A sacrificial layer approach to highly laminated magnetic cores

The incorporation of laminations into micromachined magnetic components has the potential to reduce eddy current losses induced in the cores of these components. This paper reports a manufacturing technique for the fabrication of highly laminated cores. The approach is based on an alternating, conformal sequential electroplating of layers of NiFe and Cu, followed by selective sacrificial etching of the Cu. Since the copper sacrificial interlayer is itself conducting, it can act as a plating base for the subsequent deposition of NiFe without the necessity of multiple vacuum steps, multiple coating of insulating layers, or multiple photolithography steps. Highly laminated structures can therefore be achieved merely by alternating plating baths during fabrication, followed by selective removal of the Cu layers to provide electrical insulation between the magnetic layers. The fabrication approach can be readily adapted to a wide range of core geometries. To illustrate the improvements in magnetic properties achievable using this technique, the magnetic core fabrication technology has been successfully combined with integrated solenoid-like coils in order to fabricate a complete integrated inductor, which has been designed to operate in the low MHz range for power conversion applications. Inductors with highly laminated cores fabricated using the sacrificial layer approach exhibit quality factors exceeding those of unlaminated core devices by a factor of 2-3 at a frequency of 1 MHz.