Permanent magnet microstructures using dry-pressed magnetic powders

Abstract

This paper presents microfabrication methods and performance analysis of bonded powder permanent magnets targeting dimensions ranging from 10 µm to greater than 1 mm. For the structural definition and pattern transfer, a doctor blade technique is used to dry press magnetic powders into pre-etched cavities in a silicon substrate. The powders are secured in the cavities by one of the three methods: capping with a polyimide layer, thermal reflow of intermixed wax-binder particles, or conformal coating with a vapor-deposited parylene-C film. A systematic study of micromagnets fabricated using these methods is conducted using three different types of magnetic powders: 50 µm Nd–Fe–B, 5 µm Nd–Fe–B and 1 µm barium ferrite powder. The isotropic magnets are shown to exhibit intrinsic coercivities (Hci) as high as 720 kA m–1, remanences (Br) up to 0.5 T and maximum energy products (BHmax) up to 30 kJ m–3, depending on the magnetic powder used. Process compatibility experiments demonstrate the potential for the magnets to withstand typical microfabrication chemical exposure and thermal cycles, thereby facilitating their integration into more complex process flows. The remanences are also characterized at elevated temperatures to determine thermal sensitivities and maximum operating temperature ranges.

Integration of Thick-Film Permanent Magnets for MEMS Applications

“…Embedding magnetic particles into silicon structures has been previously demonstrated using various binding methods including polyimide thin film, wax composite, and Parylene C [20]. Figure 1 shows a schematic of a method of integrating magnetic powders by embedding the powders into an etched cavity of silicon.…”

“…The most common method involves mixing the magnetic powder into a polymer matrix in order to bind the powder into a film. The polymer can then be cast using molding, spinning, or screen printing techniques [20]. Various types of polymer matrixes have been developed including: polyimide [21], [22], SU-8 [23], PMMA [24], PDMS [25] and wax [26].…”

“…Homogeneity of the magnetic powder/polymer mixtures is also a major concern for reproducibility, as the powders are not uniformly distributed in the film. Recently Parylene C, which is a CVD (Chemical Vapor Deposition) deposited polymer has been used as a binding material to improve the fill fraction [20], [30]. Previously the magnetic powders were deposited into silicon etched cavities using a doctor blade technique.…”

Performance Characterization of Micromachined Inductive Suspensions Based on 3D Wire-Bonded Microcoils

“…The red square points are experimental measurement. The black line is the theoretical curve generated by Equation (6) assuming that δ = 20 µm and α = 0.8. Figure 7.…”

“…Inductive levitation in conjunction with microfabrication techniques has the advantage of operating without permanent micromagnets, which are otherwise difficult to implement and, in spite of notable recent efforts in the field [4][5][6], are still rather incompatible with MEMS technology.…”