BAW Resonator Bragg Mirror Layout for BO Mode Suppression
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators face challenges in balancing quality factor and BO mode suppression, with existing border ring (BO) structures either introducing undesirable modes or failing to suppress spurious modes effectively, which affects the performance and design of high-frequency filters.
Innovation Solution
A BAW resonator design incorporating a border ring (BO) structure with a dual-step configuration and a leaky reflector, where high acoustic impedance layers are strategically embedded in a low acoustic impedance region, allowing BO modes to leak into the substrate, thereby suppressing BO modes, and maintaining a high quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a border ring (BO) structure is added to suppress spurious modes, then filter performance is improved, but the BO structure may introduce undesirable BO modes
Solution Approach 1:
The patent extracts the harmful BO modes from the resonator system by introducing a leaky reflector structure that allows these modes to leak into the substrate. The reflector includes high acoustic impedance layers embedded in a low acoustic impedance region, creating a mechanism to remove unwanted acoustic energy from the active resonator region.
Solution Approach 2:
The leaky reflector acts as an intermediary element between the resonator and the substrate. It mediates the interaction by providing a controlled path for BO modes to escape into the substrate while maintaining the resonator's quality factor through strategic placement of high acoustic impedance layers.
2Object-generated harmful factors
If high acoustic impedance layers are extended through the BO region to suppress BO modes, then BO mode suppression is improved, but the quality factor decreases
Solution Approach 1:
The patent applies local quality by making the first high acoustic impedance layer's width smaller than the top electrode structure's width, creating a localized region of high acoustic impedance that does not extend completely through the BO region. This localized approach suppresses BO modes in critical areas while preserving the quality factor in other regions.
Solution Approach 2:
Instead of extending the high acoustic impedance layer fully through the BO region, the patent uses partial action by positioning the layer such that it does not completely traverse the BO region. This partial extension is sufficient to suppress BO modes while avoiding the quality factor degradation that would result from full extension.
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 proposed design effectively suppresses BO modes while maintaining a high quality factor, enhancing the performance of BAW resonators for wide bandwidth filtering and multiplexing applications by optimizing the alignment and extension of high acoustic impedance layers within the BO region.
Implementation Method 1
a leaky reflector with a first high acoustic impedance layer and a second high acoustic impedance layer embedded in a low acoustic impedance region
Implementation Method 2
allowing BO modes to leak into the substrate, thereby suppressing BO modes
Implementation Method 3
a piezoelectric layer over the bottom electrode
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
The present disclosure relates to a bulk acoustic wave, BAW, resonator (36) that includes a bottom electrode (48), a top electrode structure (44) with a border ring, BO, structure (56), a piezoelectric layer (42) sandwiched between the bottom electrode (48) and the top electrode (58), and a reflector (38) with a high acoustic impedance layer (80-1,80-2) embedded in a low acoustic impedance region (78). Herein, the BO structure (56) is formed about a periphery of the top electrode structure (44) and defines a BO region (66) of the BAW resonator (36). The first high acoustic impedance layer (80-1) is vertically underneath the bottom electrode (48) and is separated from the bottom electrode (48) by a first portion of the low acoustic impedance region (78-1). A width (WFH) of the first high acoustic impedance layer (80-1) is smaller than a width (WTE) of the top electrode structure (44), such that the first high acoustic impedance layer (80-1) does not extend completely through the BO region (66) of the BAW resonator (36).