ALD Agglomerated Permanent Micromagnets for MEMS Applications

PowderMEMS® introduces a novel technique leveraging atomic layer deposition (ALD) to agglomerate powder materials into rigid, organic-free permanent micromagnets for micro-electro-mechanical systems (MEMS). A low-temperature ALD process (75 °C) using aluminum oxide was developed to address MEMS fabrication constraints. Despite being below ALD's temperature window, agglomeration was achieved and compared to results at 300 °C, revealing increased agglomeration depth with higher temperatures. Optimizing diffusion time and particle size enhanced agglomeration efficiency, reducing processing time for four wafers from 60 to 29 hours per cycle.

Fabricated NdFeB micromagnets on 8-inch Si wafers exhibited coercivity of 911 mT and remanence of 430 mT. Structural analysis using TEM revealed nanocrystalline grains with tetragonal phases and conformal ALD coatings. Magnetic characterizations, complemented by Wohlfarth and Henkel plots, identified dominant long-range magnetostatic interactions. High-temperature ALD processing caused oxidation at particle surfaces, while larger particle sizes (d50 = 25 µm) improved thermal stability.

Collaborating with Fraunhofer IFAM, automated tools increased packing density and streamlined wafer processing, advancing the technology’s manufacturing readiness level. Corrosion stability tests using PECVD-deposited silicon oxide layers revealed improved resistance but highlighted pinhole-related failures.

Integrating micromagnets into cantilever beam structures for MEMS piezoelectric energy harvesters demonstrated open-circuit voltages of 6 V and power outputs exceeding 100 µW in resonance, with successful frequency up-conversion yielding 74 µW RMS power at low frequencies. These advancements position PowderMEMS® as a transformative technology for sustainable energy harvesting in industrial, wearable, and remote sensing applications.

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