Split Ladder Bulk Acoustic Filter With Separate Series and Shunt Chips
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Solution Overview
Problem
Conventional RF filters using acoustic wave resonators face challenges in achieving optimal performance across different frequency bands due to the need for a single material stack that meets the distinct requirements of series and shunt resonators, leading to suboptimal design trade-offs in insertion loss, temperature stability, and power handling.
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 independent optimization of each resonator type to improve frequency selectivity and temperature stability, thereby enhancing the filter's performance across the desired frequency range.
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 performance optimization is limited due to conflicting requirements
Solution Approach 1:
The filter is divided into two separate modules: series resonators and shunt resonators, each with its own optimized material stack. This segmentation allows independent optimization of material properties for each resonator type, resolving the conflict between device complexity and performance reliability.
2Manufacturing precision
If different material stacks are used for series and shunt resonators, then frequency selectivity and temperature stability are improved, but manufacturing complexity increases
Solution Approach 1:
The filter structure is segmented into separate series and shunt resonator modules that can be manufactured independently with different material stacks, then assembled together. This approach enables precise frequency control while managing manufacturing complexity through modular construction.
Solution Approach 2:
Different material stacks are applied locally to different resonator types based on their specific performance requirements. Series resonators use materials optimized for their electrical characteristics, while shunt resonators use materials optimized for their function, achieving local quality optimization throughout the filter structure.
3Stability of the object's composition
If bonded-wafer series resonators are used, then temperature stability is improved, but cost increases compared to non-bonded designs
Solution Approach 1:
Bonded-wafer construction is applied specifically to series resonators where temperature stability is critical for maintaining electrical characteristics, while non-bonded designs are used for shunt resonators where cost is more important. This localized application of bonding technology optimizes the temperature-cost tradeoff.
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 enables better frequency selectivity and reduced temperature sensitivity, meeting specific insertion loss requirements and improving the overall performance of RF filters, as demonstrated in the LTE Band 2 transmit filter example, while also offering cost benefits by using bonded-wafer series resonators and non-bonded SAW shunt resonators.
Implementation Method 1
The resonator includes a piezoelectric material sandwiched between a first electrode and a second electrode
Implementation Method 2
acoustic wave resonators... Solidly-mounted transversely-excited film bulk acoustic resonator
Data Source
AI summary
Filter devices. A first chip includes a first base, a first piezoelectric membrane having a first thickness, and a first acoustic Bragg reflector sandwiched between the first piezoelectric membrane and the first base. A first interdigital transducer (IDT) of a first solidly-mounted membrane resonator is formed on a surface of the first piezoelectric membrane. A second chip includes a second base, a second piezoelectric membrane having a second thickness less than the first thickness, and a second acoustic Bragg reflector sandwiched between the second piezoelectric membrane and the second base. A second IDT of a second solidly-mounted membrane resonator is formed on a surface of the second piezoelectric membrane. A circuit card is coupled to the first chip and the second chip, the circuit card including at least one conductor for making an electrical connection between the first IDT and the second IDT.