Stacked Crystal Filter Structure for Wider Spurious-Free Range
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Solution Overview
Problem
Acoustic filters, such as stacked crystal filters (SCFs), face limitations in operating bandwidth due to spurious resonances and modes, which are difficult to suppress simultaneously with a single reflector structure, especially as mobile communication systems require higher integration and larger bandwidths.
Innovation Solution
Incorporating acoustically soft materials in specific locations corresponding to high stress regions within SCF structures, particularly increasing the thickness and stiffness parameters of shared electrodes and additional layers, to enhance the frequency spread between first and second order modes, thereby increasing the spurious free range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reflector structures with multiple reflector layers are used to suppress spurious responses, then filter rejection performance is improved, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent extracts the spurious response suppression function from the reflector structures and relocates it to the piezoelectric layers. By introducing acoustically soft materials with specific impedance values into the piezoelectric layers at positions corresponding to spurious resonance antinodes, the suppression function is separated from the reflector structures, simplifying them while maintaining rejection performance.
Solution Approach 2:
The patent applies local quality by introducing acoustically soft materials only at specific locations within the piezoelectric layers where spurious resonance antinodes occur. This localized modification targets only the problematic frequencies while leaving the rest of the structure unchanged, thereby suppressing spurious responses without requiring complex modifications to the entire reflector structure.
2Adaptability or versatility
If multiple SCF structures with different frequencies are used to cover broader bandwidth, then operating bandwidth is improved, but spurious responses from multiple SCFs cannot be suppressed simultaneously by a single reflector structure
Solution Approach 1:
The patent makes the piezoelectric layers universal by enabling them to perform both the primary resonant function and the spurious response suppression function. The acoustically soft materials embedded in the piezoelectric layers provide suppression capability across multiple frequency ranges, allowing a single SCF structure to handle spurious responses from multiple different frequency SCFs simultaneously.
Solution Approach 2:
The acoustically soft materials act as intermediaries between the piezoelectric layers and the spurious resonance modes. These materials with specific impedance values are positioned at antinode locations to mediate and suppress spurious responses, enabling the reflector structure to effectively handle spurious modes from multiple SCF structures operating at different frequencies.
3Reliability
If the thickness of shared electrode is increased to suppress spurious modes, then spurious free range is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the material parameter (acoustic impedance) rather than relying solely on geometric parameter (thickness). By selecting acoustically soft materials with specific impedance values that are lower than the surrounding piezoelectric materials, the patent achieves spurious mode suppression through material property selection, which is more tolerant to thickness variations than precise thickness control.
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 effectively increases the spurious free range of SCFs by shifting mode frequencies and providing a larger frequency spread between modes, improving filter performance and compatibility with advanced mobile communication systems.
Implementation Method 1
a first piezoelectric layer; a second piezoelectric layer
Implementation Method 2
SCF structures are disclosed with increased spurious free ranges by providing various arrangements of acoustically soft materials in one or more locations that correspond with high stress regions of one or more modes
Data Source
AI summary
Acoustic resonators, such as bulk acoustic wave (BAW) resonators and, in particular, acoustic resonators including stacked crystal filters (SCFs) are disclosed. SCF structures are disclosed with increased spurious free ranges by providing various arrangements of acoustically soft materials in one or more locations that correspond with high stress regions of one or more modes. For SCFs operating in first order modes, relative amounts of acoustically soft materials within shared electrodes may be increased. One or more additional layers of acoustically soft materials may also be added to SCF structures near shared electrodes. Accordingly, SCFs may be provided with increased frequency spreads between first order modes and second order modes.