A planar micromachined spiral inductor for integrated magnetic microactuator applications

In this work, planar micromachined spiral inductive structures with relatively high inductance at low (Hz-kHz) frequencies are designed and fabricated for integrated magnetic microactuator applications and other purposes. Two types of multilayer micromachined inductors have been investigated. The first structure is a standard planar inductor spiral. To this structure we have added an electroplated high-permeability nickel-iron (Ni/Fe) magnetic core, which forms a central core to concentrate flux and completely encapsulates the windings, thus minimizing magnetic interference. For a typical 36-turn device 3 mm*3 mm in area, an inductance of approximately 20 mu H was obtained. The structure with a magnetic core has an inductance four to five times greater than a similar structure without a magnetic core. The specific inductance of our structure (inductance per unit area) is 2.2 mu H mm -2 at 10 kHz, which is one of the highest inductance values ever achieved in an integrated planar inductive component at low frequency. Since the structure of the spiral-type inductor is similar to those of planar magnetic microactuators such as micropumps, microvalves and microrelays, several low-frequency microactuator applications are expected to be possible with this inductor.