Planarized electrode for improved performance in bulk acoustic resonators

摘要

A bulk acoustic wave, BAW, resonator (200, 225) comprising: a cavity (204) disposed in a substrate (203), a first electrode (205) disposed over the cavity (204) a planarization layer (206) disposed adjacent but not over the first electrode (205), wherein an edge (227) of the planarization layer (206) abuts a termination edge (222, 226) of the first electrode (205), and the cavity (204) has an edge (211) and the planarization layer (206) extends over the edge (211) of the cavity (204) and abuts a terminal edge (210, 226) of the first electrode (205), the first Terminating electrode (205) at a distance (212) from the edge (211) of the cavity (204), the distance (212) being equal to an odd integer multiple of a quarter wavelength, λ / 4, of a complex thickness extension eigenmode which exist outside an active region of the BAW resonator (200, 225) and an upper surface of the first electrode (205) is aligned with an upper surface of the planarization layer (206), and the termination edge (210, 226) is disposed at an angle relative to a surface of the substrate (203) and the planarization layer (206) has a termination edge (227) disposed at a complementary angle to the angle, a piezoelectric layer (207) disposed over the first electrode (205), and a second electrode (201) overlying the piezoelectric layer Layer (207) is arranged.