Method for manufacturing piezoelectric thin-film element

A method of manufacturing a piezoelectric thin-film element, comprising:

• a first step of forming, on one surface of a piezoelectric single-crystal substrate made of a single crystal of a piezoelectric material, a first electrode in a predetermined planar shape with an area smaller than that of the piezoelectric single-crystal substrate;
• a second step of forming a second electrode that has an area different from that of the first electrode on one surface of a multilayered acoustic film consisting of a plurality of layers different in acoustic impedance which are alternately piled;
• a third step of affixing the first electrode and the second electrode to each other;
• a fourth step of thinning the piezoelectric single-crystal substrate, such that the second electrode, the first electrode, and a piezoelectric thin film obtained by thinning the piezoelectric single-crystal substrate are piled on the multilayered acoustic film, wherein the piezoelectric thin film is obtained by thinning the piezoelectric single-crystal substrate from the other surface of the piezoelectric single-crystal substrate by polishing, and an electrode formation region where the first electrode is formed is preferably made thinner than a non-electrode formation region around the electrode formation region, where the first electrode is not formed, by a polishing pressure difference between the electrode formation region and the non-electrode formation region;
• and
• a fifth step of forming, on the piezoelectric thin film, a third electrode that faces the first electrode with the piezoelectric thin film in between and has an area larger than that of the first electrode.