Portable magnetic devices
The fabrication and integration of sub-millimeter magnetic materials into predefined circuits is of major importance for POrtable MAgnetic DEvices for the telecommunications, automotive, biomedical and space applications, but remains highly challenging. As reviewed in 2019, the development of sustainable micro energy sources for small and portable devices, such as biomedical implants and wireless sensor networks (IoT devices), is still not achieved despite intensive efforts. The main limitation arises from a lack of mature permanent magnet technology for micro-electro-mechanical systems (MEMS). All these integrated systems share multistep technological processes mastered by semiconducting manufacturers such as implantation, annealing, metallization and reactive etching. To be fully implementable, the permanent magnet (PM) integration should take place without altering the complex architecture of the device.
Downsizing PM made using classical metallurgical processes to yield high performance magnets is incompatible with a monolithic integration on Si-based circuit process flows. Alternative approaches have been intensively sought. The high performance rare-earth materials can be grown by sputtering but are up-to-now limited in thickness, typically to a few tens of microns. On the contrary, electrodeposition and magnetic polymers can yield thick magnets but of reduced strength, due to material limitation or dilution of the magnetic material. There is therefore a need for a compatible process to prepare integrated magnets in the submillimetric range for new developments in microelectronics.
The POMADE project aims at developing new nanostructured magnets (i) at the submillimeter scale, (ii) locally deposited and (iii) integrated into functional devices taking advantage of the most promising approaches developed so far: the dense assembly of aligned cobalt nanorods (NRs) that enable to reach large thickness and magnetic volume fraction, and the high rate sputtering of fully dense NdFeB films that provide high lateral control.
Both approaches will be (i) further developed to reach optimized magnets: submillimeter lateral size control for Co NR assemblies and thicknesses up to 100 µm for NdFeB films, and (ii) adjusted to fulfill the integration criterion: large-scale process (4-inch wafer) and enhanced stability for MEMS process flow compatibility.
Figure 1. Device schematics for a MEMS energy harvester with micromachined magnets
The POMADE project will provide scientific outputs on i) the controlled assembly of hard magnetic nanoparticles using magnetophoresis and capillary forces ii) the optimization of stress release in sputtered thick film. The final objectives being the demonstration of high performance submillimeter magnets integrated in MEMS process flow through a fully compatible approach. These high-performance magnets will be finally integrated into cutting edge device for energy harvesting using MEMS.
The nanostructuration of PMs using MEMS compatible processes raises fabrication, characterization and integration challenges that will be tackled within 3 closely linked work-packages:
- The fabrication of thick submillimeter magnets using Co NRs and NdFeB films
- The advanced structural and magnetic characterization of the PM with high spatial resolution
- The full integration into a MEMS process flow : realization of efficient energy harvesters
POMADE is a multidisciplinary project which combines advanced studies in physical and chemical synthesis, physico-chemical post-synthesis assembly, nanomagnetism and MEMS architecture. The required expertise is gathered within the consortium of Institut Néel, LAAS, IMFT and LPCNO.
Due to the broad interest for high performance integrated magnets and the originality of the POMADE project, success will lead to valorization strategy, as already successfully launched by the recent patent on the fabrication process of Co NR based magnets.
- LPCNO-Toulouse (Lise-Marie Lacroix)
- Institut NEEL - Grenoble (Nora Dempsey)
Lecerf, I., Moritz, P., Angulo-Cervera, J. E., Mathieu, F., Bourrier, D., Nicu, L., ... & Blon, T. (2022). Optimization of a vibrating MEMS electromagnetic energy harvester using simulations. The European Physical Journal Special Topics, 1-7