Piezoelectric Substrate Layout to Prevent Elastic Wave Insertion Loss
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Solution Overview
Problem
Elastic wave devices experience increased insertion loss due to polarization reversal in piezoelectric substrates, which is exacerbated by electric charge generation from the piezoelectric and pyroelectric effects.
Innovation Solution
The design includes a piezoelectric substrate with an inclined polarization axis, interdigital transducer electrodes, and electrode lands that facilitate the transfer of electric charge away from the substrate's side portions, reducing the likelihood of polarization reversal by connecting electrode lands to the busbars and signal potential, and using connecting lines and bumps for efficient charge transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If interdigital transducer electrodes are disposed on the piezoelectric substrate, then the elastic wave device can function properly, but polarization reversal occurs due to electric charge generation which increases insertion loss
Solution Approach 1:
The patent extracts the harmful electric charge from the piezoelectric substrate by introducing electrode lands that provide a discharge path. The electrode lands are electrically connected to the IDT electrodes and extend to the side surfaces of the substrate, allowing accumulated charge to be removed through connections to ground potential, thereby preventing polarization reversal while maintaining the functional IDT electrodes.
Solution Approach 2:
The electrode lands serve as an intermediary structure between the IDT electrodes and the substrate side surfaces. These lands provide a controlled path for charge dissipation, mediating the interaction between the functional electrodes and the harmful charge accumulation, thus protecting the substrate from polarization reversal without interfering with the normal operation of the IDT electrodes.
2Reliability
If the piezoelectric substrate is used with conventional electrode configuration, then the device structure is simple, but polarization reversal easily occurs increasing insertion loss
Solution Approach 1:
The electrode system is segmented into functional components (IDT electrodes for signal generation) and protective components (electrode lands for charge management). The electrode lands are divided into multiple segments that extend along the side portions of the substrate, providing distributed charge dissipation paths. This segmentation allows the device to maintain simple overall structure while incorporating effective charge management functionality.
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 significantly reduces or prevents the increase in insertion loss by minimizing polarization reversal and enhancing electric charge transfer, thereby maintaining the piezoelectricity of the substrate.
Implementation Method 1
electric charge due to the piezoelectric effect
Implementation Method 2
electric charge due to the piezoelectric effect or the pyroelectric effect
Data Source
AI summary
An elastic wave device includes a piezoelectric substrate, first and second IDT electrodes on a first main surface, and electrode lands each connected to one of the first and second IDT electrodes. First and second side portions extend in a direction perpendicular or substantially perpendicular to a polarization axis direction and to a direction normal to the piezoelectric substrate. The length of the piezoelectric substrate along the polarization axis direction at the first side portion is shorter than that at the second side portion. The first IDT electrode is closer to the first side portion than the second IDT electrode. The electrode lands include a first electrode land connected to the first busbar of the first IDT electrode without having the second IDT electrode interposed therebetween, and a second electrode land being at the same potential as the first busbar of the first IDT electrode.