the results of which showed that under the condition of 2g vibration acceleration and when the 100 ?F and 220 ?F capacitor was charged,the capacitor voltage could reach 9.6V and 8.5V in 60 s and 110 s respectively.The power supply tests of temperature sensor and wireless sensor module were carried out by using the prototype of rectangular and trapezoidal devices with holes.The results showed that the devices could effectively supply power to the sensor and proved its potential application in practice.