Acoustically coupled resonator filter with impedance transformation ratio controlled by resonant frequency difference between two coupled resonators

A coupled resonator filter, comprising:

• a first film bulk acoustic resonator (FBAR), having a first electrical impedance and a first resonance frequency, the first FBAR comprising:
• a first electrode,
• a first piezoelectric layer having a first thickness, disposed on the first electrode, and
• a second electrode disposed on the first piezoelectric layer;
• a second FBAR, having a second electrical impedance and a second resonance frequency, and being disposed over the first FBAR, the second FBAR comprising:
• a third electrode,
• a second piezoelectric layer having a second thickness, disposed on the third electrode, and
• a fourth electrode disposed on the second piezoelectric layer;
• and a
• a coupling layer disposed between the first and the second FBARs,
• wherein the first thickness of the first piezoelectric layer is substantially the same as the second thickness of the second piezoelectric layer,
• wherein the first and second resonance frequencies are substantially different from each other, and
• wherein a thickness of the fourth electrode is substantially different than a thickness of at least one of the first, second, and third electrodes.