Directional Permeability Dependence in Electroplated Permalloy Layers

Abstract

Flux guides made of soft magnetic thin-film material are an important component of micro actuators based on electromagnetic transducer principles. One essential property of soft magnetic films is the relative permeability µr. To achieve a low magnetic resistance (reluctance), a high relative permeability µr is required. While the permeability in patterned flux guides located in the wafer plane typically can be determined rather easily (it typically is similar to the permeability of non-patterned films) the permeability in patterns with a flux perpendicular to the wafer plane quite often is unknown. However, for the magnetic behavior of the whole thin-film core it is of utmost importance. Flux guides often feature a thickness of some ten micrometers, but lateral dimensions of hundreds of micrometers or even some millimeters and therefore are subject to demagnetization effects. Therefore, any permeability measurement on patterned magnetic films has to take the influence of the flux guide geometry into account. This paper describes an approach to determine the real average relative permeability µr along the main axes, i.e. parallel and perpendicular to the wafer surface, by using special multiple probes, subjecting the probes to a Vibrating Sample Magnetometer (VSM) test to determine the apparent relative permeability µr,app of a probe, and calculating the real relative permeability µr,real by taking the demagnetization factor into account.