BAW Resonator Dual-Step Oxide Ring for BO Mode Suppression
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators face challenges in achieving high quality factors and suppressing spurious modes and BO modes, which affect their performance in high-frequency applications, particularly in 5G wireless devices, due to the introduction of undesirable modes and energy leakage.
Innovation Solution
A dual-step oxide border ring structure is implemented over the piezoelectric layer, featuring an inner and outer ring with varying heights and widths, and transition sections to create acoustic impedance mismatch and reduce electric fields, thereby enhancing the quality factor and suppressing BO modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-layer border ring structure is used, then the device complexity is low, but the quality factor is insufficient and spurious modes are not effectively suppressed
Solution Approach 1:
The border ring structure is segmented into multiple layers with different heights. The first border ring layer has a first height and the second border ring layer has a second height greater than the first height, creating a stepped configuration. This segmentation allows each layer to contribute differently to acoustic wave management, improving quality factor and suppressing spurious modes through cumulative effect while maintaining manageable structural complexity.
Solution Approach 2:
The invention adds a vertical dimension to the border ring structure by creating layers at different heights. The stepped configuration introduces height variation as an additional dimensional parameter, transforming a planar two-dimensional structure into a three-dimensional stepped structure. This dimensional change enables better acoustic impedance management and more effective suppression of spurious modes.
2Reliability
If the border ring structure height is increased uniformly, then acoustic impedance mismatch improves, but lateral energy leakage increases due to abrupt height changes
Solution Approach 1:
Different regions of the border ring structure are assigned different local qualities through the stepped configuration. The first border ring layer provides a baseline acoustic impedance, while the second border ring layer at greater height provides enhanced acoustic impedance in specific regions. This local quality variation optimizes acoustic impedance mismatch without requiring uniform height increase throughout the entire structure, thereby reducing lateral energy leakage.
Solution Approach 2:
The border ring structure employs asymmetric height distribution with the second border ring layer having greater height than the first border ring layer. This asymmetric stepped configuration creates optimal acoustic impedance transitions in specific regions where they are most needed for suppressing spurious modes, while maintaining lower heights in other regions to minimize lateral energy leakage.
3Reliability
If a dual-step oxide border ring structure is implemented, then spurious modes are suppressed and quality factor improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The invention changes the height parameter of the oxide border ring structure by implementing two distinct layers with different heights. The first border ring layer has a first height and the second border ring layer has a second height greater than the first height. This parameter change enables effective spurious mode suppression through optimized acoustic impedance transitions while using the same oxide material, avoiding the need for complex multi-material fabrication processes.
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-step oxide border ring structure significantly improves the quality factor of BAW resonators by reducing lateral energy leakage and suppressing BO modes, making them more suitable for high-frequency applications with reduced insertion loss and interference.
Implementation Method 1
a dual-step oxide border (BO) ring structure... such that the dual-step BO structure decreases in height toward the central portion of the piezoelectric layer... creates acoustic impedance mismatch and reduce electric fields
Implementation Method 2
a piezoelectric layer over the bottom electrode... Bulk acoustic wave (BAW) resonators
Data Source
AI summary
The present disclosure relates to a bulk acoustic wave (BAW) resonator that includes a bottom electrode, a piezoelectric layer over the bottom electrode, and a top electrode structure with a top electrode and the dual-step BO ring structure. Herein, the dual-step BO structure is formed over the piezoelectric layer and about a periphery of the top electrode structure, such that a central portion of the piezoelectric layer is not covered by the dual-step BO structure. The dual-step BO structure is formed of an oxide material and includes an inner BO ring with a first height and an outer BO ring with a second height that is larger than the first height, such that the dual-step BO structure decreases in height toward the central portion of the piezoelectric layer. The top electrode is formed over the central portion of the piezoelectric layer and extends over the dual-step BO structure.