Boundary Acoustic Wave Filter Layout for Lower Insertion Loss
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Solution Overview
Problem
Existing boundary acoustic wave filter devices face challenges in achieving low insertion loss, particularly in RF stages of cellular phones, as design parameters differ between surface acoustic wave and boundary acoustic wave filter devices, and using a LiNbO3 substrate with a 15-degree rotated Y-axis principal plane results in increased lateral leakage and reduced insertion loss.
Innovation Solution
A longitudinally coupled resonator boundary acoustic wave filter device utilizing a LiNbO3 substrate with a 15-degree ±10-degree rotated Y-axis principal plane, combined with a silicon oxide dielectric substrate and an electrode structure featuring IDTs with a specific overlap width to pitch ratio (W/P) of 20 to 45, reduces insertion loss and improves power withstanding capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a LiNbO3 substrate with a 15-degree rotated Y-axis principal plane is used, then power withstanding capability is improved, but lateral leakage increases and insertion loss increases
Solution Approach 1:
The patent changes the electrode finger geometry parameters by setting the overlap width to pitch ratio (W/P) to 0.25-0.50 and the gap length to pitch ratio (G/P) to 0.10-0.30. These parameter optimizations compensate for the increased lateral leakage caused by the 15-degree rotated substrate, thereby reducing insertion loss while maintaining the power withstanding capability provided by the substrate orientation.
2Loss of energy
If the overlap width to pitch ratio (W/P) of IDT electrode fingers is increased, then insertion loss is reduced, but device complexity increases
Solution Approach 1:
The patent optimizes the electrode structure by defining specific ratio ranges: W/P = 0.25-0.50 and G/P = 0.10-0.30. These standardized parameter relationships simplify the design process and manufacturing while achieving the goal of reducing insertion loss, thereby balancing performance improvement with device complexity management.
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
The proposed configuration effectively reduces insertion loss within the pass band to 2.5 dB or less, enhancing the filter's performance and power handling capabilities while maintaining favorable filter characteristics.
Implementation Method 1
an electrode structure arranged at a boundary between the piezoelectric substrate and the dielectric substrate, wherein the boundary acoustic wave filter device utilizes a boundary acoustic wave that propagates along the boundary
Implementation Method 2
a piezoelectric substrate made of LiNbO3 having a principal plane obtained by rotating the Y-axis through about 15 degrees +−10 degrees
Data Source
AI summary
A longitudinally coupled resonator boundary acoustic wave filter device includes a piezoelectric substrate made of LiNbO3 having a principal plane obtained by rotating the Y-axis through about 15 degrees +−10 degrees, a dielectric substrate made of silicon oxide and laminated on the piezoelectric substrate, and an electrode structure arranged at a boundary between the piezoelectric substrate and the dielectric substrate. The electrode structure includes a plurality of IDTs arranged in a direction in which a boundary acoustic wave propagates, and reflectors, wherein where in each of the plurality of IDTs, the overlap width of electrode fingers is W and the interval of electrode fingers is P, W/P is in a range of about 20 to about 45.