BAW resonator having piezoelectric layers oriented in opposed directions

A bulk acoustic wave filter comprising at least one bulk acoustic wave resonator, the at least one bulk acoustic wave resonator comprising

• a first piezoelectric layer made of a material oriented toward a first direction;
• and a second piezoelectric layer made of a material oriented toward a second direction opposed to the first direction;
• the first piezoelectric layer and the second piezoelectric layer being acoustically coupled with each other;
• a first electrode, on which the first piezoelectric layer is at least partially formed;
• a second electrode formed at least partially on the first piezoelectric layer, the second piezoelectric layer being at least partially arranged on a first portion of the second electrode;
• an additional first piezoelectric layer arranged at least partially on a second portion of the second electrode, the second piezoelectric layer and the additional first piezoelectric layer being arranged so as to be spaced apart from each other;
• a third electrode arranged at least partially on the second piezoelectric layer;
• and
• a fourth electrode arranged at least partially on the additional first piezoelectric layer.

A method of manufacturing a bulk acoustic wave resonator comprising the steps of:

• forming a first piezoelectric layer having a first polarization;
• forming a second piezoelectric layer having a second polarization at a distance above the first piezoelectric layer, the second polarization opposite the first polarization;
• and
• forming above the first piezoelectric layer a third piezoelectric layer having the first polarization, the third piezoelectric layer at the same distance above the first piezoelectric layer as the second piezoelectric layer and spaced apart from the second piezoelectric layer.