Acoustic Wave Filter Layout for Bandwidth Tuning Without Q Loss
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Solution Overview
Problem
Existing acoustic wave devices with multilayer substrates face limitations in adjusting fractional band width without deteriorating the Q value, often requiring increased size to ensure capacitance with a thin piezoelectric layer.
Innovation Solution
The acoustic wave device incorporates a substrate with a piezoelectric layer, a high acoustic velocity layer, and a low acoustic velocity layer, featuring an interdigital transducer electrode and a dielectric film with a thickness smaller than the electrode fingers, allowing for adjustable fractional band width without compromising the Q value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Euler angles of the piezoelectric layer are optimized to reduce unwanted waves and prevent Q value deterioration, then the Q value is improved, but the fractional band width is limited to a specific range and becomes less adjustable
Solution Approach 1:
The device segments the functional elements by introducing a first dielectric film as a separate component from the piezoelectric layer. This dielectric film is positioned only in specific regions (between busbar electrodes and/or between electrode fingers) rather than covering the entire piezoelectric layer, allowing independent optimization of Q value (through piezoelectric layer Euler angles) and fractional band width (through dielectric film properties and positioning) without mutual interference.
Solution Approach 2:
The first dielectric film applies local quality modification by being present only in specific regions of the device. It is positioned selectively between busbar electrodes and/or between electrode fingers, creating localized electrical field modifications that adjust fractional band width without affecting the overall piezoelectric layer characteristics that determine Q value. This regional approach allows precise control over capacitance distribution.
2Volume of moving object
If the piezoelectric layer is made thin to reduce device size, then the device size is reduced, but the capacitance decreases requiring increased size to ensure sufficient capacitance
Solution Approach 1:
The first dielectric film acts as an intermediary element that enhances capacitance without requiring increased device size. By positioning this dielectric film with higher permittivity in specific regions (between electrodes), it mediates the electrical field to increase capacitance locally, compensating for the reduced capacitance from the thin piezoelectric layer while maintaining compact dimensions.
Solution Approach 2:
The device employs composite material strategy by combining the piezoelectric layer with a first dielectric film having different material properties (higher permittivity). This composite structure leverages the complementary strengths of each material: the thin piezoelectric layer provides piezoelectric functionality with minimal size, while the dielectric film provides enhanced capacitance through its higher permittivity, achieving both size reduction and sufficient capacitance.
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 small acoustic wave devices and high-frequency filters with adjustable fractional band width while maintaining high Q values, reducing size and improving capacitance per unit area.
Implementation Method 1
a piezoelectric layer on which the IDT electrode is located
Implementation Method 2
a high acoustic velocity layer having a higher acoustic velocity of a bulk wave propagating through the piezoelectric layer than an acoustic velocity of the acoustic wave propagating through the piezoelectric layer, and a low acoustic velocity layer between the piezoelectric layer and the high acoustic velocity layer
Data Source
AI summary
An acoustic wave device includes a substrate, an IDT electrode on the substrate, and a dielectric film on the substrate. The substrate includes a piezoelectric layer, a low acoustic velocity layer, and a high acoustic velocity layer in this order. The IDT electrode includes electrode fingers and busbar electrodes that connect the electrode fingers. On the piezoelectric layer, the dielectric film is located only in a region where the electrode fingers and the busbar electrodes are not located, between the busbar electrodes in a plan view of the substrate. A film thickness of the dielectric film is smaller than a film thickness of the electrode fingers.