Acoustic Wave Resonator Structure for Higher Capacitance Density
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Solution Overview
Problem
Acoustic wave devices using bulk waves in the thickness-shear mode face challenges in increasing capacitance while reducing size due to increased electrode finger pitch and decreased duty cycle, making it difficult to achieve desired performance.
Innovation Solution
The acoustic wave device incorporates a piezoelectric layer made of lithium niobate or lithium tantalate with an interdigital transducer electrode and a dielectric film, where the electrode finger pitch is optimized such that p/d ≥ about 4.25, allowing for increased capacitance and size reduction without increasing the electrode finger pitch, and the thickness of the dielectric film is adjusted to facilitate frequency adjustment without enlarging the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If bulk waves in thickness-shear mode are used, then acoustic wave propagation is enabled, but electrode finger pitch increases and duty cycle decreases
Solution Approach 1:
The patent changes the physical parameters of the piezoelectric layer by introducing a cavity to reduce its effective thickness. This allows the use of thinner piezoelectric layers while maintaining the desired acoustic wave propagation characteristics, thereby enabling smaller electrode finger pitch and higher duty cycle
2Ease of manufacture
If electrode finger pitch is increased, then acoustic wave device can be fabricated, but capacitance cannot be increased
Solution Approach 1:
The patent introduces a cavity in the piezoelectric layer to effectively reduce the thickness parameter, which enables the achievement of desired capacitance values with smaller electrode finger pitch and higher duty cycle, thus increasing capacitance without compromising fabrication ease
3Quantity of substance
If capacitance is increased, then desired performance is achieved, but device size increases
Solution Approach 1:
By introducing a cavity to reduce the effective piezoelectric layer thickness, the patent enables achieving desired capacitance values with reduced device dimensions. The cavity allows for higher duty cycle and smaller electrode pitch, which increases capacitance density and reduces overall device size
Solution Approach 2:
The cavity structure effectively nests within the piezoelectric layer, creating a compact structure that increases the electric field concentration and capacitance density without increasing the external device dimensions
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 enhances capacitance, reduces device size, and improves fractional band width and ripple reduction, enabling more efficient acoustic wave propagation and filter performance.
Implementation Method 1
an acoustic wave device using bulk waves in a thickness-shear mode... Bulk waves in the thickness-shear mode are excited by applying an alternating-current voltage between the electrodes
Data Source
AI summary
An acoustic wave device includes a support including a cavity, a piezoelectric layer on or above the support and made of one of lithium niobate or lithium tantalate, an interdigital transducer electrode embedded in the piezoelectric layer and including surfaces opposed to each other in a thickness direction, one of the surfaces being in contact with the piezoelectric layer, and a dielectric film on the piezoelectric layer and covering the interdigital transducer electrode. The interdigital transducer electrode includes electrode fingers, at least one of which overlaps the cavity in plan view. Assuming a thickness of the piezoelectric layer is d and an electrode finger pitch of the interdigital transducer electrode is p, p/d≥ about 4.25.