Acoustic Wave Resonator Layout for Ripple and Stop Band Control
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Solution Overview
Problem
Acoustic wave devices with inclined IDT electrodes effectively suppress transverse mode ripple but often experience deteriorated filter characteristics due to increased response at the upper end of the stop band, particularly in multilayer bodies with high acoustic wave energy confinement.
Innovation Solution
The acoustic wave device incorporates a piezoelectric body layer with a high acoustic velocity member and IDT electrodes, where series arm resonators use inclined IDT electrodes and parallel arm resonators employ the piston mode, featuring interdigitating electrode fingers with specific velocity regions to reduce both transverse mode ripple and stop band response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an inclined IDT electrode is used to suppress transverse mode ripple, then transverse mode ripple is reduced, but the response at the upper end of the stop band becomes large
Solution Approach 1:
The patent applies local quality by creating regions with different acoustic velocities within the multilayer body. Specifically, it introduces a low acoustic velocity film between the piezoelectric body layer and the inclined IDT electrode, and a high acoustic velocity film on the opposite side of the piezoelectric body layer. This local variation in acoustic velocity properties allows different regions to perform different functions: the low acoustic velocity region suppresses transverse mode ripple while the high acoustic velocity region controls the stop band response.
Solution Approach 2:
The patent uses composite materials by combining multiple layers with different acoustic velocity characteristics. The multilayer body consists of a piezoelectric body layer, a low acoustic velocity film, and a high acoustic velocity film, creating a composite structure that leverages the complementary properties of each material to simultaneously address both harmful effects.
2Reliability
If a multilayer body with high acoustic wave energy confinement is used, then Quality factor is increased, but the response at the upper end of the stop band becomes more prominent
Solution Approach 1:
The patent maintains high Quality factor while controlling stop band response by strategically placing high and low acoustic velocity films at specific locations. The low acoustic velocity film is positioned adjacent to the inclined IDT electrode where transverse mode suppression is needed, while the high acoustic velocity film is placed on the opposite side of the piezoelectric body layer to provide acoustic wave confinement and maintain high Quality factor.
Solution Approach 2:
The patent introduces intermediary layers (low acoustic velocity film and high acoustic velocity film) that mediate between the inclined IDT electrode and the external environment. These intermediary layers act as acoustic impedance transformers that control wave propagation, allowing the system to achieve both high Quality factor and suppressed stop band response.
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 or prevents transverse mode ripple and upper stop band response, resulting in improved filter characteristics and insertion loss, enhancing the overall performance of the acoustic wave device.
Implementation Method 1
a piezoelectric body layer including a first main surface and a second main surface opposing each other
Implementation Method 2
a high acoustic velocity member which is disposed on the first main surface of the piezoelectric body layer and in which an acoustic velocity of a bulk wave propagating therethrough is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric body layer
Data Source
AI summary
An acoustic wave device including series arm resonators including a first IDT electrode and parallel arm resonators including a second IDT electrode, in the first IDT electrode, a first envelope obliquely extends with respect to the acoustic wave propagation direction, and a second envelope obliquely extends with respect to the acoustic wave propagation direction, the second IDT electrode includes a central region, a first low acoustic velocity region in which an acoustic velocity is lower than an acoustic velocity in the central region, a second low acoustic velocity region in which an acoustic velocity is lower than the acoustic velocity in the central region, a first high acoustic velocity region in which an acoustic velocity is higher than the acoustic velocity in the central region, and a second high acoustic velocity region in which an acoustic velocity is higher than the acoustic velocity in the central region.