Overtone BAW Resonator Structure for High-Frequency Filtering
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Solution Overview
Problem
Achieving high resonant frequencies in bulk acoustic wave (BAW) resonators for filtering higher frequency radio frequency signals is challenging due to technical issues such as smaller size leading to lower quality factors, increased edge energy leakage, reduced power handling, and manufacturing difficulties with thinner piezoelectric layers.
Innovation Solution
The use of an overtone mode as the main mode in BAW devices, with a combination of a piezoelectric layer and a temperature compensation layer, where the total thickness is sufficient to excite the overtone mode, providing better power handling and temperature compensation, and adjusting the thickness of the temperature compensation layer to control the resonant frequency and electromechanical coupling coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the piezoelectric layer is made thinner to achieve higher resonant frequency, then the resonant frequency increases, but the quality factor decreases and edge energy leakage increases
Solution Approach 1:
The patent introduces a temperature compensation layer as an additional dimensional element in the device structure. This layer has a positive temperature coefficient of frequency that compensates for the negative temperature coefficient of the piezoelectric layer, thereby stabilizing the overall resonant frequency and improving device reliability at higher frequencies without requiring the piezoelectric layer to be excessively thin
2Speed
If the piezoelectric layer is made thinner to achieve higher resonant frequency, then the resonant frequency increases, but power handling capability is reduced
Solution Approach 1:
The patent creates a composite structure by combining the piezoelectric layer with a temperature compensation layer. This composite material system allows the device to operate at higher resonant frequencies while the combined structure maintains improved power handling capability compared to using a thin piezoelectric layer alone
3Speed
If the piezoelectric layer is made thinner to achieve higher resonant frequency, then the resonant frequency increases, but manufacturing precision becomes more difficult
Solution Approach 1:
The temperature compensation layer serves as an intermediary element that simplifies the manufacturing process. By adding this layer, the device can achieve higher resonant frequencies without requiring the piezoelectric layer to be extremely thin, thus avoiding the manufacturing precision challenges associated with thin film deposition and handling
4Reliability
If the temperature compensation layer thickness is increased to improve temperature compensation, then temperature coefficient of frequency is reduced, but device complexity increases
Solution Approach 1:
The patent optimizes the thickness parameter of the temperature compensation layer to achieve effective temperature compensation. By carefully selecting the thickness within specific ranges, the device achieves reduced temperature coefficient of frequency while maintaining reasonable device complexity and avoiding excessive layer thickness
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 approach allows for higher resonant frequencies with fewer spurious modes, improved power handling, and reduced temperature coefficient of frequency variation, enabling effective filtering of higher frequency ranges such as those in 5G New Radio applications.
Implementation Method 1
In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer
Implementation Method 2
at least one temperature compensation layer positioned between the first and second electrodes
Data Source
AI summary
A bulk acoustic wave device that is configured to excite an overtone mode as a main mode is disclosed. The bulk acoustic wave device can include a first electrode, a piezoelectric layer, a second electrode, and at least one temperature compensation layer. The piezoelectric layer is positioned over the first electrode. The second electrode is positioned such that the piezoelectric layer is located between the first and second electrodes. The at least one temperature compensation layer is configured to provide temperature compensation for the bulk acoustic wave device. The at least one temperature compensation layer has a thickness that is a multiple of one thirty-second of a wavelength of an acoustic wave propagating through the at least one temperature compensation layer. The bulk acoustic wave device is configured to excite the overtone mode as the main mode.