Composite Acoustic Substrate Structure for Spurious Mode Suppression
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Solution Overview
Problem
Acoustic wave devices with composite substrates of silicon and piezoelectric layers often experience spurious responses due to high-order modes, particularly at higher frequency sides, which affect their performance.
Innovation Solution
A composite substrate is designed with a silicon support substrate, a lithium tantalate piezoelectric layer, and strategically placed high and low acoustic velocity films, along with specific Euler angles for the silicon substrate to reduce or prevent spurious responses by controlling the propagation of bulk waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a composite substrate with silicon support substrate and piezoelectric layer is used, then the acoustic wave device achieves good frequency characteristics, but spurious responses occur due to high-order modes at higher frequency sides
Solution Approach 1:
A buffer layer is introduced between the piezoelectric layer and the silicon support substrate to control the propagation of bulk waves. This intermediary layer prevents harmful high-order modes from generating spurious responses while maintaining the beneficial frequency characteristics of the composite substrate structure.
Solution Approach 2:
The acoustic velocity of the buffer layer is specifically designed to be lower than that of the piezoelectric layer. This parameter change in acoustic velocity creates conditions that suppress bulk wave propagation and high-order mode generation, thereby eliminating spurious responses at higher frequencies.
2Object-generated harmful factors
If the acoustic velocity of the buffer layer is made lower than the piezoelectric layer, then spurious responses are reduced, but the device complexity increases due to additional layer requirements
Solution Approach 1:
The buffer layer is positioned specifically at the interface between the piezoelectric layer and silicon substrate where bulk wave generation occurs. By applying the acoustic velocity control principle only at this critical location rather than throughout the entire device, the solution addresses spurious responses with minimal additional complexity.
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
The solution effectively reduces or eliminates spurious responses from high-order modes, improving the frequency characteristics and reducing unwanted phase shifts in acoustic wave devices.
Implementation Method 1
an acoustic velocity of a bulk wave propagating is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer
Implementation Method 2
an acoustic velocity of a bulk wave propagating is lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer
Implementation Method 3
a piezoelectric layer made of lithium tantalate laminated on the support substrate
Data Source
AI summary
A composite substrate includes a support substrate made of Si, a high acoustic velocity material layer, a low acoustic velocity film, and a piezoelectric layer. In Euler angles (φ, θ, ψ) of the Si, φ and θ are within regions indicated by hatching with slant lines in FIG. 4. An acoustic wave device includes an IDT electrode in contact with the piezoelectric layer of the composite substrate.