Patent ID: 8692440

Claim:
A piezoelectric device having a piezoelectric substrate, a ceiling layer, and an external peripheral wall provided around a key area of said piezoelectric substrate and interposed between said piezoelectric substrate and said ceiling layer, wherein a through-hole is provided in one surface of said piezoelectric substrate so as to reach the other surface of said piezoelectric substrate, a through-hole electrode post connecting said one surface and said other surface through said through-hole is formed, comb-shaped electrodes constituting said key area, and signal input and output terminals connected to opposite ends of said comb-shaped electrodes, are provided on the other surface of said piezoelectric substrate, and an external connection terminal is connected to the one surface of said through-hole electrode post, wherein said ceiling layer comprises a high-density epoxy resin sheet or film as a base material containing glass flakes as a filler therein, where said glass flakes are directed to arrange in the same direction, the size of said glass flakes is set to a range of 6 μm to 150 μm in a long axis direction, 0.1 μm to 0.5 μm in a thickness direction and the mixing ratio of said filler with respect to said base material is set to a range of 40% to 65%.