Acoustic Wave Filter Thickness Tuning for High-Side Attenuation Poles
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Solution Overview
Problem
Existing communication filter devices face challenges in widening passbands and forming attenuation poles effectively, especially on the high-frequency side, to accommodate increased communication capacity and speed with multiple bands.
Innovation Solution
A filter device incorporating an acoustic wave resonator with a piezoelectric film and interdigital transducer electrode, where the thickness of the piezoelectric film is optimized within specific ranges to utilize sub-resonance for forming attenuation poles, allowing for a wide passband and improved attenuation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a ladder-type surface acoustic wave filter including an inductor is used, then a passband can be widened and an attenuation pole can be formed in a stopband, but the device complexity increases due to the need for additional inductor components
Solution Approach 1:
The patent extracts and eliminates the inductor component from the filter structure. By using a SAW resonator with specifically controlled electrode finger dimensions and spacing, the filter achieves both passband widening and attenuation pole formation without requiring separate inductor components, thus reducing device complexity while maintaining adaptability
Solution Approach 2:
The SAW resonator structure is designed to perform multiple functions simultaneously: it provides both the passband characteristics and the attenuation pole formation that previously required separate components. The interdigital transducer electrodes serve both as the resonating element and as the filtering structure, achieving multi-functionality
2Reliability
If the thickness of the piezoelectric film is increased to improve attenuation characteristics, then attenuation poles can be enhanced, but spurious regions increase
Solution Approach 1:
The patent optimizes the thickness of the piezoelectric film to a specific range (0.05λ to 0.15λ) to achieve the desired balance. By precisely controlling this parameter, the filter achieves effective attenuation characteristics while suppressing spurious region generation, demonstrating parameter optimization to resolve the contradiction
3Adaptability or versatility
If the pitch of electrode fingers is decreased to widen the passband, then frequency response improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies different pitch values to different sections of the electrode fingers. By varying the pitch locally across the electrode structure, the filter achieves passband widening while maintaining manufacturability, as not all regions require the same high precision. This local differentiation resolves the contradiction between performance and manufacturing precision
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 solution enables the creation of a filter device with a steep passband and effective attenuation poles, reducing spurious regions and improving frequency transmission characteristics without the need for additional matching components, thus enhancing communication filter performance.
Implementation Method 1
an acoustic wave resonator including a piezoelectric film having a piezoelectric property
Implementation Method 2
The filter device has a second attenuation pole by using sub-resonance of the acoustic wave resonator
Data Source
AI summary
In a filter device including at least one acoustic wave resonator, the acoustic wave resonator includes a piezoelectric film having a piezoelectric property and an interdigital transducer electrode that is positioned on an upper surface of the piezoelectric film and that includes a plurality of electrode fingers. When a value double a pitch of the plurality of electrode fingers is defined as λ and a duty of the plurality of electrode fingers is defined as d, a thickness T of the piezoelectric film satisfies formula (1) below. The filter device has a second attenuation pole by using sub-resonance of the acoustic wave resonator on a high-frequency side of a passband of the filter device. 0.154λd≤T≤0.264λd(1), where λd satisfies formula (2) below: λd=λ/(−0.6111×d2−0.1792×d+1.2449) (2).