Composite Acoustic Substrate With Graded Interlayers for Spurious Suppression
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Solution Overview
Problem
Existing methods for bonding piezoelectric material substrates to supporting substrates result in deteriorated characteristics due to processing-induced denaturation and difficulty in achieving high bonding strength, especially when large roughness is required to suppress spurious bulk waves.
Innovation Solution
A composite substrate is formed with intermediate layers having progressively lower arithmetic average roughnesses from the supporting substrate to the piezoelectric material substrate, and layers with varying acoustic velocities are sequentially arranged to enhance bonding strength and reduce bulk wave reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the back surface of the piezoelectric material substrate is considerably roughened to suppress spurious waves, then the bulk wave reflection is reduced, but the bonding strength between the piezoelectric material substrate and supporting substrate deteriorates
Solution Approach 1:
The bonding interface is segmented into multiple intermediate layers with different roughness values. The roughness is divided into discrete levels (first, second, third intermediate layers) rather than a single uniform rough surface, allowing different regions to serve different functions: some layers provide spurious wave suppression while others maintain bonding strength.
Solution Approach 2:
Different local regions of the bonding interface have different roughness characteristics. The intermediate layers closer to the piezoelectric material substrate have lower roughness to maintain bonding strength, while layers farther away have higher roughness to suppress spurious waves. This local differentiation resolves the contradiction between bonding strength and spurious wave suppression.
2Object-generated harmful factors
If the back surface of the piezoelectric material substrate is roughened to suppress spurious waves, then the bulk wave reflection is reduced, but the characteristics of the piezoelectric material deteriorate due to processing-induced denaturation
Solution Approach 1:
The roughening function is segmented across multiple intermediate layers rather than applying severe roughening directly to the piezoelectric material substrate. This distributes the processing impact and allows the piezoelectric material surface to remain relatively intact, preserving its characteristics while still achieving spurious wave suppression through the intermediate layers.
Solution Approach 2:
Intermediate layers serve as mediators between the piezoelectric material substrate and the supporting substrate. These intermediate layers absorb the roughening function, protecting the piezoelectric material substrate from direct severe processing that would cause denaturation, while still achieving the desired spurious wave suppression effect.
3Device complexity
If a single intermediate layer is used for bonding, then the structure is simple, but it is difficult to simultaneously achieve high bonding strength and effective spurious wave suppression
Solution Approach 1:
The single intermediate layer is segmented into multiple intermediate layers with different roughness values. This segmentation enables the structure to simultaneously achieve high bonding strength (through lower roughness layers) and effective spurious wave suppression (through higher roughness layers), overcoming the limitations of a single-layer design.
Solution Approach 2:
The bonding structure uses a composite of multiple intermediate layers with different roughness characteristics, analogous to composite materials. Each layer contributes different properties (roughness levels) that collectively achieve both bonding strength and spurious wave suppression, which a single homogeneous layer cannot accomplish.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves bonding strength and significantly suppresses spurious waves by reducing bulk wave reflection, maintaining substrate characteristics and ensuring high bonding integrity.
Implementation Method 1
as the intermediate layer having a higher acoustic velocity and intermediate layer having a lower acoustic velocity are provided sequentially adjacent to each other from the piezoelectric material substrate to the supporting substrate, it is found that the reflection of bulk wave can be effectively reduced and the spurious wave is considerably suppressed
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(c)
Figure 3(a)~3(b)
AI summary
(Object) It is to improve the bonding strength of a piezoelectric material substrate and supporting substrate and to effectively reduce the reflection of a bulk wave to suppress the spurious. (Solution) A composite substrate 7A for an acoustic wave device includes a piezoelectric material layer PZ, supporting substrate S and x layers (x represents an integer of 3 or larger) of intermediate layers 1, 2 and X between the piezoelectric material layer and supporting substrate. The piezoelectric material layer, supporting substrate and intermediate layers satisfy the formula (1), and the formula (2) is satisfied in the case that x is an even number and the formula (3) is satisfied in the case that x is an odd number. Rn<Rn+1 (n represents all of integers from 1 to x, Rn represents an arithmetic average roughness of a surface of an n'th-order intermediate layer from the piezoelectric material layer on a side of the piezoelectric material substrate, and Rx + 1 represents an arithmetic average roughness of a surface of the supporting substrate on the side of the piezoelectric material substrate.) Vn−1<Vn (n represents all of even numbers of 2 or larger and x or lower, and Vn represents an acoustic velocity of the n'th-order intermediate layer from the piezoelectric material substrate.) Vn−1>Vn (n represents all of odd numbers of 1 or larger and x or smaller, Vn represents an acoustic velocity of the n'th-order intermediate layer from the piezoelectric material substrate, and V 0 represents an acoustic velocity of the piezoelectric material layer.)