CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-248867, filed on 26 Dec. 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a multilayer coil component.

BACKGROUND

Conventionally, a multilayer coil component having a multilayer coil provided in a ferrite element body is known. For example, a multilayer coil component having a ceramic element body in a three-layered structure (a so-called sandwich structure) in which an inner layer portion having relatively high porosity is sandwiched by a pair of outer layer portions having relatively low porosity is disclosed in Japanese Unexamined Patent Publication No. 2005-38904 (Patent Document 1). In such a multilayer coil component, it is known that a dielectric constant and a magnetic permeability increase when the porosity of the element body is low, and a dielectric constant and a magnetic permeability decrease when the porosity of the element body is high.

SUMMARY

After intensive research, the inventors have newly found a technology in which coil characteristics such as impedance, inductance, and self-resonant frequency (SRF) can be adjusted in a multilayer coil component constituted by multi-layered element bodies.

According to the disclosure, a multilayer coil component in which coil characteristics can be adjusted is provided.

A multilayer coil component according to one aspect of the disclosure is a multilayer coil component having a multilayer coil provided in a ferrite element body, and external electrodes respectively provided on end surfaces of the ferrite element body facing each other, in which the ferrite element body includes a first element body portion and a second element body portion adjacent to each other in an axial direction of the multilayer coil, in which a dielectric constant of the second element body portion is lower than a dielectric constant of the first element body portion, and a magnetic permeability of the second element body portion is higher than a magnetic permeability of the first element body portion, and the multilayer coil includes a winding portion and a lead-out portion, the lead-out portion extends from end portions of the winding portion to the end surfaces provided with the external electrodes thereon, in which the winding portion extends over the first element body portion and the second element body portion.

In a configuration in which a winding portion of the multilayer coil is provided only in the inner layer portion and a lead-out portion thereof is provided only in the outer layer portion as in Patent Document 1 described above, it is extremely difficult to adjust coil characteristics. After intensive research, the inventors newly found that a first element body portion and a second element body portion contribute to coil characteristics as follows when a winding portion is provided to extend over the first element body portion and the second element body portion. That is, regarding an impedance around 1 GHz, the first element body portion has a relatively high impedance and the second element body portion has a relatively low impedance. Also, regarding inductance, the first element body portion has a relatively low inductance and the second element body portion has a relatively high inductance. Further, regarding a self-resonant frequency, the first element body portion has a relatively high self-resonant frequency and the second element body portion has a relatively low self-resonant frequency. Therefore, in the above-described multilayer coil component, desired coil characteristics can be obtained by adjusting proportions of the first element body portion and the second element body portion in the ferrite element body.

In a multilayer coil component according to another aspect, an axial direction of the multilayer coil may be parallel to a direction wherein the end surfaces face each other, the end surfaces being provided with the external electrodes.

In a multilayer coil component according to another aspect, the ferrite element body may have a structure in which one of the first element body portions and the second element body portions sandwich the other thereof in the axial direction of the multilayer coil.

In a multilayer coil component according to another aspect, the ferrite element body may include a pair of second element body portions and have a structure in which the first element body portion is sandwiched by the pair of second element body portions in the axial direction of the multilayer coil. In this case, when external electrodes are provided on the second element body portions having a relatively low dielectric constant, high frequency characteristics of the multilayer coil component are improved.

