Composite Acoustic Substrate With Concave Velocity Plane
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Solution Overview
Problem
Existing acoustic wave elements using piezoelectric substrates face challenges in minimizing spurious signals between resonance and anti-resonance frequencies due to the convex shape of the inverse velocity plane.
Innovation Solution
A composite substrate is developed, comprising a piezoelectric layer and a low-acoustic-velocity film with a lower acoustic velocity than the piezoelectric layer, which results in a concave inverse velocity plane, reducing spurious signal generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a piezoelectric substrate with a convex inverse velocity plane is used, then the acoustic wave element can be manufactured with conventional structures, but spurious signals are generated between resonance and anti-resonance frequencies
Solution Approach 1:
The invention changes the geometric parameter of the inverse velocity plane from convex to concave by modifying the composite substrate structure. Specifically, it uses a piezoelectric layer combined with a low-acoustic-velocity film (such as silicon oxide) in specific thickness ratios to achieve the concave inverse velocity plane, which eliminates spurious signals while maintaining reliable frequency characteristics
Solution Approach 2:
The invention employs a composite substrate structure consisting of a piezoelectric layer and a low-acoustic-velocity film stacked together. This composite structure enables the formation of a concave inverse velocity plane, where the piezoelectric layer has higher acoustic velocity and the low-acoustic-velocity film has lower acoustic velocity, thereby resolving the spurious signal issue
2Reliability
If a low-acoustic-velocity film is added to create a concave inverse velocity plane, then spurious signals are reduced, but the device structure becomes more complex
Solution Approach 1:
The invention optimizes the thickness parameters of the piezoelectric layer and low-acoustic-velocity film to achieve the concave inverse velocity plane. By controlling the thickness ratio and acoustic velocity relationship between layers, the desired concave shape is obtained without requiring complex additional structures
Solution Approach 2:
The composite substrate uses a simple two-layer structure of piezoelectric material and low-acoustic-velocity film material. This composite approach achieves the concave inverse velocity plane through material selection and layer stacking rather than complex geometric modifications, thereby limiting the increase in device complexity
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
The concave inverse velocity plane effectively reduces the probability of spurious signals between resonance and anti-resonance frequencies, enhancing the frequency characteristics of the acoustic wave element.
Implementation Method 1
the low-acoustic-velocity film 9, on which the piezoelectric layer 11 is stacked, reflects the acoustic waves and contributes to confining the energy of the acoustic waves to the piezoelectric layer 11
Implementation Method 2
a piezoelectric substrate having piezoelectricity at least at a top surface thereof and an IDT (interdigital transducer) electrode located on the top surface of the piezoelectric substrate. Acoustic waves that propagate through the piezoelectric substrate are generated by a voltage being applied to the piezoelectric substrate by the IDT electrode
Data Source
AI summary
A composite substrate includes a piezoelectric layer and a low-acoustic-velocity film. The low-acoustic-velocity film extends along a bottom surface of the piezoelectric layer and has a lower acoustic velocity than the piezoelectric layer. An inverse velocity plane of an acoustic wave propagating through the piezoelectric layer is concave.