Innovative integrated microsystems for hybrid power generation

Project leaders

Mariaassunta Signore, Vladimir Kolesov

Agreement

RUSSIA - RFBR-suspended - Russian Foundation for Basic Research

Call

CNR/RFBR triennio 2018-2020 2018-2020

Department

Chemical sciences and materials technology

Thematic area

Chemical sciences and materials technology

Status of the project

New

Research proposal

In the recent decades, energy consumption within the world has had a prosperous trend. Therefore, many efforts have been made to find new solutions for energy crisis by turning the eyes into renewable energy sources not only produced from sun, wind and water but also from not conventional sources as mechanical vibrations, temperature gradient, bio electricity, useful for low power consumption. As an upshot of these efforts, latterly proposed alternative energy sources are microbial fuel cell (MFC) and miniaturized energy harvesters. MFC uses an active microorganism as a biocatalyst in an anaerobic anode compartment for production of bioelectricity while energy harvesters convert the mechanical energy, coming from vibrations, into electrical one. An innovative solution could be represented by the design and fabrication of a hybrid microsystem which harvests energy from different green sources. The focus of this research proposal is to develop the technological solutions and design methodologies to integrate, in only one system, different devices which harvest energy from not conventional sources, such as piezoelectric vibration harvesters, developed by CNR, and MFC, developed by IRE. Piezoelectric harvesting technology answers to the requirement to provide a valid alternative to conventional batteries for wireless sensors, especially when the batteries changing is unpractical. Among different types of harvesters (photovoltaic, electrostatic, thermo-electric, vibrational), vibrational ones, based on the conversion of the mechanical energy, coming from vibrations, into electrical power in the mW/mW range, are widely preferred because of the simplicity of design and fabrication. This conversion can be obtained through three main methods: electromagnetic, electrostatic and piezoelectric. This last one appears to be the winning technology because piezoelectric harvesters supply the highest reported energy density per volume and show a higher flexibility of being integrated into a system. Moreover, they cover the fundamental requirements of reasonable power production with wide bandwidth, small volume, low weight and low-cost. Piezoelectric harvesters utilize the ability of smart materials, like piezoelectric ones, to generate electrical power in response to the external mechanical deformation by using relatively low frequency and low acceleration vibrational sources. MEMS-scale devices are favorable in portable systems to reduce their overall size, and they can be the only choice in some applications requiring one-time installation and no regular maintenance (i.e. in vivo biosensors). Technological efforts are aimed to improve the harvested power of MEMS micro-generators by optimizing the device geometry design, the coupling mode operation and the quality of the piezoelectric active material. In particular, the choice of the piezoelectric material is crucial for the MEMS harvester. Among the broad range of piezoelectric materials, PZT, ZnO and AlN are the most studied. AlN-based MEMS piezoelectric harvesters have been on high demand because of their CMOS compatible fabrication process. Moreover, AlN has proven to be the superior piezoelectric ceramic for harvesting applications owing to its high energy density, moderate voltage levels, low dielectric constant and especially for the easiness to deposit nitride thin films of good quality at low temperature. AlN or transition metals AlN-doped are proposed as active thin films. they could be deposited by radio frequency (RF) magnetron sputtering, a preferred growth technique due to its low cost, low operating temperature, good process reproducibility and compatibility with micromachining technologies. Thin films will be characterized form morphological and structural point of view, in order to monitor the crystallinity and the formation of (002)-orientation of their hexagonal structure which ensures the enhancement of the harvester response. The piezoelectric characterization will be performed too before the integration of the thin films into the final device. The comparative study of different piezoelectric materials is aimed to maximize the output power of the harvester. Suitable metallic materials for the electrodes will be selected, taking into account that the device response on mechanical excitation is not a mere characteristic of the only piezoelectric thin film but it depends strongly also on the underlying structure (substrate and electrode layers). An unimorph rectangular cantilever beam geometry is initially proposed, operating in 31-mode which is more widely used compared to the 33-mode because of its lower coupling coefficient that guarantees the minimization of energy loss. Then, more complex geometries (i.e. triangular or trapezoidal cantilever, array of beams) could be exploited, together with nonlinear approaches for bandwidth enhancements (i.e bistable oscillation mode with magnetic sources integration). Key aspects, including beam geometry, piezoelectric active area, thicknesses of the structural layers and specifically designed electronic circuits, will be investigated for the realization of a piezoelectric harvester with unprecedented characteristics in terms of output power. All these parameters will be taken into account in a finite element modeling (FEM)-based optimization method to model the piezoelectric energy harvesters. Different cantilever structures will be created in a commercial FEM tool - COMSOL Multiphysics - and various simulations will be carried out to observe the effects of different investigated parameters on the harvester output power. The best parameters will be defined for the fabrication of the final device which will be properly characterized to validate both the whole fabrication process and its suitability to power portable electronics. Magneto-elastic potential distribution will be calculated by FEM tools for nonlinear devices.

Research goals

The overall objective of the project "Innovative integrated microsystems for hybrid power generation", for the Italian counterpart, consisted into developing suitable technologies to produce power from clean energy sources. MEMS is a winning technology, mainly for the fabrication of piezoelectric energy harvester aimed to advance the research frontier towards more integrated and more autonomous MEMS devices. The integration of piezoelectric materials, which naturally convert the commonly unused mechanical energy, coming from environment vibrations, into electrical energy, represented an extraordinary success in this field. In particular, the specific objective of the proposal is to design, model, fabricate and test a miniaturized piezo-MEMS energy harvester on a standard silicon substrate, with unprecedented characteristics in terms of output power. The advantages of this approach would be the increased harvester efficiency and further integration of the silicon technology with the characteristic potentialities of smart materials like piezoelectric ones. A piezoelectric harvester demonstrator, with the optimized parameters, will be produced to prove the feasibility of the various technologies and operation modes and the integration between them. The proposed research will supply a well-defined process for the fabrication of highly efficient and low cost piezoelectric micro-generators exhibiting performance such to power the next generation of autonomous devices.

Last update: 03/08/2025