Raised-Frame BAW Resonators for Spurious Mode Suppression
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Solution Overview
Problem
Current bulk acoustic wave (BAW) devices face challenges in achieving high quality factor (Q) and low insertion loss, particularly due to lateral energy leakage and spurious modes that degrade performance, especially in carrier aggregation bands.
Innovation Solution
The implementation of a raised frame structure with a low acoustic impedance material, such as silicon dioxide, and a high acoustic impedance material, like molybdenum or tungsten, in a dual-layer configuration, where the first raised frame layer extends further inward than the second, to suppress spurious modes and enhance Q by reducing lateral energy leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a raised frame structure is added to suppress lateral energy leakage, then quality factor (Q) is improved, but device complexity increases
Solution Approach 1:
The raised frame structure is divided into multiple layers (first raised frame layer and second raised frame layer) with different acoustic impedances. Each layer serves a specific function: the first layer (lower acoustic impedance) primarily suppresses lateral energy leakage, while the second layer (higher acoustic impedance) targets spurious modes. This segmentation allows the complex structure to address multiple performance issues simultaneously while maintaining manufacturability through standardized layering approaches.
Solution Approach 2:
The raised frame structure employs composite material design by combining materials with different acoustic impedance characteristics. The first raised frame layer uses a material with lower acoustic impedance than the piezoelectric layer, while the second layer uses a material with higher acoustic impedance. This composite approach creates acoustic impedance contrast that effectively reflects lateral energy and suppresses spurious modes, thereby improving quality factor without requiring excessive structural complexity.
2Reliability
If the first raised frame layer extends further inward than the second raised frame layer, then spurious modes are suppressed, but manufacturing precision requirements increase
Solution Approach 1:
The raised frame structure implements local quality differentiation by extending the first raised frame layer further inward than the second raised frame layer. This creates a stepped configuration where each layer has a different radial extent. The first layer's greater inward extension specifically targets regions where lateral energy leakage occurs, while the second layer provides broader coverage for spurious mode suppression. This localized differentiation optimizes performance without requiring ultra-precise manufacturing, as the stepped design accommodates typical fabrication tolerances.
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 achieves improved Q factors both below and above the resonant frequency, reducing Gamma loss and spurious mode effects, thereby enhancing the performance of BAW filters in radio frequency applications.
Implementation Method 1
The second raised frame layer can have a higher acoustic impedance than the first raised frame layer
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.