Method for manufacturing piezoelectric thin film resonator

A method for manufacturing a piezoelectric thin film resonator, comprising:

• forming a buffer layer including MgO or SrO, above a single-crystal sapphire substrate;
• forming a piezoelectric thin film above the buffer layer;
• forming a first electrode above the piezoelectric thin film;
• forming a protection layer above the first electrode;
• preparing a silicon substrate having a silicon oxide layer;
• bonding the silicon substrate to the single-crystal sapphire substrate having the buffer layer, the piezoelectric thin film, the first electrode and the protection layer;
• separating the single-crystal sapphire substrate from the piezoelectric thin film by etching the buffer layer;
• after separating the single-crystal sapphire substrate from the piezoelectric thin film forming a second electrode above the piezoelectric thin film;
• and
• patterning the second electrode, the piezoelectric thin film and the first electrode.