Integrated electroplated micromachined magnetic devices using low temperature fabrication processes

Micromachining techniques are used to realize inductors and transformers integrated with a multichip package, allowing compact integration with chips, sensors, and other components. The processing steps chosen are all low-temperature, which allows the use of low cost substrates such as MCM-L compatible materials. A variety of micromachined inductors and transformers with different geometries and magnetic core materials are designed, fabricated, tested, and compared. Integrated permalloy and orthonol core inductors (15 μm thick) with nominally identical geometries of 4 mm×1.0 mm×0.13 mm and 30 turns of multilevel copper coils (40 μm thick) show differences in performance due to differences in core behavior. The permalloy core inductor has a slightly higher inductance, but it has much lower dc saturation current than the orthonol core inductor. The effect of insertion of a core air gap was also studied, Although inductors with no air gap having dimensions of 4 mm×4 mm×0.145 mm and 156 turns of multilevel electroplated copper coils (40 μm thick) and electroplated permalloy magnetic core (35 μm thick) have slightly higher inductance (about 1.5 μH), air gap inductors have much higher saturation current (180=250 mA). These devices have high current capability (up to 3 A steady dc current) and are suitable for low power converter applications