Stepped BAW Top Electrodes With Dielectric Spacers for BO Modes
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators face challenges in achieving high quality factors and suppressing spurious modes, particularly due to the introduction of border (BO) modes that can interfere with passbands and increase insertion loss in high-frequency applications.
Innovation Solution
The implementation of top electrodes with a dual-step border arrangement, including an inner and outer step, along with dielectric spacer layers and passivation layers, which helps in suppressing spurious modes and shifting BO modes away from the passbands, thereby enhancing the quality factor and reducing lateral energy leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional top electrode structure is used, then the device complexity is low, but spurious modes are not suppressed and quality factor is reduced
Solution Approach 1:
The top electrode is segmented into multiple regions with different heights: a central region at the base level, an inner step region elevated above the base, and an outer step region at the highest level. This segmentation creates distinct acoustic impedance zones that suppress spurious modes while maintaining the piezoelectric effect for signal generation.
Solution Approach 2:
Different regions of the top electrode are given different local properties through varying heights. The inner step region provides mass loading for mode suppression, while the outer step region creates acoustic impedance mismatch. This local differentiation allows simultaneous optimization of quality factor and spurious mode suppression in specific areas.
2Object-generated harmful factors
If border modes are suppressed to improve passband performance, then insertion loss increases due to lateral energy leakage
Solution Approach 1:
Dielectric spacer layers are introduced as intermediary elements between the top electrode steps and the piezoelectric layer. These spacers provide acoustic isolation that prevents lateral energy leakage into border modes while maintaining the beneficial mass loading and impedance effects. The spacers act as mediators that decouple the electrode structure from direct acoustic coupling with the piezoelectric layer edges.
3Ease of manufacture
If the top electrode covers the entire piezoelectric layer, then manufacturing is simpler, but lateral energy leakage increases and quality factor decreases
Solution Approach 1:
The solution moves from a two-dimensional planar electrode layout to a three-dimensional stepped structure with varying heights. By adding the vertical dimension, the electrode can provide both full coverage for manufacturing simplicity and localized impedance control for quality factor enhancement. The stepped configuration creates acoustic reflection planes that prevent lateral energy leakage.
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 spurious modes, allowing for more effective filtering in high-frequency applications while minimizing interference and maintaining low insertion loss.
Implementation Method 1
a piezoelectric layer that is arranged between top and bottom electrodes
Implementation Method 2
a dielectric spacer layer arranged between the outer step and the piezoelectric layer
Data Source
AI summary
Bulk acoustic wave (BAW) resonators and particularly top electrodes with step arrangements for BAW resonators are disclosed. Top electrodes on piezoelectric layers are disclosed that include a border (BO) region with a dual-step arrangement where an inner step and an outer step are formed with increasing heights toward peripheral edges of the top electrode. Dielectric spacer layers may be provided between the outer steps and the piezoelectric layer. Passivation layers are disclosed that extend over the top electrode either to peripheral edges of the piezoelectric layer or that are inset from peripheral edges of the piezoelectric layer. Piezoelectric layers may be arranged with reduced thickness portions in areas that are uncovered by top electrodes. BAW resonators as disclosed herein are provided with high quality factors and suppression of spurious modes while also providing weakened BO modes that are shifted farther away from passbands of such BAW resonators.