Saturation Flux Density Bs Research Articles

Influence of Deposition Parameters on Mechanical Stress and Magnetic Properties in Thick, Electroplated Co-Fe Flux Guides

A notable advantage of electroplated binary Co-Fe alloys in MEMS applications like sensors and actuators is the high saturation flux density BS, which may reach values of 2.4 T in a composition range of 50 – 70 wt% Fe. In contrast, there are certain disadvantages limiting the use of these alloys, e. g. high film stress, high corrosion sensitivity and high magnetostriction. The mechanical and magnetic properties of Co-Fe films influence each other strongly. They are determined by the films’ microstructure, given by film texture, grain size and morphology, structural defects and impurities. In this study, the effect of process conditions like current density, pulse duration, duty cycle, pH-value of the plating bath and application of a constant magnetic field parallel to the electrode surface on film stress, microstructure and magnetic properties are examined.

Investigation on a NiFe alloy with a coefficient of thermal expansion matching the one of silicon

Thin-film materials with a high relative permeability μr play an important role in the design of magnetic microactuators. Since the relative permeability μr is affected by external parameters such as film thickness and internal stress, investigations were carried out to determine the influence of film stress caused by different coefficients of thermal expansion of substrate and magnetic film, especially in combination with an annealing process at high temperatures. When using a soft magnetic material with a coefficient of thermal expansion close to the one of the substrate, the stress can be minimized. A suitable combination is NiFe35∕65 and Si substrates. Investigations on the thermal match of the two materials, as well as the relative permeability μr, the coercivity Hc, and the saturation flux density BS, were carried out as functions of the deposition temperature tdep. The relative permeability increases from 200 to greater than 1000 at temperatures above 400°C, while the coercivity Hc decreases from 2000to1000A∕m.