Energy micro-harvesters for powering up sensors and portable microsystems
The project will develop a piezoelectric micro-harvester (a MEMS structure covered with a thin piezoelectric film with the purpose to convert the mechanical energy into electrical energy – the direct piezoelectric effect). It will contain doped PZT (with high piezoelectric coefficients) as thin films on Si substrate. The project will also provide the design and fabrication of the energy storage device and the associated circuitry.
The main purpose is to develop new techniques for harvesting the energy from the environment (mechanical vibrations with various frequencies) in the 1-100µW domain, to open the possibility for autonomous operation of portable devices and systems used in aeronautics or in civil applications. The main target of the project is to develop and improve this technology for excluding the use of chemical bateries or complex cabling within microsensors / microsystems, therefore increasing the sensors, complex systems and networks autonomy.
The micro-harvester will include multiple MEMS cantilevers covered with thin piezoelectric PZT films, connected together for increasing the power density.
Conversion of the mechanical energy in the environment into electrical energy
Concept of the energy micro-harvester, integrated with the electronic storage module
National Institute for Research and Development in Microtechnologies (coordinator) (IMT),
www.imt.roICF is in charge with the piezoelectric layers preparation, deposition and characterisation. IMT designs, develops and optimises the MEMS cantilevers and UPIT deals with the electronic blocks for signal processing and generated energy storage.
The specifications of the piezoelectric microsystem for energy harvesting were defined during 2018. They include: 385 Hz resonant frequency, total area below 1cm2, PZT used as the piezoelectric material and the design of a structure that is using the flexure transversal d31 vibration mode.
Also, two different options of the energy harvesters were designed: one rectangular silicon cantilever (2,500 µm long, 300 µm wide, and 10 µm thick) with a silicon inertial mass and one spiralled rectangular cantilever (equivalent length: 21.6 mm and 300 µm wide). 10 cantilevers were grouped in an array of 2×5 pieces, to increase the power density.
The technological design was performed, by designing the geometries and defining the technological fabrication steps, as well as designing the electronic blocks for energy management and storage.
The deposition methods of the piezoelectric material was defined and developed, including PLD and serigraphic techniques.
Rectangular cantilever with cu inertial mass (simulation)
Spiralled rectangular cantilever (simulation)
The cantilevers connection diagram
Block diagram of the electronic module for the energy management and storage
During 2019, within Project 4, the masks set required for the development of MEMS micro-generator structures was manufactured. The piezoelectric layers were deposited and characterized by the PLD method.
Also, the technological processes for the micro-generators manufacturing were defined and tests were performed for the most important stages, optimizing the process parameters.
At the same time, micro-generator test structures were successfully fabricated, subsequently packaged for characterization and tested. A test circuit for the electronic energy storage module was also developed.
Interface of the vibrations analyses tests, showing the time signal (down) and the FFT deflection spectrum (up)
In the current stage, within Project 4, the masks set required for the fabrication of micro-generator MEMS structures was optimized. Piezoelectric layers of PZT (lead-zirconium-titanate), ZnO-NWs (zinc oxide nanowires) and aluminum nitride (AlN) were deposited and characterized. As the piezoelectric layers of PZT and ZnO-NWs proved difficult to integrate with MEMS technologies, AlN was chosen for the manufacture of energy harvesting structures.
Thus, micro-generator structures were successfully manufactured, which were encapsulated for characterization and testing and the electronic energy storage module was optimized.
Following the testing, MEMS structures were re-optimized to cover a wider range of security applications (aircraft gyro engines) and to increase power flow from the environment.
