Patent ID: 9455647
Filing Date: 2016-09-27
CPC Classification: H02N

Claim Text:
1. An electret element comprising a substrate, an electrically-conductive electrode, and an electret layer comprising a first dielectric layer and a second dielectric layer, wherein: the electret layer is capable of holding electrical charge; the electrically-conductive electrode is on a surface of the substrate; the first dielectric layer is on a surface of the electrically-conductive electrode and has, in a surface opposite to an electrically-conductive electrode-side surface, at least one concave portion having a bottom face, a side wall and a top face; the second dielectric layer covers the entirety of the bottom face and at least a part of the side wall; and a bottom Ec of a conductive band of the second dielectric layer is lower than a bottom Ec of a conductive band of the first dielectric layer, or a top Ev of a valence band of the second dielectric layer is higher than a top Ev of a valence band of the first dielectric layer, wherein a thickness of the first dielectric layer between the bottom face and the surface of the electrically-conductive electrode is thinner than a thickness of the first dielectric layer between the top face and the surface of the electrically-conductive electrode.