Dual-Layer Raised Frame BAW Filters for Spurious Mode Suppression
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Solution Overview
Problem
Existing bulk acoustic wave (BAW) devices face challenges in achieving high quality factor (Q) and low insertion and Gamma losses, particularly due to lateral energy leakage and spurious modes that degrade performance, especially in carrier aggregation applications.
Innovation Solution
The BAW devices incorporate a dual-layer raised frame structure with a low acoustic impedance first layer, such as silicon dioxide, and a higher impedance second layer, extending further inward than the first layer, to suppress spurious modes and improve Q, while maintaining low loss characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional single-layer raised frame structure is used, then the device structure is simple, but lateral energy leakage occurs and spurious modes are generated, degrading the quality factor
Solution Approach 1:
The raised frame structure is divided into multiple layers with different acoustic impedances. The first raised frame layer has a first acoustic impedance and the second raised frame layer has a second acoustic impedance that is higher than the first, creating a segmented structure that better controls acoustic wave propagation and reduces spurious modes while maintaining manufacturability
Solution Approach 2:
The raised frame structure uses composite material layers with different acoustic impedance properties. By combining materials with different acoustic characteristics (first raised frame layer with lower impedance, second raised frame layer with higher impedance), the structure achieves superior acoustic confinement and spurious mode suppression compared to single-material frames
2Reliability
If the raised frame structure extends further inward, then spurious modes are better suppressed, but the device area increases
Solution Approach 1:
The raised frame structure is configured with different extension distances for different layers: the first raised frame layer extends a first distance inward from the perimeter, while the second raised frame layer extends a second distance inward that is less than the first distance. This local variation in structure provides effective spurious mode suppression at critical locations while minimizing overall area increase
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 dual-layer raised frame structure enhances Q and reduces insertion and Gamma losses, effectively managing spurious modes and maintaining high performance across resonant frequencies, particularly in carrier aggregation bands.
Implementation Method 1
The second raised frame layer can have a higher acoustic impedance than the first raised frame layer
Implementation Method 2
a piezoelectric layer between the first electrode and the second electrode
Data Source
AI summary
Aspects of this disclosure relate to bulk acoustic wave devices that have a raised frame structure, and filters that utilize the bulk acoustic wave devices. The raised frame structure can include a first raised frame layer that has a relatively low acoustic impedance. The raised frame structure can include a second raised frame layer that has a relatively high acoustic impedance. The first raised frame layer can extend inward further than the second raised frame layer. A width of the first raised frame layer that overlaps the first and second electrodes is between about 1.5 times to about 4 times larger than the combined thickness of the first electrode, the piezoelectric layer, and the second electrode.