Shared-Die BAW Filter Layout for Compact RF Multiplexers
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Solution Overview
Problem
The increasing demand for compact, low-loss, and low-temperature-drift radio frequency (RF) filters in mobile communication systems poses challenges in achieving desirable filter performance while reducing size and cost, particularly for bulk acoustic wave (BAW) filters, which typically occupy a single die and have limited material thickness variations.
Innovation Solution
The solution involves co-packaging multiple BAW filters on a single die, sharing a common material stack and trimming steps to achieve different resonant frequencies, allowing for flexible and complex designs while reducing mask costs and fabrication time, and enabling the use of shared processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple BAW filters are packaged on separate dies, then each filter can be independently manufactured with optimized performance, but the overall packaging size and fabrication cost increase
Solution Approach 1:
The patent combines multiple BAW filters onto a single die by sharing a common material stack (piezoelectric layer, electrodes, and acoustic reflectors) among multiple filter structures. This merging approach reduces the overall packaging size while maintaining independent filter performance through shared fabrication processes and common acoustic isolation structures.
Solution Approach 2:
The common material stack serves multiple functions simultaneously: it provides the piezoelectric active layer for all filters, acts as an acoustic reflector for multiple resonators, and enables shared trimming processes. This multi-functionality allows different filters to operate at different frequencies while sharing the same physical infrastructure on the die.
2Reliability
If multiple BAW filters are packaged on separate dies, then each filter can be independently optimized, but fabrication time and mask costs increase
Solution Approach 1:
The patent merges multiple filter fabrication processes into a single unified process by forming all piezoelectric layers, electrodes, and acoustic reflectors in shared fabrication steps. This approach reduces the total number of deposition and etching cycles required, thereby decreasing fabrication time and mask costs while maintaining filter performance.
Solution Approach 2:
The common material stack is formed in advance before the filters are individually defined and trimmed. By preparing the shared piezoelectric layer and electrode structures first, subsequent filter-specific processing can be performed more efficiently with fewer additional fabrication steps.
3Ease of manufacture
If BAW filters use fixed material thickness, then manufacturing is simplified, but resonant frequency flexibility is limited
Solution Approach 1:
The patent applies local quality by maintaining a common material stack thickness for all filters while introducing local variations through selective trimming of piezoelectric layer portions or electrode structures. This allows each filter to achieve its specific resonant frequency requirement without changing the overall manufacturing process, combining manufacturing simplicity with frequency flexibility.
Solution Approach 2:
The patent changes physical parameters (such as piezoelectric layer thickness or electrode dimensions) through selective trimming processes after the common material stack is formed. This enables resonant frequency adjustment for individual filters while maintaining the same base material stack, providing frequency versatility without complicating the primary manufacturing process.
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 reduces the overall size of the filter packaging, decreases fabrication time and costs, and allows for more flexible design options by utilizing shared trimming steps and material stacks, enhancing the performance and efficiency of BAW filters in RF systems.
Implementation Method 1
acoustic waves propagate in a bulk of a piezoelectric layer
Implementation Method 2
In BAW filters, acoustic waves propagate in a bulk of a piezoelectric layer
Data Source
AI summary
Bulk acoustic wave resonators of two or more different filters can be on a common die. The two filters can be included in a multiplexer, such as a duplexer, or implemented as standalone filters. With bulk acoustic wave resonators of two or more filters on the same die, the filters can be implemented in less physical space compared to implementing the same filters of different die. Related methods, radio frequency systems, radio frequency modules, and wireless communication devices are also disclosed.