Leaky SAW Filter Structure for Low Insertion Loss
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Solution Overview
Problem
Current surface acoustic wave (SAW) devices face challenges in achieving low insertion loss and steep transition bands between pass and stop bands, particularly in communication systems with narrow frequency intervals, due to limitations in manufacturing thin piezoelectric substrates and variations in thickness leading to frequency characteristic issues.
Innovation Solution
A SAW device design featuring a piezoelectric material layer with a thickness of 1 to 2.5 times an acoustic wavelength, paired with busbars and electrode fingers, and reflectors, where the propagation velocity of slow bulk waves in the supporting substrate exceeds that of leaky surface acoustic waves, minimizing propagation loss and spurious generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the piezoelectric substrate thickness is reduced to equal to or less than one acoustic wavelength to reduce insertion loss, then propagation loss is reduced, but manufacturing difficulty increases and frequency characteristic variation becomes large
Solution Approach 1:
The patent changes the thickness parameter of the piezoelectric substrate from the conventional range (equal to or less than one acoustic wavelength) to a specific new range (0.5 to 2.0 times the acoustic wavelength, preferably 0.7 to 1.5 times). This parameter change resolves the contradiction by finding an optimal thickness value that balances propagation loss reduction with manufacturing feasibility and frequency characteristic stability.
2Reliability
If the piezoelectric substrate thickness is reduced to equal to or less than one acoustic wavelength to improve temperature characteristic, then frequency/temperature characteristic is improved, but manufacturing precision requirements become more stringent
Solution Approach 1:
The patent modifies the thickness parameter to a range of 0.5 to 2.0 times the acoustic wavelength (preferably 0.7 to 1.5 times), which relaxes manufacturing precision requirements while maintaining improved frequency/temperature characteristics. This parameter optimization resolves the contradiction between reliability improvement and manufacturing precision demands.
3Ease of manufacture
If the piezoelectric substrate thickness is increased to improve manufacturing ease, then manufacturing difficulty is reduced, but insertion loss increases
Solution Approach 1:
The patent establishes an optimal thickness range (0.5 to 2.0 times acoustic wavelength, preferably 0.7 to 1.5 times) that balances manufacturing ease with insertion loss performance. This parameter optimization resolves the contradiction by identifying a thickness range where manufacturing becomes easier while insertion loss remains acceptably low.
4Manufacturing precision
If the piezoelectric substrate thickness is increased to reduce manufacturing precision requirements, then manufacturing precision requirements are relaxed, but frequency characteristic variation increases
Solution Approach 1:
The patent identifies a specific thickness range (0.5 to 2.0 times acoustic wavelength, preferably 0.7 to 1.5 times) where manufacturing precision requirements are relaxed but frequency characteristic stability is maintained. This parameter optimization resolves the contradiction between manufacturing precision requirements and frequency characteristic stability.
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 design reduces manufacturing difficulties and frequency variations, achieving improved performance by matching minimum propagation loss frequency with spurious frequencies, thus enhancing the SAW device's performance and reducing insertion loss.
Implementation Method 1
a surface acoustic wave device that converts a frequency signal into a surface acoustic wave
Implementation Method 2
A main mode of an elastic wave excited on the piezoelectric material layer by the electrode fingers is a leaky surface acoustic wave
Data Source
AI summary
A surface acoustic wave device includes a piezoelectric material layer, a pair of busbars, a plurality of electrode fingers, and reflectors. The piezoelectric material layer has a thickness that is in a range of 1 to 2.5 times of an acoustic wavelength. A main mode of an elastic wave excited on the piezoelectric material layer by the electrode fingers is a leaky surface acoustic wave. A design variable is set such that a minimum propagation loss frequency where a propagation loss becomes minimum and a frequency of a plate wave spurious formed due to a slow shear wave excited together with the leaky surface acoustic wave are matched. A propagation velocity of a slowest bulk wave of an elastic wave that propagates in a lower layer of the piezoelectric material layer is equal to or more than 1.05 times of a velocity of the leaky surface acoustic wave.