Split Ladder Bulk Acoustic Filter With Separate Resonator Stacks
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Solution Overview
Problem
Existing RF filters face challenges in achieving optimal performance parameters such as insertion loss, rejection, isolation, power handling, linearity, size, and cost due to the limitations of using a single material stack for both series and shunt resonators, which affects temperature stability and spurious mode propagation.
Innovation Solution
The implementation of a split ladder filter design, where series and shunt resonators are fabricated on separate chips with distinct material stacks, allowing for separate optimization of each, thereby reducing spurious modes and improving temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single material stack is used for both series and shunt resonators, then device complexity is reduced, but temperature stability and spurious mode suppression deteriorate
Solution Approach 1:
The filter is divided into two separate modules: a first module containing series resonators with a first material stack, and a second module containing shunt resonators with a second material stack. This segmentation allows each module to be optimized independently for its specific functional requirements, resolving the contradiction between device complexity and temperature stability.
Solution Approach 2:
Different material stacks are assigned to different parts of the filter based on their specific needs. The first material stack is optimized for series resonators while the second material stack is optimized for shunt resonators, allowing each region to have the quality characteristics needed for its function, thereby improving overall temperature stability without excessive complexity.
2Ease of manufacture
If a single material stack is used for both series and shunt resonators, then manufacturing process is simplified, but spurious mode propagation increases
Solution Approach 1:
The filter structure is segmented into separate modules for series and shunt resonators, each with dedicated material stacks. This segmentation prevents spurious modes generated in one module from propagating to the other, as the modules are electrically isolated by the series resonators, thus reducing harmful spurious modes while maintaining manufacturing feasibility.
Solution Approach 2:
The series resonators act as intermediary elements that electrically isolate the first module from the second module. This isolation prevents spurious modes generated in the shunt resonator module from propagating through the series resonators, effectively suppressing harmful spurious modes while allowing separate optimization of material stacks.
3Reliability
If separate material stacks are used for series and shunt resonators, then temperature stability improves, but device complexity increases
Solution Approach 1:
The filter is segmented into functionally independent modules, each with its own optimized material stack. This segmentation achieves temperature stability through independent optimization while managing complexity through modular architecture, where each module can be designed and manufactured separately.
Solution Approach 2:
The solution moves from a single-plane material stack configuration to a multi-dimensional modular architecture. By distributing different material stacks across separate modules rather than attempting to optimize a single unified stack, the patent achieves temperature stability while organizing complexity in a manageable spatial and functional dimension.
4Object-generated harmful factors
If separate material stacks are used for series and shunt resonators, then spurious modes are reduced, but manufacturing complexity increases
Solution Approach 1:
The filter is manufactured as separate modules that can be independently fabricated and then assembled. This segmentation allows each module to be optimized for its specific resonator type while simplifying the overall manufacturing process through modular assembly, reducing the complexity of handling multiple material stacks in a single monolithic structure.
Solution Approach 2:
The patent transitions from a single-layer manufacturing approach to a multi-layer modular assembly approach. Different material stacks are fabricated in separate modules and then combined in a higher-dimensional assembly process, which simplifies the fabrication of each individual module while achieving the overall complex configuration needed to suppress spurious modes.
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 split ladder filter design achieves improved insertion loss, temperature stability, and reduced spurious modes, enhancing overall filter performance and cost-effectiveness by optimizing material stacks for series and shunt resonators separately.
Implementation Method 1
The first acoustic wave resonator includes a first stack comprising a first piezoelectric material... The second acoustic wave resonator includes a second stack comprising a second piezoelectric material
Implementation Method 2
solidly-mounted transversely-excited bulk acoustic resonator... acoustic wave resonators
Data Source
AI summary
A filter device is provided that includes a first chip comprising a first IDT of a first solidly-mounted resonator on a surface of a first piezoelectric layer. The IDT including a first plurality of interleaved fingers having a first thickness. A first acoustic reflector is sandwiched between the first piezoelectric layer and a first base. The filter device includes a second chip having a second IDT of a second solidly-mounted resonator on a surface of a second piezoelectric layer. The second IDT includes a second plurality of interleaved fingers having a second thickness that is different from the first thickness. A second acoustic reflector is sandwiched between the second piezoelectric layer and a second base. An electrical connection is provided between the first IDT and the second IDT.