Method for manufacturing piezoelectric bulk acoustic wave element and piezoelectric bulk acoustic wave element
A method for manufacturing a piezoelectric bulk acoustic wave element by forming a sacrificial layer on a part of a primary surface of a substrate. A piezoelectric film sandwiched between a pair of electrodes is formed on the primary surface of the substrate so as to cover the sacrificial layer, the piezoelectric film being formed from scandium-containing aluminum nitride having a scandium atomic concentration with respect to the total number of scandium atoms and aluminum atoms of more than 24 atomic percent. An etching step of removing the sacrificial layer by etching is performed. Prior to the etching step, a protective film formed from aluminum nitride or scandium-containing aluminum nitride having a lower scandium atomic concentration than that of the piezoelectric film is provided so as to cover at least a part of a portion of the piezoelectric film located in a region in which the sacrificial layer is provided.
1. A piezoelectric bulk acoustic wave element comprising:
a substrate;
a piezoelectric film on the substrate and configured so that at least a part of the piezoelectric film is spaced apart from the substrate to form an internal space between the piezoelectric film and the substrate, the piezoelectric film being a scandium-containing aluminum nitride having a scandium atomic concentration with respect to a total number of scandium atoms and aluminum atoms of more than 24 atomic percent, the piezoelectric film having a through hole extending to the internal space;
a pair of electrodes which sandwich the piezoelectric film; and
a protective film covering at least a part of a surface of the portion of the piezoelectric film which is spaced apart from the substrate and at least a part of a surface of the through hole, the protective film being a scandium-containing aluminum nitride having a lower scandium atomic concentration than that of the piezoelectric film.
2. The piezoelectric bulk acoustic wave element according to claim 1 , wherein a diameter of the through hole is smaller proximal to the sacrificial layer.
3. The piezoelectric bulk acoustic wave element according to claim 1 , wherein the scandium atomic concentration of the protective film is 16 atomic percent or less.
4. The piezoelectric bulk acoustic wave element according to claim 1 , wherein the protective film covers the entire surface of the through hole.