Acoustic Wave Element Pitch Gradient for Ripple Suppression
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Solution Overview
Problem
Existing acoustic wave elements and filter devices face challenges in preventing ripples on the low-frequency side of their resonant frequency, which affects their performance and isolation characteristics, especially in compact mobile phone front-end circuits.
Innovation Solution
The design incorporates a piezoelectric substrate with interdigital transducer (IDT) electrodes and a reflector, where the IDT-reflector gap and end-side pitches are optimized using specific pitch ratios defined by curves (Formulas 1 and 2) to minimize ripples, ensuring improved isolation and reduced insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inter-center distance between reflector IDT and IDT electrode is reduced to prevent return loss increase, then low-frequency return loss is improved, but ripples may still appear in certain bandwidths
Solution Approach 1:
The patent applies local quality by making the IDT electrode structure non-uniform, specifically reducing the pitch of electrode fingers in the end regions compared to the center region. This local variation in pitch creates different acoustic impedance zones that suppress ripple formation in specific frequency bands while maintaining overall device performance
Solution Approach 2:
The patent changes the pitch parameter of the IDT electrode fingers, creating a gradient structure where the pitch varies from the center toward the ends. This parameter modification allows optimization of the acoustic wave propagation characteristics to eliminate ripples in previously problematic frequency ranges
2Productivity
If multiple filter devices are placed in compact front-end circuits, then data transmission speed is improved through multiband operation, but isolation between adjacent bands and low-loss characteristics become difficult to maintain
Solution Approach 1:
By creating local variations in the IDT electrode pitch, the patent generates frequency-selective characteristics that enhance isolation between adjacent bands. The end-region pitch reduction creates specific transmission windows that improve band separation
Solution Approach 2:
The patent introduces dynamic characteristics to the static IDT structure by creating a pitch gradient that affects different frequency components differently. This allows the device to maintain low-loss characteristics across multiple bands simultaneously
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, enhancing the acoustic wave element's performance by maintaining low insertion loss and improving frequency isolation, making it suitable for compact multi-band mobile phone applications.
Implementation Method 1
an acoustic wave element including a piezoelectric substrate, an interdigital transducer (IDT) electrode on the piezoelectric substrate
Implementation Method 2
an interdigital transducer (IDT) electrode on the piezoelectric substrate and including a pair of comb-shaped electrodes that oppose each other
Implementation Method 3
a reflector located adjacent to the IDT electrode in an acoustic wave propagation direction
Data Source
AI summary
In an acoustic wave element, a distance between a comb electrode finger closest to a reflector and a reflective electrode finger closest to an interdigital transducer (IDT) electrode is set as an IDT-reflector gap. An inter-center distance between adjacent electrode fingers is set as a pitch. The electrode fingers in a direction from the comb electrode finger closest to the reflector toward a center are sequentially set as an n-th end-side electrode finger, and a pitch between the n-th end-side electrode finger and an (n+1)-th end-side electrode finger is set as an n-th end-side pitch. An average value of each pitch by all the comb electrode fingers is set as an average IDT pitch, and an average value of each pitch by the reflective electrode fingers is set as an average reflector pitch.