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 /spl mu/m thick) with nominally identical geometries of 4 mm/spl times/1.0 mm/spl times/0.13 mm and 30 turns of multilevel copper coils (40 /spl mu/m 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/spl times/4 mm/spl times/0.145 mm and 156 turns of multilevel electroplated copper coils (40 /spl mu/m thick) and electroplated permalloy magnetic core (35 /spl mu/m thick) have slightly higher inductance (about 1.5 /spl mu/H), 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.