FIG. 11 is a flowchart illustrating an example of a method of manufacturing a resonance apparatus. The resonance apparatus includes an air-gap cavity structure.

Referring to FIG. 11, in operation 1101, a lower electrode is formed to be separated by a predetermined distance from an upper portion of a substrate. For example, the lower electrode may be made of Mo, Ru, W, and/or other conductive materials known to one of ordinary skill in the art. The lower electrode may be used as an input electrode to inject an electrical signal, such as an RF signal, into a piezoelectric layer, and/or as an output electrode to output an electrical signal from the piezoelectric layer. Accordingly, a cavity is formed between the lower electrode and the substrate. Therefore, the lower electrode is separated from the substrate by as much as the cavity. The substrate may be doped with Si. For example, the substrate may include a Si wafer.

In operation 1102, a piezoelectric layer is formed on an upper portion of the lower electrode. For example, the piezoelectric layer may be formed by vapor depositing AlN, ZnO, or lead zirconate titanate on the upper portion of the lower electrode. The piezoelectric layer converts an electrical signal input from the lower electrode or an upper electrode into an acoustic wave.

In more detail, when a temporally changing electric field is induced, the piezoelectric layer converts the electrical signal into a physical oscillation. In addition, the piezoelectric layer converts the physical oscillation into the acoustic wave. The piezoelectric layer 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.