BAW Resonator Border Ring Layout for Spurious Mode Suppression
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Solution Overview
Problem
Bulk Acoustic Wave (BAW) resonators face challenges in suppressing spurious modes, particularly below the series resonance frequency, which affects their quality factor and performance in high-frequency filter applications.
Innovation Solution
The introduction of an electrically isolated Border (BO) ring in BAW resonators, which includes a non-conductive and conductive portion, is used to suppress spurious modes above and below the series resonance frequency, improving the resonator's performance by optimizing the BO ring's dimensions and materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional BAW resonator structure is used, then the device is simple to manufacture, but spurious modes cannot be effectively suppressed below the series resonance frequency
Solution Approach 1:
The top electrode is segmented into two distinct portions: a first portion that is electrically connected to the bottom electrode through the piezoelectric layer, and a second portion (border ring) that is electrically isolated from the first portion. This segmentation allows the border ring to suppress spurious modes independently while the first portion maintains the primary resonant function, thereby resolving the contradiction between suppressing spurious modes and maintaining structural simplicity.
Solution Approach 2:
A non-conductive layer is introduced as an intermediary between the first portion and the second portion of the top electrode. This non-conductive layer electrically isolates the border ring from the main electrode while allowing both to coexist on the piezoelectric layer, enabling spurious mode suppression without requiring complex reconfiguration of the electrode structure.
2Reliability
If the top electrode is extended to suppress spurious modes, then spurious mode suppression improves, but parasitic capacitance increases
Solution Approach 1:
The top electrode is divided into a first portion and a second portion (border ring) that are electrically isolated from each other. The border ring can be optimized for spurious mode suppression with minimal area, while the first portion is optimized for electrical connection. This segmentation allows independent optimization of each portion, suppressing spurious modes effectively while minimizing the area of conductive material and thus reducing parasitic capacitance.
Solution Approach 2:
The border ring is positioned specifically at the periphery of the piezoelectric layer where spurious modes tend to concentrate. By concentrating the spurious mode suppression function in this specific location rather than extending the top electrode uniformly, the design achieves effective suppression with minimal additional conductive material, thereby reducing parasitic capacitance.
3Reliability
If a larger top electrode area is used, then spurious mode suppression is improved, but the resonator size increases
Solution Approach 1:
The top electrode structure is segmented into a first portion and a second portion (border ring) that are electrically isolated. The border ring is positioned at the periphery and can be optimized to provide maximum spurious mode suppression with minimal area. This segmentation allows the resonator to achieve effective spurious mode suppression without requiring a large overall electrode area, thus maintaining compact dimensions.
Solution Approach 2:
Instead of extending the top electrode uniformly across the entire piezoelectric layer, the border ring is applied partially only at the periphery where it is most effective for suppressing spurious modes. This partial application achieves the necessary suppression function with minimal additional area, avoiding the need for a large overall resonator structure.
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 electrically isolated BO ring effectively suppresses spurious modes across the entire frequency range, enhancing the quality factor and coupling coefficients of BAW resonators, leading to improved filtering performance and reduced parasitic capacitances.
Implementation Method 1
a piezoelectric layer over the bottom electrode and having a top surface with a first portion and second portion about the first portion
Implementation Method 2
the BO ring has a conductive portion over the non-conductive portion. In these embodiments, the conductive portion is electrically isolated from the top electrode. Furthermore, the BAW resonator resonates at a series resonant frequency (fs) and has no BO mode below the series resonant frequency (fs)
Data Source
AI summary
A Bulk Acoustic Wave (BAW) resonator with an electrically isolated Border (BO) ring is provided. One BAW resonator includes a bottom electrode and a piezoelectric layer over the bottom electrode and having a top surface with a first portion and second portion about the first portion. The BAW resonator also includes a top electrode over the first portion of the piezoelectric layer and a BO ring including a non-conductive portion that is over the second portion of the piezoelectric layer and adjacent to the piezoelectric layer. The BAW resonator may be a Solidly Mounted BAW (SMR-BAW) resonator or a Film BAW Resonator (FBAR). A radio frequency filter including a ladder configuration with the above BAW resonator as a series BAW resonator and methods for fabricating the above BAW resonator are also provided.