As ceramic materials used for multilayer ceramic capacitors, heretofore, a barium titanate-based compound having a high dielectric constant has been widely known. In addition, as an internal electrode material, a base metal material, such as Ni, which is inexpensive and which has good electrically conductive properties has been widely used.
In this type of multilayer ceramic capacitor, dielectric layers each formed of a dielectric ceramic and internal electrode layers are alternately laminated to each other and are then processed by a firing treatment so as to obtain a ceramic sintered body, and external electrodes are formed on two end portions thereof.
In addition, with the recent advancement of electronic techniques, the reduction in size of a multilayer ceramic capacitor and the increase in capacitance thereof have rapidly progressed.
In addition, with the reduction in size of a multilayer ceramic capacitor and the increase in capacitance thereof, the reduction in thickness of a dielectric ceramic layer also has progressed, and development of a multilayer ceramic capacitor formed of dielectric ceramic layers each having a thickness of 1 μm or less has been aggressively pursued.
Incidentally, when the thickness of the dielectric ceramic layer is reduced, since the electric field to be applied thereto is inevitably increased, it becomes important to ensure the reliability in a high-temperature atmosphere or a high-temperature and high-humidity atmosphere. Since the electric field to be applied is increasingly larger as the thickness of the dielectric ceramic layer is reduced, desired reliability has become difficult to obtain.
Furthermore, in order to obtain a multilayer ceramic capacitor having a large capacitance, an effective area of each of internal electrode layers facing each other is preferably increased. Hence, the reduction in thickness of an external layer portion and the reduction in length from the end portion of the internal electrode layer to the end portion of a ceramic base material have been requested, and a higher humidity resistance has become more difficult to obtain.
In addition, heretofore, it has been aimed to improve the reliability by containing predetermined amounts of various elements in a dielectric ceramic.
For example, Patent Document 1 has proposed a dielectric porcelain composition for a multilayer ceramic capacitor. This dielectric porcelain composition is formed of barium titanate as a primary component and an oxide of Al and contains a plurality of dielectric grains, and those dielectric grains each have an Al concentration which decreases from the surface to the inside of the grain.
According to this Patent Document 1, in order to improve various characteristics, besides the oxide of Al, MgO, V2O5, ZrO2, an MnO2 are not only contained but rare earth oxides containing rare earth elements, such as Y, Dy, Ho, and Gd, are also contained in the dielectric porcelain composition.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-282481 (claims 1 and 6, paragraph Nos. [0035] to [0047], and the like)
USPTO Backgrounds
USPTO Backgrounds