FBAR Reflection Cavity Structure for Parasitic Mode Suppression
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Solution Overview
Problem
Existing film bulk acoustic wave resonators face challenges in effectively reducing transverse parasitic modes and acoustic wave leakage, which are crucial for improving the quality factor and performance of radio-frequency filters, especially as technology advances.
Innovation Solution
The design incorporates a substrate with a bottom electrode featuring a first arched part forming a cavity, a piezoelectric layer, and a top electrode with arched parts, including reflection cavities in the periphery of the effective working area to reflect transverse acoustic waves, along with an air gap formed by a recessed second cavity, optimizing the thickness and arrangement to reduce stress and enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reflection cavity is only designed in the top electrode at the periphery, then the structure is simple, but the transverse parasitic mode and acoustic wave leakage are not effectively reduced
Solution Approach 1:
The reflection cavity is segmented into multiple parts: a first reflection cavity in the bottom electrode and a second reflection cavity in the top electrode. This segmentation allows each cavity to work independently to reflect acoustic waves from different directions, effectively reducing transverse parasitic modes and acoustic wave leakage while maintaining reasonable structural complexity
Solution Approach 2:
The first and second reflection cavities are nested in a complementary manner, with the first cavity positioned at the bottom electrode periphery and the second cavity at the top electrode periphery. This nested arrangement creates a comprehensive acoustic wave reflection system that addresses limitations of single-cavity designs
2Reliability
If the arched part thickness is increased to improve acoustic wave reflection, then the reflection performance improves, but stress concentration and potential cracking increase
Solution Approach 1:
The arched part is designed with non-uniform thickness distribution, having different thicknesses at different locations. The thickness is optimized to provide sufficient acoustic wave reflection performance while avoiding excessive thickness that would cause stress concentration and cracking
Solution Approach 2:
The arched part采用 curved geometry instead of flat structure, which helps distribute stress more evenly throughout the structure. The curved shape provides effective acoustic wave reflection while reducing stress concentration compared to sharp angular designs
3Power
If the effective working area is maximized to improve resonator performance, then the output signal increases, but acoustic wave leakage increases
Solution Approach 1:
The arched part with reflection cavities acts as an intermediary structure between the effective working area and the substrate. It reflects acoustic waves that would otherwise leak into the substrate, thereby maintaining a large effective working area for high output signal while preventing acoustic wave leakage
Solution Approach 2:
The reflection cavities are positioned in the peripheral region, creating a dimensional boundary that separates the effective working area from the substrate. This peripheral positioning allows acoustic wave reflection without reducing the central effective working area, thus maintaining high output signal while preventing 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 effectively reduces transverse parasitic modes and acoustic wave leakage, improving the quality factor and reliability of the film bulk acoustic wave resonator while preventing stress-related issues in the arched parts, thus enhancing the overall performance and stability of the resonator.
Implementation Method 1
a piezoelectric layer and a top electrode which are located on an upper surface of the substrate
Implementation Method 2
a first reflection cavity is formed between the bottom electrode and the piezoelectric layer and located in a slope of the first arched part
Data Source
AI summary
The present disclosure provides a film bulk acoustic wave resonator and a preparation method thereof, and relates to the technical field of semiconductors. The film bulk acoustic wave resonator includes a substrate and a bottom electrode, a piezoelectric layer and a top electrode which are located on an upper surface of the substrate, the bottom electrode is provided with a first arched part so as to form a first cavity between the first arched part and the substrate; and a first reflection cavity is formed between the bottom electrode and the piezoelectric layer and located in a slope of the first arched part, the bottom electrode is provided with the first arched part and the first reflection cavity may be located in an oblique plane of the slope of the first arched part.