Dual-Step BAW Top Electrodes to Shift BO Modes from Passbands
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bulk acoustic wave (BAW) resonators face challenges in achieving high quality factors and suppressing spurious modes while avoiding undesirable BO modes that interfere with passbands, particularly in high-frequency applications like 5G wireless devices, where filter complexity and size reduction are critical.
Innovation Solution
The design incorporates top electrodes with a dual-step border arrangement, including an inner and outer step, and dielectric spacer layers between the outer steps and the piezoelectric layer, along with passivation layers that extend over or are inset from the peripheral edges, to enhance acoustic impedance mismatch and reduce lateral energy leakage, thereby improving quality factors and shifting BO modes away from passbands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional top electrode structure is used, then the device complexity is low, but the quality factor is reduced due to lateral energy leakage and spurious modes
Solution Approach 1:
The top electrode is segmented into multiple regions with different heights: a central region at the first height, an inner step region at the second height, and an outer step region at the third height. This segmentation creates acoustic impedance mismatches that suppress lateral energy leakage and spurious modes, thereby improving the quality factor without excessive complexity.
Solution Approach 2:
Different portions of the top electrode are given different local properties through the dual-step configuration. The inner step and outer step regions have different heights and acoustic impedances compared to the central region, creating localized acoustic barriers that selectively suppress spurious modes while maintaining low complexity overall.
2Object-generated harmful factors
If border modes are suppressed by increasing electrode mass, then spurious modes are reduced, but the device size and mass increase
Solution Approach 1:
Instead of suppressing spurious modes by increasing mass in the horizontal plane, the invention uses vertical dimensionality by creating a dual-step structure with different heights. The inner step and outer step form acoustic barriers that suppress lateral energy leakage through impedance mismatch in the vertical dimension, achieving spurious mode suppression without increasing overall electrode mass.
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 effectively suppresses spurious modes, increases quality factors, and shifts BO modes farther away from the passbands, leading to improved performance and reduced interference in high-frequency filtering applications, particularly beneficial for 5G wireless devices.
Implementation Method 1
a piezoelectric layer over the bottom electrode
Implementation Method 2
enhance acoustic impedance mismatch and reduce lateral energy leakage
Implementation Method 3
BAW resonators are provided with high quality factors and suppression of spurious modes while also providing weakened BO modes that are shifted farther away from passbands
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.