Two-Stage LBAW Filter Layout for RF Sideband Suppression

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Solution Overview

Problem

Lateral Bulk Acoustic Wave (LBAW) filters used in radio-frequency applications suffer from unwanted sidebands, which degrade their band pass filter characteristics, and existing solutions are complex and not optimized for high-frequency operation.

Innovation Solution

The implementation of cascaded LBAW filters with different thickness and electrode configurations to suppress sidebands, where the second layer thickness is greater than the first, and the electrodes are designed to create distinct resonance frequencies, allowing for improved band pass response and simplified fabrication.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If LBAW filters are used in radio-frequency applications, then small size and mass-production capability are achieved, but unwanted sidebands are generated that degrade band pass filter characteristics

Engineering Contradiction:

Improvefilter sizeVSAvoidsidebands

Core Design Contradiction:

Volume of moving objectVSObject-generated harmful factors

Solution Approach 1:

The filter is divided into multiple cascaded LBAW resonators with different thicknesses. Each resonator segment handles specific frequency components, with the first resonator passing the main signal and subsequent resonators filtering out sidebands at different frequencies, thereby eliminating harmful sidebands while maintaining compact size

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the piezoelectric layer have different thicknesses to create distinct resonance frequencies. The first LBAW resonator has a specific thickness for the main passband, while subsequent resonators have different thicknesses tailored to suppress specific sideband frequencies, allowing localized optimization of filter characteristics

Inventive Principle:

Principle #3Local quality

2Object-generated harmful factors

If conventional filter designs are used to suppress sidebands, then band pass characteristics are improved, but device complexity increases

Engineering Contradiction:

Improvesideband suppressionVSAvoidfilter structure

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

Multiple LBAW resonators are merged into a single integrated filter structure by cascading them together. The resonators share common electrodes and piezoelectric layer regions, allowing sideband suppression functionality to be combined with the main filtering operation in a unified compact device rather than separate complex components

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The cascaded LBAW resonator structure serves multiple functions simultaneously: the first resonator provides the main band pass filtering, while subsequent resonators with different thicknesses provide sideband suppression at multiple frequency points, and the entire structure maintains compact size suitable for RF applications

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Speed

If LBAW filters operate at higher frequencies, then bandwidth is increased, but fabrication precision requirements become more stringent

Engineering Contradiction:

Improveoperating frequencyVSAvoidlayer thickness control

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The filter operates at higher frequencies by changing the thickness parameter of the piezoelectric layer. By precisely controlling the layer thickness during fabrication, the resonant frequency is tuned to achieve wider bandwidth operation while the standardized fabrication process maintains manufacturing feasibility

Inventive Principle:

Principle #35Parameter changes

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, enhances the band pass response, and allows LBAW filters to operate at higher frequencies with wider bandwidths, while simplifying the fabrication process and reducing size 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

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

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

Methodology Applied

Scientific EffectAcoustic resonance: Resonance

Data Source

PatentUS10630256B2Two-stage lateral bulk acoustic wave filter

Publication Date: 2020.04.21 TEKNOLOGIAN TUTKIMUSKESKUS VTT OY

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.