Acoustic Wave Resonator Structure for Spurious Emission Reduction
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Solution Overview
Problem
Existing acoustic wave devices face challenges in reducing spurious emissions while minimizing device size, particularly in piezoelectric thin film resonators used in high-frequency circuits.
Innovation Solution
The acoustic wave device incorporates a substrate with a lower and upper electrode, a piezoelectric film sandwiched between them, featuring through holes along the resonance region and additional films in edge regions, connected to an air gap, which excite thickness-shear vibration and surround the resonance region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If additional films are formed in the edge region within the resonance region to reduce spurious emissions, then spurious emissions are reduced, but the device size increases
Solution Approach 1:
The patent extracts the spurious emission reduction function from the traditional edge region additional films and relocates it to irregularities on the reflecting surfaces. By removing the additional films from the edge region and replacing them with surface irregularities, the device achieves spurious emission reduction without the area penalty of extended film structures
Solution Approach 2:
The patent replaces the mechanical/structural approach of adding films with a surface topology approach using irregularities. Instead of adding material layers to control acoustic waves, the invention uses controlled surface roughness or geometric irregularities on the reflecting surfaces to achieve the same acoustic wave control with reduced device footprint
2Object-generated harmful factors
If through holes are provided along the resonance region to manage acoustic wave propagation, then spurious emissions are reduced, but manufacturing complexity increases
Solution Approach 1:
The patent merges the through holes with the additional films by forming the through holes through the additional films. This integration allows the acoustic wave management function to be achieved through the combined structure, where the through holes provide direct acoustic paths while the additional films provide reflective surfaces, accomplishing spurious emission reduction without requiring separate manufacturing processes for each component
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 reduces spurious emissions and miniaturizes the device by effectively utilizing through holes and additional films to manage acoustic wave propagation, thereby enhancing performance and reducing size.
Implementation Method 1
a piezoelectric film that is provided over the substrate, at least a part of the piezoelectric film being interposed between the lower electrode and the upper electrode... The lower electrode and the upper electrode may excite thickness-shear vibration in the piezoelectric film
Implementation Method 2
an air gap, the air gap being formed between the substrate and the lower electrode and overlapping with the resonance region in the plan view... acoustic wave is reflected at the periphery of the resonance region
Data Source
AI summary
An acoustic wave device includes a substrate, lower and upper electrodes provided over the substrate, a piezoelectric film that is provided over the substrate, is interposed between the lower and upper electrodes, and has a pair of through holes that sandwich a resonance region therebetween in a first direction, are provided along the resonance region, and are connected to an air gap that is formed between the substrate and the lower electrode and overlaps the resonance region in the plan view, the lower and upper electrodes overlapping across the piezoelectric film in the resonance region, and additional films that are not provided in a central region of the resonance region in the plan view and are provided in respective edge regions, which are located on respective sides of the central region in a second direction substantially orthogonal to the first direction in the plan view, of the resonance region.