The piezoelectric layer 104 is formed on an upper portion of the lower electrode 102, and on the upper portion of the substrate 101. For example, the piezoelectric layer 104 may be formed by vapor depositing an aluminum nitride (AlN), a zinc oxide (ZnO), or a lead zirconate titanate, on the upper portion of the lower electrode 102, and on the upper portion of the substrate 101. The piezoelectric layer 104 converts an electrical signal input from the lower electrode 102 or the upper electrode 105 into an acoustic wave.

In more detail, when a temporally changing electric field is induced, the piezoelectric layer 104 converts the electrical signal into a physical oscillation. The piezoelectric layer 104 converts the physical oscillation into the acoustic wave. The piezoelectric layer 104 generates the acoustic wave to be a bulk acoustic wave based on the induced electric field in a same direction as an oscillation direction in an oriented piezoelectric film.

As shown in FIG. 1, the conductive layers 106 and 107 are formed on a lower portion of the lower electrode 102 and an upper portion of the upper electrode 105, respectively. For example, the conductive layers 106 and 107 may be formed by vapor depositing a conductive material on the lower portion of the lower electrode 102 and the upper portion of the upper electrode 105, respectively. The conductive material may include, for example, silver (Ag), copper (Cu), gold (Au), Al, calcium (Ca), W, zinc (Zn), nickel (Ni), iron (Fe), platinum (Pt), carbon steel, lead, grain-oriented electrical steel, manganin, constantan, stainless steel, and/or graphite.