Multilayer IDT Electrode Structure for High-Q Acoustic Wave Devices
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Solution Overview
Problem
Existing acoustic wave devices have limitations in achieving sufficient Q values due to the relatively low Young's modulus of Al electrodes, which restricts the performance of these devices in applications requiring higher Q characteristics.
Innovation Solution
The acoustic wave device incorporates a multilayer IDT electrode with a high acoustic impedance metal layer, such as Mo, W, or Ru, located closer to the piezoelectric layer, and an Al metal layer, where the high impedance metal layer has a Young's modulus of at least 200 GPa, and the normalized film thickness of the electrode fingers is optimized to improve the Q characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a generally known Al electrode is applied as the IDT electrode, then the device structure is simple and easy to manufacture, but the Q value is limited and sometimes insufficient for the desired Q value
Solution Approach 1:
The patent applies composite materials by creating a multilayer IDT electrode structure combining Al metal layer and high acoustic impedance metal layer. This composite structure leverages the low acoustic velocity of Al and the high acoustic impedance of metals like Mo, W, or Ru to achieve superior Q values while maintaining manufacturability through established sputtering processes
Solution Approach 2:
The patent employs parameter changes by optimizing the film thicknesses of each layer in the multilayer electrode structure. By controlling the thickness of the Al metal layer and high acoustic impedance metal layer within specific ranges, the device achieves desired Q values while maintaining ease of manufacture through precise deposition control
2Ease of manufacture
If the Young's modulus of Al is used in the IDT electrode, then the manufacturing process is simple, but the Q value that can be obtained is limited
Solution Approach 1:
The patent uses composite materials to overcome the limited Q value of pure Al electrodes. By combining Al metal layer with high acoustic impedance metal layer (Mo, W, or Ru), the structure achieves high Q values while maintaining simple manufacturing processes using conventional sputtering techniques
Solution Approach 2:
The patent applies local quality by assigning different material properties to different layers of the IDT electrode. The Al metal layer provides low acoustic velocity in its specific region, while the high acoustic impedance metal layer provides high acoustic impedance where needed, optimizing overall device performance
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 the Q characteristics and reduces energy loss, allowing for improved performance by stabilizing the Q value and optimizing energy confinement within the piezoelectric layer.
Implementation Method 1
a high acoustic impedance metal layer, such as Mo, W, or Ru, located closer to the piezoelectric layer, wherein the high impedance metal layer has a Young's modulus of at least 200 GPa
Implementation Method 2
a piezoelectric layer on the energy confinement layer and made of Y-cut X-propagation lithium tantalate
Data Source
AI summary
An acoustic wave device includes an energy confinement layer, a piezoelectric layer made of Y-cut X-propagation lithium tantalate having a cut angle in a range from about −10° to about 65°, and an IDT electrode. Electrode fingers of the IDT electrode include an Al metal layer and a high acoustic impedance metal layer having a Young's modulus equal to or more than about 200 GPa and an acoustic impedance higher than Al. The high acoustic impedance metal layer is closer to the piezoelectric layer than the Al metal layer. A wavelength specific film thickness tLT of the piezoelectric layer is expressed by tLT≤1λ. The total of normalized film thicknesses obtained by normalizing the film thickness of each layer of the electrode finger by a density and Young's modulus of the Al metal layer satisfies T≤0.1125tLT+0.0574.