Acoustic Wave Substrate Orientation for Wideband Higher-Order Mode Control
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Solution Overview
Problem
Existing acoustic wave devices struggle to sufficiently suppress spurious higher-order modes in a wide band.
Innovation Solution
The acoustic wave device incorporates a support substrate with a first and second silicon layer, each having specific plane orientations and angles relative to the piezoelectric film, and uses lithium tantalate or lithium niobate film with a thickness of about 1λ or less, to reduce or prevent higher-order modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer silicon support substrate is used, then the device structure is simple, but higher-order modes cannot be sufficiently suppressed in a wide band
Solution Approach 1:
The support substrate is segmented into multiple silicon layers (first silicon layer and second silicon layer) with different plane orientations. This segmentation allows each layer to contribute differently to acoustic wave propagation, enabling suppression of higher-order modes while maintaining overall structural simplicity.
Solution Approach 2:
Different regions of the support substrate (different silicon layers) are given different local qualities through varying their plane orientations. The first silicon layer has one orientation while the second silicon layer has another, creating local variations that selectively suppress higher-order modes without affecting the fundamental mode uniformly.
2Power
If the piezoelectric film thickness is increased, then the acoustic wave generation is enhanced, but higher-order modes are more difficult to suppress
Solution Approach 1:
The thickness of the piezoelectric film is optimized to be 1λ or less (where λ is the wavelength defined by electrode finger pitch). This parameter change ensures that the film is thin enough to suppress higher-order modes while still being thick enough to generate sufficient acoustic wave power for device operation.
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 effectively reduces or prevents higher-order modes across a wide band, enhancing the Q factor and frequency-temperature characteristics of the acoustic wave device.
Implementation Method 1
a piezoelectric film directly or indirectly on the support substrate, and an IDT electrode on the piezoelectric film
Data Source
AI summary
An acoustic wave device includes a support substrate, a piezoelectric film, and an IDT electrode. When a wavelength defined by an electrode finger pitch of the IDT electrode is λ, a thickness of the piezoelectric film is about 1λ or less. The piezoelectric film has crystal axes. The support substrate includes first and second silicon layers. A plane orientation of the first and second silicon layers is (100), (110), or (111). When angles α1 and β2 are defined between the plane orientations of the first and second silicon layers and the crystal axes, each of the angles α1 and α2 is one of three types of angles of an angle α100, an angle α110, and an angle α111. A type of the angle α1 is different from a type of the angle α2 and/or a value of the angle α1 is different from a value of the angle α2.