Patent ID: 8624690

Claim:
A surface acoustic wave device comprising: a sapphire substrate having a C-plane main surface; an aluminum nitride film which is formed on the main surface of the sapphire substrate; comb-like electrodes which are formed on the surface of the aluminum nitride film to excite surface acoustic waves; and a silicon dioxide film which covers the comb-like electrodes and a surface of the aluminum nitride film, wherein the surface acoustic waves which are excited by the comb-like electrodes are first-order Sezawa waves; when a thickness of the aluminum nitride film is ta, a thickness of the silicon dioxide film is ts, and a wavelength of the surface acoustic waves is λ, a relationship between a normalized film thickness of the aluminum nitride film is expressed by KH—AlN=(2λ/λ)·ta and a normalized film thickness of the silicon dioxide film is expressed by KH—SiO 2 =(2π/λ)·ts; and when the normalized film thicknesses are represented by the following coordinates: coordinate 1 (KH—SiO 2 ,KH—AlN)=(2.00,0.88) coordinate 2 (KH—SiO 2 KH—AlN)=(2.50,1.13) coordinate 3 (KH—SiO 2 ,KH—AlN)=(2.76,1.42) coordinate 4 (KH—SiO 2 ,KH—AlN)=(2.77,1.75) coordinate 5 (KH—SiO 2 ,KH—AlN)=(2.60,3.00) coordinate 6 (KH—SiO 2 ,KH—AlN)=(2.57,4.00) coordinate 7 (KH—SiO 2 ,KH—AlN)=(2.60,5.00) coordinate 8 (KH—SiO 2 ,KH—AlN)=(2.74,5.96) coordinate 9 (KH—SiO 2 ,KH—AlN)=(2.80,6.83) coordinate 10 (KH—SiO 2 ,KH—AlN)=(2.80,7.83) coordinate 11 (KH—SiO 2 ,KH—AlN)=(2.82,8.67) coordinate 12 (KH—SiO 2 ,KH—AlN)=(2.82,10.00) coordinate 13 (KH—SiO 2 ,KH—AlN)=(2.00,10.00), KH—AlN and KH—SiO 2 are within an area defined by connecting the coordinates in order of the coordinate 1 to the coordinate 13 and connecting the coordinate 13 and the coordinate 1.