Coupled BAW Resonator Structure for Higher-Order Mode Coupling
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Solution Overview
Problem
Bulk acoustic wave (BAW) resonators attempting to operate in higher order modes experience poor electromechanical coupling, which is lower than that of fundamental mode devices, limiting their performance at high frequencies.
Innovation Solution
Incorporating a coupler layer between two piezoelectric layers with opposing polarities, increasing the electromechanical coupling coefficient by enhancing the acoustic impedance and stress profile integral.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If BAW resonators operate in higher order modes to achieve higher frequency operation, then the operating frequency is improved, but the electromechanical coupling coefficient deteriorates
Solution Approach 1:
The piezoelectric layer is divided into multiple discrete piezoelectric layers (first piezoelectric layer, second piezoelectric layer, etc.) with different polarities. This segmentation allows each layer to contribute differently to the overall stress profile, enabling higher order mode operation while maintaining strong electromechanical coupling through optimized distribution of piezoelectric material throughout the resonator thickness.
Solution Approach 2:
Different regions of the resonator are assigned different piezoelectric layers with specific polarities oriented to maximize stress in particular zones. The first piezoelectric layer has polarity oriented to produce stress in one direction while the second piezoelectric layer has opposite polarity to produce stress in the opposite direction, creating a tailored stress profile that enhances coupling in higher order modes.
2Reliability
If a single piezoelectric layer is used in fundamental mode, then the electromechanical coupling is maximized, but the operating frequency is limited
Solution Approach 1:
The invention transitions from a single-layer fundamental mode structure to a multi-layer higher order mode structure, effectively utilizing the thickness dimension more efficiently. By stacking multiple piezoelectric layers with alternating polarities, the resonator can support higher order modes that fit more wavelength cycles within the same physical thickness, thereby achieving higher operating frequencies while maintaining coupling.
Solution Approach 2:
The resonator employs a composite structure with multiple piezoelectric layers of different polarities rather than a single homogeneous piezoelectric layer. This composite approach allows the different layers to work together to create a stress profile optimized for higher order modes, combining the advantages of multiple materials and configurations to achieve both high frequency and strong coupling.
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 coupler layer significantly improves the electromechanical coupling coefficient of the second overmode BAW resonator, enabling higher frequency operation while maintaining reasonable quality factor and size, making it suitable for high-frequency applications.
Implementation Method 1
The first piezoelectric layer has a first polarity. The second piezoelectric layer has a second polarity opposite the first polarity.
Implementation Method 2
Providing the coupler layer between the first piezoelectric layer and the second piezoelectric layer increases an electromechanical coupling coefficient of the acoustic resonator
Data Source
AI summary
An acoustic resonator includes a first piezoelectric layer, a second piezoelectric layer, a coupler layer, a first electrode, and a second electrode. The first piezoelectric layer has a first polarity. The second piezoelectric layer has a second polarity opposite the first polarity. The coupler layer is between the first piezoelectric layer and the second piezoelectric layer. The first electrode is on the first piezoelectric layer opposite the coupler layer. The second electrode is on the second piezoelectric layer opposite the coupler layer.