Magnetic performances and switching behavior of Co-rich CoPtP micro-magnets for applications in magnetic MEMS

Abstract

In this paper, the magnetic properties of Co-rich CoPtP films electrodeposited using an optimized Pulse Reverse (PR) technique are investigated for magnetic MEMS applications. By using a combination of forward and reverse pulses with optimized duty cycles during deposition and suitable bath chemistry, the film stress is reduced significantly, which results in smooth, crack-free films of thickness up to 26 μm. The deposited film of thickness ∼3 μm shows a coercivity of 268 kA/m, a remanence of 0.4 T, and a maximum energy product of 35 kJ/m3 in the out-of-plane direction. The variation in the hard-magnetic properties of the films for changing the film thickness is analyzed in terms of the composition, crystalline structure, and grain size. As the thickness is increased from 0.9 μm to 26 μm, the in-plane coercivity reduces by 17% due to an increase of the grain size and the Co content in the alloy structure. The in-plane squareness factor increases by 1.5 times as the thickness is increased over the above-mentioned range, which results in an enhancement of the in-plane remanence value. The magnetization reversal behavior of the deposited films indicates that the nature of magnetic interaction is significantly influenced by the thickness of the films, where the dipolar interaction for the thinner films changes to exchange coupling at higher thickness due to the increase of the grain size. Finally, an innovative design strategy to integrate CoPtP in magnetic MEMS devices by micro-patterning is proposed and analyzed using the finite element method. The demagnetization fields of the magnetic elements are minimized through optimized micro-patterned structures which improve the viability of PR deposited CoPtP micro-magnets having suitable nano-grains in potential MEMS based applications.

Optimization of a vibrating MEMS electromagnetic energy harvester using simulations

“…To further improve the performance of the EM-VEH system, the implementation of more complex permanent magnet architectures such as stripes [8,11], bipolar micro-magnet arrays [15] or two magnetic arrays facing each other with opposite magnetization, as recently proposed by Paul et al [11] is highly promising but requires the specific design of a dedicated coil following the guidelines proposed here.…”

“…The studied parameters to be optimized are the lateral size of the magnets L in a magnet array (100, 300, 500, 900 µm), their interspacing Δx (30, 50, 100, 150 µm) and the coilmagnet distance h (20, 40, 100 µm). Contrary to previous studies [4,8,11], the coil-magnet distance h = 10 µm was not considered here as it is expected to be too difficult to implement in a real device. The number n of columns is adjusted as a function of L and Δx so that the magnetic array fits on the 6×4 mm² plate.…”

“…Up to now, the miniaturization of EM-VEH has suffered from a lack of mature technologies for integrated high performance permanent micromagnets [3,7]. Electrodeposition allows producing thin films and arrays of Co-based materials (CoNiMnP [4], CoPtP [8]) but with limited values of coercivity and remanence, compared to rare-earth based magnets. High-rate triode sputtering combined with topographic or thermomagnetic patterning has been used to fabricate arrays of NdFeB micromagnets with magnetic properties comparable to the best sintered bulk magnets [9].…”

“…The maximum thickness of topographically patterned NdFeB micromagnets has recently been increased to 50 µm [10]. In this framework, several works have recently dealt with the optimization of EM -VEH through magnet design [4,8]. Only a few also take into consideration the complete VEH design, despite the critical role played by the coil design [11,12].…”

“…Considering the inherent technological and size constraints for MEMS, general trends are proposed to maximize the magnetic flux gradient by optimizing the magnet array features (size, interspacing) with respect to the coil design. Interestingly, efficient electromechanical coupling thanks to coil design optimisation can be obtained even for thin film like magnets, which are typically considered inappropriate for use in such devices [4,8].…”