A MAGNETIC THIN-FILM INDUCTOR AND ITS APPLICATION TO A MHZ SWITCHING DC-DC CONVERTER

The authors propose a novel structured magnetic thin film inductor usi ng rotation magnetization only. The thin film inductor has a sandwich structure, which consists of a double-rectangular spiral coil between top and bottom CoZrNb amorphous thin films. The sputtered CoZrNb amorp hous magnetic thin films have uniaxial magnetic anisotropy induced by direct current field annealing. The easy magnetization axis is directe d to the main axis of the rectangular spiral coil. Hence, only the rot ation magnetization process dominates in this device. The typical spec ifications are as follows; 3.5 x 5.5 mm in size, inductance of 1 muH c onstant up to 10 MHz, and a quality factor of 10 at 10 MHz. A MHz swit ching chopper dc-dc converter has been developed by using this thin fi lm inductor, bare-chip semiconductor devices (a power MOSFET and a Sch ottky barrier diode), and a multilayer ceramic capacitor. This convert er with a 0.1 cc volume has an output power over 1 W at 5 MHz switchin g, and the power density exceeds 10 W/cc (160 W/in3.).