Bulk Acoustic Resonator Frame Electrode Design
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Solution Overview
Problem
Bulk acoustic resonators face challenges in achieving a high effective electromechanical coupling coefficient while minimizing spurious noise and maintaining quality factor, particularly due to the trade-off between trapping lateral waves and degrading the coupling coefficient when using ring-shaped electrode layers.
Innovation Solution
The introduction of a frame electrode layer with spaced frame electrodes or alternately formed concave and convex portions along the outer circumference of the active region, which improves the effective electromechanical coupling coefficient and reduces spurious noise by optimizing the length and ratio of these features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a ring-shaped electrode layer is used to trap lateral waves, then spurious noise is reduced, but the effective electromechanical coupling coefficient deteriorates
Solution Approach 1:
The frame electrode layer is divided into multiple frame electrodes spaced apart from each other, creating divided portions between adjacent frame electrodes. This segmentation allows the structure to trap lateral waves effectively while maintaining the electromechanical coupling coefficient by optimizing the ratio of frame electrode length to divided portion length.
Solution Approach 2:
The invention optimizes the geometric parameters of the frame electrode layer, specifically the length of frame electrodes and the spacing between them (divided portions). By controlling the ratio of frame electrode length to divided portion length within 20% to 200%, the patent achieves both lateral wave trapping and high electromechanical coupling coefficient.
2Reliability
If the length of frame electrodes is increased to improve coupling coefficient, then device area increases
Solution Approach 1:
The frame electrodes are positioned only along the outer circumference portion of the active region, not covering the entire area. This partial action approach provides sufficient lateral wave trapping and coupling coefficient improvement without requiring excessive device area, achieving optimal performance with minimal footprint.
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 enhances the square value of the effective electromechanical coupling coefficient and reduces spurious noise, leading to improved resonator efficiency and quality factor performance.
Implementation Method 1
When electric energy is applied to the first and second electrodes to induce an electric field within the piezoelectric layer, the electric field causes a piezoelectric phenomenon in the piezoelectric layer that vibrates the resonating part in a predetermined direction.
Implementation Method 2
As a result, an acoustic wave occurs in the same direction as the vibration direction of the resonating part, to cause resonance.
Data Source
AI summary
A bulk acoustic resonator may include a substrate; a resonating portion including a first electrode layer, a piezoelectric layer, and a second electrode layer which are sequentially stacked on the substrate, and partitioned into an active region and a non-active region; and a frame electrode layer including frame electrodes disposed within the active region to be spaced apart from each other along an outer circumference portion of the active region.