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To replace NiFe alloys used as flux guides in magnetic microelectromechanical systems, electroplated CoFe thin films were examined. The films were deposited using pulse plating. The results show a strong influence of the reverse current Ireverse on the deposition rate and the saturation flux density Bs. The relative permeability μr is influenced both by the forward current Iforward and by reverse current Ireverse. Based on the examinations an optimized deposition was performed. A film thickness of 15μm was reached during a deposition time of 1h. This film exhibited a saturation flux density Bs of 1.4T, a coercivity Hc of 1130kA∕m, and a relative permeability μr of 290. At this thickness, no delamination occurred and the film showed only minor signs of corrosion, a phenomenon CoFe films are typically prone to.

An important aspect of the development of electromagnetic microactuators is the search for suitable materials as well as the development of the respective deposition and patterning processes. Within the Collaborative Research Center 516 "Design and Fabrication of Active Microsystems", it is the task of the subproject B1 "fabrication of magnetic thin films for electromagnetic microactuators" to perform these investigations. The materials of interest can be divided into two groups: hard magnetic materials and soft magnetic materials. Materials with optimized properties and fabrication processes have been developed within both groups. An example is Samarium-Cobalt (SmCo), which can either be deposited using magnetron sputtering as Sm2Co17 with a very high energy product or in the SmCo5 phase using gas flow sputtering with very high deposition rates. In the area of soft magnetic materials, investigations on Nickel-Iron (NiFe) especially NiFe81/19 were followed by the evaluation of NiFe45/55, which features a higher saturation flux density B (s) and relative permeability mu (r). Furthermore, current investigations focus on Cobalt-Iron (CoFe) and its further increased saturation flux density B (s) and relative permeability mu (r). Current tasks include the stabilization of the fabrication processes to achieve good material properties (i.e. electroplating of CoFe) or a shortening (e.g. by using heated substrates during deposition) by using process alternative not used so far. Another topic is the integration into fabrication processes, i.e. the investigation of process stability and compatibility

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.