Two-Stage LBAW Filter Layout for Parasitic Sideband Suppression
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Solution Overview
Problem
Existing radio-frequency acoustic wave filters, particularly Lateral Bulk Acoustic Wave (LBAW) filters, suffer from unwanted sidebands that degrade their band pass filter characteristics, limiting their performance and efficiency.
Innovation Solution
The solution involves cascading multiple LBAW filters with different thickness and electrode configurations to suppress parasitic sidebands by adjusting the resonance frequencies of the second-order acoustic thickness-shear mode, thereby improving the band pass response and simplifying the fabrication process.
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 sections (first LBAW filter and second LBAW filter) that are coupled together. Each section has different piezoelectric layer thicknesses to create different resonance frequencies, allowing the combined structure to suppress sidebands while maintaining individual section simplicity.
Solution Approach 2:
Different regions of the filter structure have different piezoelectric layer thicknesses (first thickness in the first LBAW filter, second thickness in the second LBAW filter). This local variation in quality creates different resonance characteristics in different parts of the filter, enabling sideband suppression through constructive and destructive interference patterns.
2Reliability
If multiple LBAW filters with different thicknesses are cascaded, then sidebands are suppressed and band pass response improves, but device complexity increases
Solution Approach 1:
Multiple LBAW filter sections are merged into a single integrated device structure. The first and second LBAW filters share common electrodes and are formed on the same substrate, combining their functions into one unified component that achieves sideband suppression without requiring separate discrete devices.
Solution Approach 2:
The intermediate electrode serves multiple functions: it acts as the output electrode for the first LBAW filter, the input electrode for the second LBAW filter, and provides electrical connection between the two sections. This multi-functionality reduces the total number of components needed.
3Productivity
If LBAW filters operate at higher frequencies with wider bandwidths, then productivity and performance improve, but parasitic sidebands become more problematic
Solution Approach 1:
The filter utilizes mechanical resonance of the piezoelectric layers at specific frequencies. By designing the thicknesses to create different resonance frequencies in the first and second LBAW filters, the system exploits constructive interference in the passband and destructive interference in the sidebands, effectively suppressing parasitic vibrations at unwanted frequencies.
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 sidebands, enhancing the band pass response of LBAW filters, allowing them to operate at higher frequencies with wider bandwidths and smaller sizes, while maintaining the simplicity of using a single piezoelectric layer.
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
The first multilayer stack and second multilayer stack are configured such that application of a radio frequency voltage creates acoustic modes in the piezoelectric layer, including acoustic thickness-extensional resonance modes
Implementation Method 3
The intermediary layer has a first region and a second region, the first region having a first layer thickness and the second region having a second layer thickness different from the first layer thickness
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.