Elastic Wave Device Electrode Finger Design for Mode Suppression
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Solution Overview
Problem
Elastic wave devices used as resonators and band-pass filters face issues with high intensity in higher-order modes, where frequencies are higher than the fundamental frequency, leading to inefficiencies and unwanted spurious modes.
Innovation Solution
The elastic wave device incorporates a piezoelectric film, a high acoustic velocity member, and a low acoustic velocity film with an interdigital transducer electrode featuring a specific metal layer structure, including a recessed and protruding portion design, which reduces the intensity in higher-order modes by optimizing the acoustic velocity and energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low acoustic velocity film and piezoelectric film are stacked on a high acoustic velocity support substrate, then the device can function as a resonator or band-pass filter, but the intensity in higher-order modes becomes high
Solution Approach 1:
The electrode finger structure is modified locally by adding recessed portions and protrusion portions at specific locations. These local structural changes create specific acoustic impedance variations that suppress higher-order modes while maintaining fundamental mode operation, thereby resolving the contradiction between device functionality and higher-order mode intensity
Solution Approach 2:
The invention transitions from a two-dimensional electrode finger structure to a three-dimensional structure by adding recessed portions (going into the substrate) and protrusion portions (extending outward). This dimensional change allows for more effective control of acoustic wave propagation and suppression of higher-order modes
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 the intensity in higher-order modes, enhancing the Q-value and temperature characteristics, and improving the electromechanical coupling coefficient, leading to improved performance as a resonator or band-pass filter.
Implementation Method 1
a piezoelectric film... The interdigital transducer electrode is disposed on the principal surface of the piezoelectric film
Implementation Method 2
The acoustic velocity of an elastic wave that propagates through the high acoustic velocity support substrate is higher than the acoustic velocity of an elastic wave that propagates through the piezoelectric film. The acoustic velocity of an elastic wave that propagates through the low acoustic velocity film is lower than the acoustic velocity of an elastic wave that propagates through the piezoelectric film.
Data Source
AI summary
An elastic wave device includes a piezoelectric film, a high acoustic velocity member, a low acoustic velocity film located between the piezoelectric film and the high acoustic velocity member and through which an elastic wave propagates at a lower acoustic velocity than an elastic wave that propagates through the piezoelectric film, and an interdigital transducer electrode including electrode fingers separated from each other and disposed side by side in a first direction. At least one of the electrode fingers includes a first metal layer including first and second main body portions. A recessed portion is located in a central region in the first direction of the electrode finger and is recessed in the thickness direction of the piezoelectric film. A protrusion portion protrudes from at least a portion of the first main body portion in the first direction.