Rayleigh-Wave Multiplexer Structure for Spurious Response Suppression
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Solution Overview
Problem
Acoustic wave devices used in multiplexers for communication systems suffer from spurious responses at higher frequencies, which degrade the filter characteristics of band pass filters, especially when multiple frequency bands are used in carrier aggregation.
Innovation Solution
A multiplexer design incorporating an acoustic wave device with a lithium niobate piezoelectric body, utilizing Rayleigh waves, and specific Euler angles, along with a low-acoustic-velocity material layer and a high-acoustic-velocity material layer to confine acoustic waves, and an IDT electrode made of materials like Pt, Al, Cu, or Au to reduce spurious responses and maintain filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If acoustic wave devices with high-acoustic-velocity support substrates are used in multiplexers, then the device can operate at higher frequencies, but spurious responses are generated that degrade filter characteristics
Solution Approach 1:
A low-acoustic-velocity film is introduced as an intermediary layer between the high-acoustic-velocity support substrate and the piezoelectric film. This mediator layer has acoustic velocity lower than both the support substrate and the piezoelectric film, creating acoustic impedance mismatch that prevents bulk waves from propagating into the piezoelectric film, thereby eliminating spurious responses while maintaining high-frequency operation
Solution Approach 2:
The acoustic velocity parameter of the support substrate is increased to enable higher frequency operation, while the acoustic velocity parameter of the intermediate film is decreased to block spurious bulk waves. By changing these material parameter selections, the patent resolves the contradiction between operating frequency and spurious response generation
2Adaptability or versatility
If band pass filters for lower frequency bands are used in carrier aggregation, then multi-band communication is enabled, but spurious responses from lower band filters interfere with higher band filters
Solution Approach 1:
The low-acoustic-velocity film acts as a mediator that isolates the acoustic wave propagation in each band pass filter, preventing spurious responses from one filter from interfering with other filters. This enables reliable multi-band operation by ensuring that each filter's spurious responses are contained and do not degrade the characteristics of filters operating in different frequency bands
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 reduces or prevents spurious responses at lower frequencies, ensuring that the filter characteristics of higher frequency band pass filters are not degraded, making the multiplexer suitable for carrier aggregation applications.
Implementation Method 1
The acoustic wave device utilizes Rayleigh waves
Implementation Method 2
The piezoelectric body is made of lithium niobate
Implementation Method 3
a low-acoustic-velocity material layer that is provided between the support substrate and the piezoelectric body... in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of an acoustic wave propagating along the piezoelectric body
Data Source
AI summary
A multiplexer includes a common terminal, a first band pass filter that is connected to the common terminal and has a first pass band, and a second band pass filter that is connected to the common terminal and has a second pass band located at higher frequencies than the first pass band. The first band pass filter includes an acoustic wave device that includes a support substrate, a piezoelectric body stacked on the support substrate, and an IDT electrode provided on the piezoelectric body. The piezoelectric body is made of lithium niobate. The acoustic wave device utilizes Rayleigh waves.