Acoustic Wave Layer Stack for Fractional Bandwidth Control
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Solution Overview
Problem
Existing acoustic wave devices face difficulties in adjusting the fractional bandwidth to achieve steep filter characteristics, making it challenging to efficiently modify their bandpass filter properties.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer with an IDT electrode and a conductive material layer, where the thickness of the dielectric layer is optimized to satisfy a specific formula, and the conductive material layer is strategically positioned to overlap with the IDT electrode, allowing for efficient adjustment of the fractional bandwidth through capacitive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-resistance layer is provided on the support substrate with piezoelectric layer and IDT electrode stacked on it, then spurious responses are suppressed, but the fractional bandwidth cannot be adjusted efficiently
Solution Approach 1:
The conductive material layer is divided into multiple independent conductive regions positioned at specific locations below the IDT electrode fingers. This segmentation allows each region to independently contribute to capacitance control, enabling precise adjustment of fractional bandwidth while maintaining spurious response suppression through the overall low-resistance layer structure.
Solution Approach 2:
Different regions of the conductive material layer are positioned at different locations below the IDT electrode, with each region having specific area and positioning characteristics. This local quality variation allows differential control of capacitance in different areas, achieving fractional bandwidth adjustment while maintaining overall signal integrity and spurious response suppression.
2Adaptability or versatility
If the conductive material layer area is increased to adjust fractional bandwidth, then bandwidth reduction is achieved, but device area increases
Solution Approach 1:
Instead of increasing the conductive material layer area in the planar direction to adjust fractional bandwidth, the invention positions multiple conductive regions at different vertical depths and horizontal locations below the IDT electrode. This three-dimensional arrangement allows capacitance control without proportionally increasing the device footprint, achieving bandwidth adjustment with minimal area penalty.
Solution Approach 2:
The multiple conductive regions are nested within the vertical structure below the IDT electrode, with each conductive region positioned at different depths and locations. This nested arrangement maximizes the use of vertical space rather than horizontal space, allowing fractional bandwidth adjustment while keeping the device area compact.
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 configuration enables efficient adjustment of the fractional bandwidth, reducing it to a desired level while maintaining effective excitation of the desired mode, thereby improving the filter characteristics and allowing for miniaturization of the device.
Implementation Method 1
a piezoelectric layer including a first main surface and a second main surface opposing each other, an Interdigital Transducer (IDT) electrode on the first main surface of the piezoelectric layer
Implementation Method 2
a conductive material layer on a surface of the dielectric layer on a side opposite to the piezoelectric layer. The conductive material layer is provided in at least a portion of a region overlapping the IDT electrode in a plan view
Data Source
AI summary
An acoustic wave device includes an Interdigital Transducer (IDT) electrode on a first main surface of a piezoelectric layer, a conductive material layer on a second main surface of the piezoelectric layer, and a dielectric layer provided between the piezoelectric layer and the conductive material layer. When a film thickness of the piezoelectric layer is represented as Tp[λ] and a film thickness of the dielectric layer is represented as Td[λ], the Formula (1) is satisfied or Td=0, where λ is a wavelength determined by an electrode finger pitch of the IDT electrode, and Tp[λ]≥about 0.025:Td[λ]≤−2.369×(Tp[λ])4 +2.721×(Tp[λ])3 −1.049×(Tp[λ])2 +0.076×(Tp[λ])+0.095 Formula (1).