Acoustic Wave Element Pitch Variation for Ripple Suppression
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Solution Overview
Problem
Existing acoustic wave filter devices face challenges in preventing ripples on the low-frequency side of their resonant frequency, which affects their performance and efficiency, especially in compact mobile phone front-end circuits where high isolation and low-loss characteristics are required.
Innovation Solution
The acoustic wave element design includes a piezoelectric substrate with comb-shaped IDT electrodes and a reflector, where the average pitch of the comb electrodes is smaller than that of the reflective electrodes, and specific pitch configurations are implemented to reduce or prevent ripples by adjusting the positions of the comb electrode fingers relative to the reflector, ensuring that at least one n-th end-side pitch is smaller than the average pitch and at least one m-th inner-side pitch is larger than the average pitch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inter-center distance between the IDT electrode and reflector is reduced to 0.45 times or less of the reflector wavelength, then return loss on the low-frequency side is improved, but ripples may still appear in some bandwidths
Solution Approach 1:
The patent applies local quality by varying the pitch of comb electrode fingers in different regions. Specifically, the pitch is set to be smaller than the average pitch in the region closer to the reflector (n-th end-side pitch where 1≤n≤0.233×N), and larger than the average pitch in the region closer to the center (m-th inner-side pitch where 1≤m≤0.167×N). This localized pitch variation suppresses ripples in specific frequency bands while maintaining overall device performance.
Solution Approach 2:
The patent changes the pitch parameter of comb electrode fingers to suppress ripples. By setting specific pitches (n-th end-side pitch and m-th inner-side pitch) different from the average pitch, the resonant frequencies of the comb electrodes are adjusted to avoid overlapping with the passband, thereby suppressing ripples without requiring further reduction of the IDT-reflector distance.
2Volume of moving object
If multiple filter devices are disposed in a compact front-end circuit, then mounting space is reduced, but achieving high isolation and low-loss characteristics becomes more difficult
Solution Approach 1:
The patent changes the pitch parameter of comb electrode fingers to suppress ripples and improve frequency characteristics. By optimizing the pitch distribution, the device achieves better isolation between adjacent bands and reduced insertion loss in the passband, allowing compact arrangement of multiple filter devices without compromising performance.
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 reduces or prevents ripples on the low-frequency side of the resonant frequency, enhancing the acoustic wave element's performance by minimizing insertion loss and improving frequency characteristics.
Implementation Method 1
an acoustic wave element includes a piezoelectric substrate, an IDT electrode on the piezoelectric substrate
Implementation Method 2
a reflector adjacent to the IDT electrode in an acoustic wave propagation direction
Data Source
AI summary
An acoustic wave element includes a piezoelectric substrate, an IDT electrode including comb electrode fingers, and a reflector including reflective electrode fingers. An average value of all pitches of the comb electrode fingers is smaller than an average value of all pitches of the reflective electrode fingers. When a total number of the comb electrode fingers is defined as N, at least one n-th end-side pitch satisfying 1≤n≤(0.233×N) is smaller than the average value of all the pitches of the comb electrode fingers.