To provide a BAW resonator device in which a resonator satisfies both an electro-mechanical coupling coefficient and a mechanical quality coefficient required for the use of a UWB filter.
The BAW resonator device is provided with a resonator 3 having a lower electrode 31, a piezoelectric layer 32 and an upper electrode 33, on one surface side of a supporting substrate 1, wherein the lower electrode 31 and the upper electrode 33 are formed from an electrode material of which the mechanical quality coefficient is greater than that of a piezoelectric material for the piezoelectric layer 32. As for the resonator 3, a pair of electrode layers are constituted of the lower electrode 31 and the upper electrode 33, and an insulator layer 34 is stacked on an opposite side of the side of the piezoelectric layer 32 in the upper electrode 33. When thickness of the upper electrode 33 is denoted as te, thickness of the insulator layer 34 is denoted as tp and wavelengths of acoustic waves in media of the upper electrode 33 and the insulator layer 34 in a resonant frequency of nth-order mode (n) are denoted as e, p, the thickness te, tp is set so as to satisfy {(n-1)/2}(te/e+tp/p){(n-0.5)/2}.
HAYAZAKI YOSHIKI
MATSUSHIMA CHOMEI
YOSHIHARA TAKAAKI
YAMAUCHI NORIHIRO
Atsuo Mori