	US 12,395,146 B2
	Composite substrate for acoustic wave device
Yuji Hori, Owariasahi (JP); and Takahiro Yamadera, Nagoya (JP)
Assigned to NGK INSULATORS, LTD., Nagoya (JP)
Filed by NGK INSULATORS, LTD., Nagoya (JP)
Filed on Mar. 4, 2022, as Appl. No. 17/686,804.
Application 17/686,804 is a continuation of application No. PCT/JP2021/023918, filed on Jun. 24, 2021.
Claims priority of application No. 2020-152198 (JP), filed on Sep. 10, 2020.
Prior Publication US 2022/0190804 A1, Jun. 16, 2022
Int. Cl. H03H 9/02 (2006.01); H03H 9/25 (2006.01)

CPC H03H 9/02574 (2013.01) [H03H 9/02559 (2013.01); H03H 9/02866 (2013.01); H03H 9/25 (2013.01)]

3 Claims

1. A composite substrate for an acoustic wave device, said composite substrate comprising:

a piezoelectric material layer;

a supporting substrate; and

x layers (x represents an integer of 3 or larger) of intermediate layers between said piezoelectric material layer and said supporting substrate,

wherein said piezoelectric material layer, said supporting substrate and said intermediate layers satisfy the following formula (1),

wherein the following formula (2) is satisfied when x is an even number, and

wherein the following formula (3) is satisfied when x is an odd number,

R_n<R_n+1 (1)

(In the formula (1),

n represents all of integers of 1 to x,

R_nrepresents an arithmetic average roughness of a surface, on a side of said piezoelectric material layer, of an n′th-order intermediate layer from said piezoelectric material layer, and

R_x+1represents an arithmetic average roughness of a surface, on a side of said piezoelectric material layer, of said supporting substrate,)

V_n−1<V_n (2)

(In the formula (2),

n represents all of even numbers of 2 or larger and x or smaller, and

V_nrepresents an acoustic velocity of said n′th-order intermediate layer from said piezoelectric material layer,)

V_n−1>V_n (3)

(In the formula (3),

n represents all of odd numbers of 1 or larger and x or smaller,

V_nrepresents said acoustic velocity of said n′th-order intermediate layer from said piezoelectric material layer, and

V₀represents an acoustic velocity of said piezoelectric material layer.).