Shaped BAW Border Rings for Spurious 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 while minimizing acoustic leakage and mode conversion, particularly due to the introduction of BO modes that can restrict design and performance in wide bandwidth filtering applications.
Innovation Solution
The implementation of a shaped border (BO) ring in BAW resonators, where the top surface of the BO ring is graded in a descending manner towards the central region, reducing acoustic leakage and mode conversion, and incorporating a mass-reducing inner ring to suppress spurious modes, thereby enhancing the quality factor and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional planar top electrode is used, then the device structure is simple, but acoustic leakage and mode conversion occur leading to reduced quality factor
Solution Approach 1:
The top electrode is divided into distinct regions with different heights: a central region at a first height, a border ring at a second height, and an outer ring at a third height. Each region serves a specific function in controlling acoustic wave behavior, with the border ring region specifically designed to suppress spurious modes while the central region maintains primary resonator function.
Solution Approach 2:
The electrode structure transitions from a two-dimensional planar configuration to a three-dimensional stepped configuration with multiple height levels. This vertical dimensionality addition creates distinct acoustic impedance zones that effectively suppress lateral acoustic leakage and mode conversion without complicating the lateral footprint.
2Reliability
If a border ring is added to suppress spurious modes, then quality factor improves, but acoustic leakage increases due to BO modes
Solution Approach 1:
The border ring height is specifically optimized to create a height difference that generates acoustic impedance mismatch, reflecting acoustic waves back into the active region. The height parameter is tuned to suppress spurious modes while minimizing the generation of border ring modes that could cause acoustic leakage.
Solution Approach 2:
The border ring acts as an intermediary acoustic impedance layer between the high-acoustic-impedance piezoelectric layer and the low-acoustic-impedance surrounding medium. This intermediate structure provides gradual acoustic impedance transition, reducing acoustic leakage while maintaining spurious mode suppression.
3Reliability
If the top electrode mass is reduced to improve frequency response, then spurious modes are suppressed, but the quality factor decreases due to increased acoustic leakage
Solution Approach 1:
The top electrode implements local mass variation through the stepped structure: the central region maintains sufficient mass for strong acoustic coupling and high quality factor, while the border ring region has reduced mass to suppress spurious modes. This localized mass optimization achieves both goals simultaneously.
Solution Approach 2:
The top electrode is segmented into multiple functional zones with different masses: a central region with higher mass for primary resonance, and border/outer regions with reduced mass for spurious mode suppression. This segmentation allows independent optimization of each region's mass characteristics.
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 results in improved quality factors and reduced acoustic leakage, effectively suppressing spurious modes and enhancing the performance of BAW resonators for high-frequency applications, particularly in 5G wireless devices.
Implementation Method 1
a piezoelectric layer over the bottom electrode
Implementation Method 2
a top surface of the BO ring forms a height from the piezoelectric layer that is graded in a descending manner from a lateral edge of the BO ring toward the central region
Implementation Method 3
BAW resonators as disclosed herein are provided with high quality factors and suppression of spurious modes
Data Source
AI summary
Bulk acoustic wave (BAW) resonators, and particularly shaped border (BO) rings for BAW resonators are disclosed. Top electrode arrangements are disclosed that include a BO ring arranged about a periphery of a top electrode, where the BO ring forms a top surface having a shape that is sloped or graded in comparison to planar surfaces of the top electrode. The top surface of the BO ring may be arranged such that a height of the top surface is graded in a descending manner toward a central region of the BAW resonator. BAW resonators as disclosed herein are provided with high quality factors and suppression of spurious modes while also providing reduced acoustic leakage and mode conversion.