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.