Acoustic Wave Resonator Layout Using Bulk-Wave Spurious Modes
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Solution Overview
Problem
Existing acoustic wave resonators face challenges in achieving a narrow frequency difference between resonance and anti-resonance frequencies, which affects filter characteristics and efficiency, particularly due to spurious bulk wave emissions.
Innovation Solution
The acoustic wave resonator design incorporates a piezoelectric substrate with a bonded support substrate and IDT electrodes of varying thickness, positioning bulk wave resonance and anti-resonance frequencies between surface acoustic wave frequencies to achieve a narrower frequency difference, utilizing bulk wave spurious emissions for improved resonance characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional SAW resonator design is used, then the structure is simple, but the frequency difference between resonance and anti-resonance is wide resulting in poor filter characteristics
Solution Approach 1:
The patent merges surface acoustic wave (SAW) resonance with bulk acoustic wave (BAW) resonance by positioning BAW resonance frequencies between the SAW resonance and anti-resonance frequencies. This combination creates multiple resonance points that steepen the attenuation slope and improve filter characteristics while maintaining a relatively simple resonator structure consisting of a piezoelectric substrate, IDT electrode, and reflector electrodes.
Solution Approach 2:
The patent changes the physical parameters of the piezoelectric substrate, specifically controlling its thickness to position the bulk wave resonance frequencies at desired locations between the SAW resonance and anti-resonance frequencies. By adjusting substrate thickness and material properties, the BAW resonance can be tuned to achieve optimal filter characteristics with a narrow frequency difference between resonance and anti-resonance.
2Manufacturing precision
If bulk wave spurious emissions are present, then the frequency difference between resonance and anti-resonance becomes wide, but these bulk waves can be utilized to improve resonance characteristics
Solution Approach 1:
The patent converts the harmful bulk wave spurious emissions into beneficial resonance points by positioning the BAW resonance frequencies between the SAW resonance and anti-resonance frequencies. Instead of treating bulk waves as unwanted spurious emissions to be eliminated, the invention utilizes them to create additional resonance points that steepen the attenuation slope and improve overall filter characteristics, effectively turning a harmful factor into a useful feature.
3Ease of manufacture
If the frequency difference between resonance and anti-resonance is wide, then the resonator is easier to design, but the filter efficiency and characteristics deteriorate
Solution Approach 1:
The patent combines SAW and BAW resonance mechanisms to achieve narrow frequency difference between resonance and anti-resonance while maintaining design feasibility. By overlaying BAW resonance points between the SAW resonance and anti-resonance, the design creates a steep attenuation slope that improves filter efficiency without requiring completely new design approaches, thus balancing ease of manufacture with high productivity.
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 enhances the filter characteristics by steepening the attenuation slope at the band edges, improving the acoustic wave filter's performance and efficiency by effectively utilizing bulk wave spurious emissions as resonance points.
Implementation Method 1
a surface acoustic wave resonator (SAW resonator) having a piezoelectric substrate and an IDT (InterDigital Transducer) electrode provided on the top surface of the piezoelectric substrate and exciting a surface acoustic wave (SAW)
Implementation Method 2
A bonded substrate formed by bonding together a piezoelectric substrate and a support substrate having a smaller thermal expansion coefficient compared with the piezoelectric substrate is used for the SAW resonator. By utilizing such a bonded substrate, for example, a change of electrical characteristics of the SAW resonator due to temperature is compensated for.
Implementation Method 3
Between a resonance frequency and anti-resonance frequency due to the surface acoustic wave, one to four of at least one of resonance frequencies or anti-resonance frequencies due to bulk waves are located
Data Source
AI summary
An acoustic wave resonator includes a piezoelectric substrate and an IDT electrode on the top surface of the piezoelectric substrate. Between a resonance frequency and anti-resonance frequency due to a surface acoustic wave, one to four of at least one of resonance frequencies or anti-resonance frequencies due to bulk waves are located.