Lithium Tantalate Acoustic Wave Stack for Out-of-Band Spurious Control
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Solution Overview
Problem
Existing acoustic wave devices with piezoelectric lithium tantalate layers suffer from significant out-of-band spurious responses due to the acoustic velocity characteristics of their components, particularly the interdigital transducer electrodes.
Innovation Solution
The acoustic wave device incorporates a high-acoustic-velocity layer, a lithium tantalate piezoelectric layer, and an interdigital transducer electrode, where the acoustic velocity of bulk waves in the high-acoustic-velocity layer is set to satisfy specific velocity ranges (Vsh0≤Vsub≤Vsp) to confine the SH0 mode within the piezoelectric layer while minimizing spurious responses, using equations and coefficient tables to determine optimal acoustic velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-acoustic-velocity member and low-acoustic-velocity film are used to enclose acoustic waves in the piezoelectric film, then Q characteristics are improved, but out-of-band spurious responses may generate depending on the interdigital transducer electrode properties
Solution Approach 1:
The patent changes the acoustic velocity parameter of the high-acoustic-velocity layer by selecting materials (such as aluminum nitride, silicon carbide, or diamond) and optimizing their thickness to satisfy specific velocity relationships. This parameter optimization allows the device to achieve both high Q characteristics and suppression of spurious responses by ensuring that the acoustic velocity in the high-acoustic-velocity layer is higher than in the piezoelectric layer, while controlling the fast transversal bulk wave velocity to prevent spurious mode generation.
2Reliability
If the acoustic velocity of the high-acoustic-velocity layer is increased to confine acoustic waves, then acoustic wave enclosure is improved, but spurious responses may be generated outside the band
Solution Approach 1:
The patent optimizes the acoustic velocity parameter by selecting appropriate materials and thicknesses for the high-acoustic-velocity layer. The key is to maintain the acoustic velocity higher than the piezoelectric layer for wave confinement, while controlling the fast transversal bulk wave velocity to be within a specific range that prevents spurious responses.
Solution Approach 2:
The patent employs composite material structures combining the high-acoustic-velocity layer with lithium tantalate piezoelectric layers. By selecting materials such as aluminum nitride, silicon carbide, or diamond for the high-acoustic-velocity layer and optimizing their thickness, the device achieves both acoustic wave confinement and suppression of spurious responses through the synergistic effect of the composite structure.
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 significantly reduces out-of-band spurious responses, concentrating acoustic energy in the piezoelectric layer and enhancing the Q value and electrochemical coupling coefficient.
Implementation Method 1
a piezoelectric layer made of lithium tantalate is directly or indirectly laminated on a high-acoustic-velocity layer
Data Source
AI summary
An acoustic wave device includes a high-acoustic-velocity layer, a piezoelectric layer made of lithium tantalate, and an interdigital transducer electrode that are successively laminated. An acoustic velocity of a bulk wave propagating in the high-acoustic-velocity layer is higher than an acoustic velocity of an acoustic wave propagating in the piezoelectric layer, and an acoustic velocity Vsub of a fast transversal bulk wave propagating in the high-acoustic-velocity layer satisfies Vsh0≤Vsub≤Vsp with respect to an acoustic velocity Vsh0 of an SH0 mode and an acoustic velocity Vsp of a mode becoming a spurious of which acoustic velocity is not lower than the acoustic velocity of the SH0 mode, wherein the acoustic velocity Vsh0 and the acoustic velocity Vsp is obtained from Eq. (1).