Surface Acoustic Wave Device Electrode Structure Void Prevention
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Solution Overview
Problem
Surface acoustic wave devices face issues with void generation in interdigital transducers due to thermal stress, leading to increased power resistance and resonance frequency variations, which affects their performance in mobile communication terminals.
Innovation Solution
A surface acoustic wave device with a thin-film structure featuring a base layer of TiN or TiOxNy and a second base layer of Cr between the interdigital transducer and the piezoelectric substrate, along with a CuAg alloy main electrode layer, to prevent void generation and enhance adhesion, power resistance, and reduce resonance frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the interdigital transducers and piezoelectric substrate are covered with a silicon oxide layer to reduce resonance frequency variations, then the temperature stability is improved, but voids are generated in the interdigital transducers due to thermal stress
Solution Approach 1:
The electrode structure is segmented into multiple functional layers: a base layer (Al or Al alloy) directly on the piezoelectric substrate, and a main electrode layer (Cu or Cu alloy) on top of the base layer. This segmentation allows each layer to perform its specific function - the base layer provides thermal expansion compatibility and adhesion, while the main electrode layer provides electrical conductivity, thereby preventing void generation while maintaining resonance frequency stability.
Solution Approach 2:
The patent uses composite material structure with a base layer of Al or Al alloy (containing Si, Fe, or Cu in specific amounts) combined with a main electrode layer of Cu or Cu alloy. This composite structure combines the advantages of both materials - Al's thermal expansion compatibility with the piezoelectric substrate and Cu's excellent electrical conductivity, preventing void generation while maintaining electrical performance and temperature stability.
2Device complexity
If a simple interdigital transducer structure is used to reduce device size, then the device complexity is reduced, but power resistance and reliability deteriorate due to void formation
Solution Approach 1:
The electrode is segmented into a base layer and a main electrode layer, where the base layer (Al or Al alloy) provides mechanical stability and thermal compatibility, while the main electrode layer (Cu or Cu alloy) provides high electrical conductivity. This segmentation prevents void formation and improves power resistance without significantly increasing device complexity.
Solution Approach 2:
The composite electrode structure uses Al or Al alloy as the base layer and Cu or Cu alloy as the main electrode layer. This composite material approach combines the thermal expansion advantages of Al with the electrical conductivity advantages of Cu, achieving high power resistance and reliability while maintaining a relatively simple overall structure suitable for mobile communication terminals.
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
The solution effectively prevents voids, reduces power loss, and stabilizes resonance frequencies, improving the device's power resistance and Q-factor, while preventing electrode peeling and electromigration.
Implementation Method 1
a base layer and a main electrode layer laminated on the base layer. The base layer has a first base layer made of TiN or TiOxNy... by providing the first base layer made of TiN or TiOxNy, it is possible to prevent voids from being generated in the interdigital transducer portions
Implementation Method 2
Surface acoustic wave devices are electronic components using surface acoustic waves which are propagated in a state in which mechanical vibration energy is concentrated around only surfaces of solid substances
Implementation Method 3
a pair of interdigital transducers (IDT electrodes) made of a conductive material is disposed on a piezoelectric substrate
Implementation Method 4
it has been known that the interdigital transducers and the piezoelectric substrate are covered with a silicon oxide layer so as to reduce the variations in the serial resonance frequency and the parallel resonance frequency due to the temperature change
Data Source
AI summary
First base layers made of TiN or TiOxNy (where, 0<x<0.2, x+y=1) and second base layers made of Cr are provided between interdigital transducer portions and a piezoelectric substrate, and accordingly, it is possible to prevent voids from being generated in the interdigital transducer portions, which improves a power resistance of the surface acoustic wave device. In addition, since it is possible to prevent the voids from being generated in the interdigital transducer portions, it is possible to suppress the resistance of the interdigital transducer portions from increasing, which can reduce the loss of power. In addition, it is also possible to reduce the variations in a serial resonance frequency and a parallel resonance frequency.