Aim of the project
Energy harvesting using piezoelectric materials has gained tremendous attention in the past decade for running low-powered electronics. It provides a remote source of electricity from waste vibrations with a myriad of applications, for instance pressure sensors inside car tires or other environmental sensors at remote locations like airplane wings and wind-turbine air blades. In a report by IDTechEx it has been established that piezoelectric energy harvesting investments will grow to $145m in 2018. Thereafter, it will create a $667m market by 2022. (www.idtechex.com)
State-of-the-art EH performance with a figure of merit (FOM) as high as 50 GPa is based on a Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) piezoelectric layer on silicon using a buffer layer of SrTiO3 (STO) and a SrRuO3 bottom electrode. This high FOM is obtained for a hetero-epitaxially grown structure with extraordinary crystal-quality of all the layers, which is extremely difficult to achieve since an intimate contact between the oxides and silicon is intrinsically instable. The problem has been overcome using molecular beam epitaxy (MBE) with a very delicate growth sequence. The method is unfortunately inappropriate for industrial fabrication, mainly due to extremely slow growth rates and the instability of the process itself. The main objective in this project is thus to use another industrially acceptable technology for growing epitaxial layers of piezoelectric material on silicon with the quality needed for reaching a high FOM for EH. Pulsed laser deposition (PLD) is an alternative method for the high-speed/high-quality growth of thin films and has high potential to successfully solve MBE-related drawbacks by engineering the silicon-oxide interface. The selection of PLD as a thin-film growth method is due to the combination of required growth control and the availability of a commercial large-area tool for device fabrication. The buffered silicon is covered with a corresponding bottom electrode and functionalized with PMN-PT layers for devices that require higher energy densities. Alternatively, PMN-PT films are being grown using aerosol deposition, which proved to be successful for the rapid fabrication of Pb(Zr,Ti)O3 films for EH applications. Within the scope of the project, both small-area and large-area systems are being used, with up-scaling up to 6-inch wafers. The latter is brought about by the PiezoFlare 1200 system, which is the first automated PLD system in the world installed at SINTEF in 2012-2013. Considering the electromechanical response of as-grown heterostructures micro-electromechanical (MEM) transducers are being designed and fabricated using standard MEMS fabrication processes in the Stiftelsen SINTEF piezoMEMS competence centre (www.piezomicrosystems.com) and the National Taiwan University NEMS center (nems.ntu.edu.tw) and tested at the Jožef Stefan Institute. The energy extraction interfacing circuit of the EH devices will be optimized and studied, and then tested on real environmental systems. In the final stage of the project the EH device will be integrated with a remote sensor and validated on the device level, while on each step of the project commercialization of the development will be considered.