Raised-Frame BAW Filters for Spurious Mode and Leakage Control
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Solution Overview
Problem
Existing bulk acoustic wave (BAW) devices and filters face challenges in achieving improved performance, particularly in terms of quality factor (Q) and reduced lateral energy leakage, which affects their efficiency in radio frequency applications.
Innovation Solution
The implementation of a bulk acoustic wave device with a raised frame structure, comprising a first raised frame layer with a lower acoustic impedance and a second raised frame layer with a higher acoustic impedance, positioned outside the active region of the device. This configuration reduces lateral energy leakage and enhances the quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional BAW device structure is used, then the device is simple to manufacture, but lateral energy leakage occurs and quality factor is reduced
Solution Approach 1:
The frame structure is divided into multiple segments including a first frame layer, second frame layer, and third frame layer, each with different acoustic impedance characteristics. This segmentation allows each layer to address specific aspects of energy leakage suppression while maintaining manufacturability through modular construction
Solution Approach 2:
Different frame layers are positioned at specific locations around the active region with tailored acoustic impedance properties. The first frame layer has lower acoustic impedance than the active region, the second frame layer has higher acoustic impedance, and the third frame layer has lower acoustic impedance again, creating localized acoustic properties that optimally suppress lateral energy leakage at different depths
2Loss of energy
If no frame structure is used, then the device complexity is low, but lateral energy leakage is not suppressed
Solution Approach 1:
The frame structure employs composite material design with three distinct layers having different acoustic impedance characteristics. This composite structure creates acoustic mismatch at multiple interfaces, effectively blocking lateral energy leakage paths that would otherwise occur in a homogeneous structure
Solution Approach 2:
The frame structure extends vertically with three layers at different depths below the piezoelectric layer, addressing energy leakage suppression in the vertical dimension. This multi-layer vertical arrangement creates acoustic barriers at different depths, preventing energy leakage that propagates laterally at various vertical positions
3Reliability
If a single-layer frame structure is used, then the manufacturing is simpler, but spurious modes are not effectively suppressed
Solution Approach 1:
The frame is segmented into three functional layers with alternating acoustic impedance characteristics. This segmentation creates multiple acoustic reflection interfaces that target different spurious mode frequencies and propagation paths, providing comprehensive suppression that a single layer cannot achieve
Solution Approach 2:
The second frame layer with higher acoustic impedance acts as an intermediary barrier between the active region and the outer environment. This intermediate layer with contrasting acoustic properties creates additional reflection interfaces that enhance spurious mode suppression while the outer first and third layers provide further acoustic isolation
4Loss of energy
If the frame structure extends too far inward, then lateral energy leakage is better suppressed, but the active region is reduced
Solution Approach 1:
Instead of extending the frame horizontally into the active region, the solution extends vertically with three layers at different depths. This vertical dimensionality change allows the frame to suppress lateral energy leakage that propagates at different vertical levels without horizontally encroaching on the active region area
Solution Approach 2:
Each frame layer is positioned at a specific vertical location with optimized dimensions for its depth. The first frame layer is positioned closer to the active region with specific width, the second layer extends further with different dimensions, and the third layer provides outer containment. This localized positioning at different depths maximizes leakage suppression while preserving active region area
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 raised frame structure effectively suppresses spurious modes, improves the quality factor above the resonant frequency, and maintains low insertion loss and Gamma loss, thereby enhancing the performance of BAW devices and filters.
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.