S0 Plate Wave Resonator Reflective Layer for Spurious Response Suppression
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Solution Overview
Problem
Elastic wave devices using plate waves often experience spurious responses near resonant or anti-resonant frequencies and pass bands, leading to increased loss due to decreased reflectivity of the acoustic reflective layer.
Innovation Solution
The elastic wave device incorporates a support substrate with an acoustic reflective layer comprising alternating low and high acoustic impedance layers, where the thickness ratio of these layers is optimized between 0.35 and 0.65, and a piezoelectric body made of lithium niobate to minimize spurious responses and enhance electromechanical coupling, thereby reducing loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the acoustic reflective layer uses conventional thickness ratios, then the structure is simple, but spurious responses appear near resonant frequency or anti-resonant frequency
Solution Approach 1:
The patent applies parameter changes by optimizing the thickness ratios of the acoustic reflective layer. Specifically, the first thickness t1 is set to 0.15-0.35 times the wavelength λ, and the second thickness t2 is set to 0.10-0.25 times the wavelength λ, with their sum t1+t2 being 0.25-0.60 times the wavelength λ. These specific parameter ranges suppress spurious responses near resonant and anti-resonant frequencies while maintaining practical device complexity.
Solution Approach 2:
The acoustic reflective layer is constructed as a composite structure with multiple layers having different acoustic impedances. The patent specifies alternating low-acoustic-impedance layers (with impedance Z1) and high-acoustic-impedance layers (with impedance Z2), where Z1/Z2 is between 0.3-0.7. This composite material approach enables effective suppression of spurious responses through impedance mismatch and wave interference.
2Loss of energy
If the acoustic reflective layer thickness is not optimized, then manufacturing is easier, but reflectivity decreases causing increased loss
Solution Approach 1:
The patent defines specific parameter ranges for the acoustic reflective layer thicknesses to optimize reflectivity and minimize energy loss. The first thickness t1 is set to 0.15-0.35λ, the second thickness t2 is set to 0.10-0.25λ, and their sum t1+t2 is set to 0.25-0.60λ. These parameter specifications ensure high reflectivity while providing clear manufacturing targets that balance precision requirements with manufacturability.
Solution Approach 2:
The patent replaces simple geometric thickness control with a more sophisticated approach based on acoustic impedance matching and wave interference principles. By designing the layer structure with specific impedance ratios (Z1/Z2 = 0.3-0.7) and thickness ratios, the system achieves high reflectivity through acoustic field manipulation rather than relying solely on mechanical dimensioning, thereby reducing sensitivity to manufacturing tolerances.
3Reliability
If conventional acoustic reflective layer designs are used, then device structure is simpler, but spurious responses appear near pass band in filter applications
Solution Approach 1:
For filter applications, the patent specifies optimized parameter ranges: the first thickness t1 is set to 0.20-0.35 times the wavelength λ, and the second thickness t2 is set to 0.15-0.30 times the wavelength λ, with their sum t1+t2 being 0.35-0.60 times the wavelength λ. These parameter changes effectively suppress spurious responses near the pass band while maintaining reasonable structural complexity.
Solution Approach 2:
The patent applies local quality by differentiating the acoustic reflective layer design between resonator and filter applications. For filters, the thickness parameters are specifically optimized (t1 = 0.20-0.35λ, t2 = 0.15-0.30λ) to address the specific requirement of suppressing spurious responses near the pass band, rather than using a universal design for all applications.
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 configuration effectively suppresses spurious responses near resonant frequencies in resonators and pass bands in filters, achieving low-loss operation by optimizing the reflectivity and electromechanical coupling of the S0 mode plate waves.
Implementation Method 1
a piezoelectric body that is laminated directly or indirectly on the acoustic reflective layer
Implementation Method 2
The acoustic reflective layer causes plate waves propagating in the piezoelectric body to be confined at least in the piezoelectric body
Data Source
AI summary
An elastic wave device using the S0 mode of plate waves includes a support substrate, an acoustic reflective layer laminated on the support substrate, a piezoelectric body laminated on the acoustic reflective layer, and an IDT electrode disposed on the piezoelectric body. In the acoustic reflective layer, T1+T2 is between about 0.40 and about 0.60 inclusive in a portion in which low and high acoustic impedance layers are adjacent in the laminating direction. T1 is the thickness of the low acoustic impedance layers. T2 is the thickness of the high acoustic impedance layers. T1/(T1+T2) is between about 0.35 and about 0.65 inclusive.