Two-stage lateral bulk acoustic wave filter with capacitive coupling of counter electrode

An acoustic wave filter device comprising:

• a first acoustic wave filter element comprising a first input electrode, a first output electrode, and a first counter electrode,
• wherein the first input electrode and the first output electrode are located on a top surface of a piezoelectric layer, and the first counter electrode is located on a bottom surface of the piezoelectric layer;
• a second acoustic wave filter element comprising a second input electrode, a second output electrode, and a second counter electrode,
• wherein the second input electrode and the second output electrode are located on the top surface of the piezoelectric layer, and the second counter electrode is located on the bottom surface of the piezoelectric layer, the second counter electrode being electrically separated from the first counter electrode;
• and
• a common floating electrode that electrically connects the first output electrode to the second input electrode, so that the first input electrode and the first counter electrode form an input resonator of the acoustic wave filter, and the second output electrode and the second counter electrode form an output resonator of the acoustic wave filter,
• wherein the acoustic wave filter has only one input resonator for applying an input voltage to the device, and one output resonator for obtaining output voltage from the device.