BAW Filter Rejection-Band Resonators for High-Frequency Quality
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Solution Overview
Problem
Current bulk acoustic wave resonators using polycrystalline piezoelectric thin films face degradation in quality at frequencies above 5 GHz due to thickness limitations, while single crystalline films maintain performance but are challenging to manufacture and transfer effectively.
Innovation Solution
The development of bulk acoustic wave resonator filters incorporating single crystalline or epitaxial piezoelectric thin films with advanced transfer processes and structures, such as sacrificial layers and multilayer mirrors, to enhance quality factor and electro-mechanical coupling for high-frequency applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polycrystalline piezoelectric thin films are used in bulk acoustic wave resonators, then manufacturing is easier and cost is lower, but quality degrades at frequencies above 5 GHz due to thickness limitations
Solution Approach 1:
The patent uses sacrificial layers (sacrificial membrane, sacrificial oxide layer, sacrificial nitride layer) that are intentionally designed to be temporary and removable. These sacrificial structures enable the transfer and release of single crystalline piezoelectric thin films onto the resonator structure, then are discarded after serving their purpose. This approach makes the complex single crystalline film manufacturing process more feasible by breaking it into manageable steps with removable intermediates.
Solution Approach 2:
The patent employs multiple intermediary layers including sacrificial membranes, sacrificial oxide layers, and sacrificial nitride layers that facilitate the transfer process. These intermediary structures mediate between the single crystalline piezoelectric film and the final resonator structure, enabling controlled release and positioning while maintaining film integrity during the manufacturing process.
2Reliability
If single crystalline piezoelectric thin films are used to maintain performance at high frequencies, then quality factor and electro-mechanical coupling improve, but manufacturing and transfer become challenging
Solution Approach 1:
The patent segments the manufacturing process into distinct stages using separate sacrificial layers for different functions: sacrificial membrane for initial release, sacrificial oxide layer for intermediate handling, and sacrificial nitride layer for final transfer. This segmentation allows each step to be optimized independently, making the overall complex process of manufacturing single crystalline film resonators more manageable and reproducible.
Solution Approach 2:
The patent performs preliminary actions by pre-forming the sacrificial layer structure and single crystalline piezoelectric thin film on a substrate before the actual resonator assembly. The sacrificial layers are prepared in advance with specific thicknesses and material properties to enable controlled release at later stages, facilitating the transfer of pre-grown single crystalline films onto the resonator structure without damage.
3Speed
If piezoelectric thin film thickness is reduced to achieve higher frequency operation, then resonant frequency increases, but quality degrades in polycrystalline films
Solution Approach 1:
The patent changes the material parameter from polycrystalline to single crystalline structure, which fundamentally alters the film's properties. Single crystalline piezoelectric thin films maintain their piezoelectric coefficients and structural integrity at reduced thicknesses, enabling high-frequency operation (above 5 GHz) without the quality degradation that plagues polycrystalline films of similar 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
These filters achieve improved performance and cost-efficiency by maintaining high piezoelectric quality even at thin thicknesses, addressing the limitations of polycrystalline films and facilitating the use of single crystalline films in high-frequency BAWR applications.
Implementation Method 1
bulk acoustic wave resonators using polycrystalline piezoelectric thin films
Implementation Method 2
Bulk acoustic wave resonator filters including rejection-band resonators
Data Source
AI summary
A BAW resonator filter can include a BAW resonator pass-band filter ladder, the BAW resonator pass-band filter ladder can be configured to pass frequency components of an input signal in a pass-band of frequencies received at an input node of the BAW resonator pass-band filter ladder to an output node of the BAW resonator pass-band filter ladder. A first rejection-band series resonator can be coupled in series between an input port of the BAW resonator pass-band filter ladder and the input node, the first rejection-band series resonator can have a first anti-resonant frequency peak in a rejection-band of frequencies that is less than the pass-band of frequencies. A second rejection-band series resonator can be coupled in series between an output port of the BAW resonator filter and the output node, the second rejection-band series resonator can have a second anti-resonant frequency peak in the rejection-band of frequencies.