Micro-fabricated flexible PZT cantilever using d33 mode for energy harvesting
© The Author(s) 2017
Received: 7 December 2016
Accepted: 29 March 2017
Published: 4 April 2017
This paper presents a micro-fabricated flexible and curled PZT [Pb(Zr0.52Ti0.48)O3] cantilever using d33 piezoelectric mode for vibration based energy harvesting applications. The proposed cantilever based energy harvester consists of polyimide, PZT thin film, and inter-digitated IrOx electrodes. The flexible cantilever was formed using bulk-micromachining on a silicon wafer to integrate it with ICs. The d33 piezoelectric mode was applied to achieve a large output voltage by using inter-digitated electrodes, and the PZT thin film on polyimide layer has a remnant polarization and coercive filed of approximately 2P r = 47.9 μC/cm2 and 2E c = 78.8 kV/cm, respectively. The relative dielectric constant was 900. The fabricated micro-electromechanical systems energy harvester generated output voltages of 1.2 V and output power of 117 nW at its optimal resistive load of 6.6 MΩ from its resonant frequency of 97.8 Hz with an acceleration of 5 m/s2.
Vibration-based energy harvesters have been considered as a promising power solution for wireless sensor nodes due to their sustainability and reliability in harsh environments and because vibration energy has a higher power density than other forms of wasted energy. Especially, piezoelectric energy harvesters have been actively studied due to their easy integration with micro-electromechanical systems (MEMS) and integrated circuit (IC) technologies [1–3]. In a typical piezoelectric energy harvester, a piezoelectric material is attached to a rigid structure, such as a silicon cantilever, and a proof mass located at the free end of the cantilever is coupled with an induced vibration. The transducer combined with a mechanical resonator converts the kinetic energy of the proof mass to electrical energy via the piezoelectric material [3–7]. However, the typical rigid-body based cantilever type energy harvester has a large resonance frequency due to its high spring constant. Thus, it is not for harvesting energy from human activity or low frequency ambient vibration. Polyvinylidene fluoride (PVDF) is probably the most popular material for flexible energy harvesting applications. However, PVDF has lower dielectric and piezoelectric properties than ceramics such as PZT. For flexible piezoelectric films based on ceramics, several approaches have been reported. Nunes-Pereira et al. reported a piezoelectric fiber composite based flexible energy harvester for wearable applications. Piezoelectric fiber composite (PFC) based devices presented a larger output than PVDF based ones . Lin et al. presented a ZnO nano wire array based flexible nano generator by employing polydimethylsiloxane (PDMS) . Do et al. and Park et al. also demonstrated a ceramic based flexible piezoelectric film. The laser annealing lift-off technique was utilized to transform the piezoelectric ceramic layer into a flexible substrate [10, 11]. Although the feasibility of using flexible piezoelectric films for energy harvesting applications has been well established, the fabrication process has limitations in terms of its integration with integrated circuits (ICs), such as the rectifying or boost-up converter in the interface circuit of the energy harvester. In this paper, a flexible piezoelectric energy harvester has been proposed and developed using low temperature process and silicon bulk micromachining technique for the formation of proof mass to compatible with integrated circuit fabrication process without any complex fabrication process such as laser annealing lift-off process. The proposed harvester also utilized a polyimide based flexible cantilever with low spring constant for harvesting energy from human activity or low frequency ambient vibrations.
Design and fabrication
Experimental results and discussion
A flexible PZT cantilever operating in d33 piezoelectric mode with an inertial mass located at its free end was presented for energy harvesting applications. The proposed energy harvester was fabricated using a multi-layered polyimide/PZT cantilever and bulk-micromachining. The fabricated PZT cantilever is flexible and generates electricity from low frequency vibration by using an inter-digitated electrode for d33 piezoelectric mode. The thin polyimide film used for the elastic layer of the cantilever layer was highly effective because of its flexibility and ability to lower the resonant frequency of the harvesting device. In addition, the proposed process is applicable to mass-production and integration with ICs, unlike the previously reported ceramic based flexible PZT films.
HO participated in the design and fabrication of the piezoelectric energy harvester in this study. JC participated in the design and measurement of the study. JY conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
This work was supported by Basic Science Research Program (2013R1A1A2A10064810) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology, Korea.
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