Two-Stage LBAW Filter Structure for TS2 Sideband Suppression
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Solution Overview
Problem
Existing radio-frequency (RF) band pass filters based on Lateral Bulk Acoustic Wave (LBAW) technology suffer from unwanted sidebands, which affect their band pass filter characteristics and performance.
Innovation Solution
The solution involves cascading multiple LBAW filters with different thickness and electrode configurations to suppress sidebands by adjusting the resonance frequencies of the second-order acoustic thickness-shear (TS2) mode, allowing the first-order thickness-extensional (TE1) mode to maintain its characteristics while reducing the impact of TS2 mode sidebands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single LBAW filter is used, then the device complexity is low, but parasitic sidebands appear that degrade filter performance
Solution Approach 1:
The filter is divided into multiple LBAW filter stages (first LBAW filter and second LBAW filter) connected in series. Each stage has its own piezoelectric layer, electrodes, and acoustic reflector structure. This segmentation allows each stage to contribute to suppressing parasitic sidebands at different frequencies, improving overall filter performance while eliminating the sidebands that would appear in a single-stage design.
2Reliability
If multiple LBAW filters are cascaded to suppress sidebands, then filter performance improves, but device complexity increases
Solution Approach 1:
The first and second LBAW filters are designed with different local characteristics: the first LBAW filter has a first piezoelectric layer thickness optimized for suppressing sidebands at a first frequency, while the second LBAW filter has a second piezoelectric layer thickness optimized for suppressing sidebands at a second frequency. This local differentiation allows each stage to target specific parasitic frequencies, improving overall performance without requiring all components to be uniformly complex.
Solution Approach 2:
The patent employs parameter changes by varying the piezoelectric layer thickness between the first and second LBAW filters. The first piezoelectric layer has a thickness that creates acoustic resonance at a frequency that suppresses sidebands at a first frequency, while the second piezoelectric layer has a different thickness that creates resonance at a frequency that suppresses sidebands at a second frequency. This parameter variation enables effective sideband suppression across multiple frequency ranges.
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 suppresses parasitic sidebands, improving the band pass response of LBAW filters and allowing them to operate at higher frequencies with wider bandwidths and simpler fabrication compared to conventional filters.
Implementation Method 1
By applying an alternating voltage across the piezoelectric layer at the input resonator, a mechanical resonance is formed in the piezoelectric layer below the input electrode
Implementation Method 2
application of a radio frequency voltage between the first input electrode and the first counter electrode layer creates acoustic modes in the piezoelectric layer between the first input and output electrodes and between the second input and output electrodes
Data Source
AI summary
Acoustic wave filter devices are disclosed. A device includes a layer providing or on a topmost layer of an acoustic reflector. The intermediary layer has a first region and a second region. The first region has a first layer thickness and the second region has a second layer thickness different from the first layer thickness. The device includes a first multilayer stack on the first region and a second multilayer stack on the second region of the intermediary layer. Each of the first and the second stacks includes a piezoelectric layer on a counter electrode that is located on the respective region, an input and an output electrode. Application of a radio frequency voltage between the input electrode and the counter electrode layer of the first stack creates acoustic resonance modes in the piezoelectric layer between the input and output electrodes of the first and the second stack.