Structure and Process for High Inductance by Suppressing Magnetic Flux Path between Internal Conductors in Multilayer Ferrite Ceramic Inductor

Abstract

Multilayer ceramic inductors have been developed and miniaturized in order to satisfy the strong demand for the miniaturization of electronic devices. At the same time, high inductance is required even with the small case size. Multilayer ferrite inductors are one of the solutions which meet the demand for high inductance and small case size. Actually, multilayer ferrite inductors are widely used in the market today. However, achieving further high inductance is a problem with such inductors, as, the magnetic flux between the conductors is not interlinked with the other conductors. Therefore, this flux does not contribute to the high inductance. This problem can be solved by locating the non-magnetic material within the magnetic flux path between the area of the inside conductors. However, this is difficult to achieve with the conventional process, which is called the green sheet process. In this process, green sheets of different ceramic materials are formed separately and stacked on each other. Therefore, the different materials are located in discrete layers inside the multilayer device. Previously, we reported on a new processing method for the ceramic green sheet using photo resist film to form the through empty area.[2–4] The photo resist film was exposed optically and developed chemically to form the designed sacrifice patterns. The sacrifice patterns were filled with ceramic slurry using a doctor blade. After the filling process, the sacrifice pattern was dissolved to form the green sheet with the through empty area. The through empty area was filled with the conductive material. This method achieved a flat patterned conductor structure inside the green sheet.