Acoustic Wave Filter Stack for Suppressing Higher-Mode Leakage
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Solution Overview
Problem
Acoustic wave devices with silicon support substrates face issues where higher modes leak to the support substrate side, affecting filter characteristics due to higher acoustic velocities, leading to increased response and interference with main modes.
Innovation Solution
The acoustic wave device incorporates a silicon oxide film on the support substrate, with specific thickness ranges for the silicon oxide film and a piezoelectric body, and includes a high acoustic velocity material layer and dielectric layers to control acoustic velocities and reduce higher mode responses, ensuring the acoustic velocity of the support substrate is lower than or equal to 4700 m/s.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the acoustic velocity of bulk waves in the support substrate is higher than the acoustic velocity of higher modes in the piezoelectric body, then heat radiation properties are improved, but the response of higher modes increases and filter characteristics are adversely influenced
Solution Approach 1:
A silicon oxide film is introduced as an intermediary layer between the piezoelectric body and the silicon support substrate. This mediator layer modifies the acoustic wave propagation by creating a velocity gradient that prevents higher modes from leaking into the support substrate, thereby maintaining filter characteristics while preserving heat radiation properties through the substrate.
Solution Approach 2:
The invention changes the acoustic velocity parameter by controlling the crystal orientation of the silicon support substrate and adjusting the thickness of the silicon oxide film. By setting the acoustic velocity of bulk waves in the support substrate to be equal to or higher than higher mode velocities in the piezoelectric body through parameter optimization, the higher mode response is suppressed while heat radiation is maintained.
2Temperature
If the thickness of the support substrate is increased to improve heat radiation, then heat dissipation is enhanced, but the profile becomes higher and device size increases
Solution Approach 1:
The invention optimizes the thickness parameter of the support substrate within a specific range (3λ to 20λ) to achieve a balance between heat radiation efficiency and profile height. This parameter optimization allows adequate heat dissipation while maintaining a compact device profile suitable for modern electronic systems.
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 the response of higher modes, improving heat radiation properties, energy concentration, and frequency-temperature characteristics while maintaining a low profile and minimizing interference with main modes.
Implementation Method 1
an acoustic wave device in which a piezoelectric body is provided on a support substrate made of silicon
Implementation Method 2
the acoustic velocity of a first higher mode that propagates through the piezoelectric body is equal to an acoustic velocity Vsi of bulk waves that propagate in the support substrate
Data Source
AI summary
An acoustic wave device includes a silicon oxide film, a piezoelectric body, and an interdigital transducer electrode laminated on a support substrate made of silicon. Where a wave length that is determined by an electrode finger pitch of the interdigital transducer electrode is λ, a thickness of the support substrate is greater than or equal to about 3λ. An acoustic velocity of the first higher mode that propagates through the piezoelectric body is an acoustic velocity Vsi=(V1)1/2 of bulk waves that propagate in the support substrate, which is determined by V1 out of solutions V1, V2, and V3 of x derived from the mathematical expression Ax3+Bx2+Cx+D=0, or higher than Vsi.