Acoustic Wave Filter Layer Structure to Limit Adjacent-Band Ripple
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Solution Overview
Problem
Acoustic wave resonators with a lithium tantalate film laminated on a silicon substrate tend to generate spurious responses, which can deteriorate the filter characteristics of adjacent acoustic wave filters with different pass bands.
Innovation Solution
The acoustic wave device is designed with a specific configuration including a silicon support substrate, a silicon oxide film, a lithium tantalate film, an IDT electrode, and a protection film, where the film thicknesses and Euler angles are optimized to ensure that a value represented by a specific formula is greater than -2.4, minimizing ripple generation in adjacent filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a lithium tantalate film is laminated directly on a silicon support substrate, then the device structure is simple and manufacturing is easy, but spurious responses appear on the higher frequency side which deteriorate filter characteristics
Solution Approach 1:
An aluminum oxide film is introduced as an intermediary layer between the lithium tantalate film and the silicon support substrate. This intermediary layer prevents the generation of spurious responses while maintaining the overall simplicity of the device structure and manufacturing process.
Solution Approach 2:
The patent creates a composite structure consisting of multiple layers (silicon support substrate, aluminum oxide film, lithium tantalate film) with specific thickness ratios. This composite material approach eliminates spurious responses by carefully controlling the interaction between different materials through optimized thickness parameters.
2Adaptability or versatility
If multiple acoustic wave filters with different frequencies are connected in common, then the device functionality is enhanced, but spurious responses from one filter may appear in the pass band of another filter
Solution Approach 1:
The aluminum oxide film acts as a mediator that prevents spurious responses from one filter from interfering with the pass band of adjacent filters, thereby enabling multiple filters to operate in common without mutual interference.
Solution Approach 2:
By optimizing the thickness parameters of the aluminum oxide film and lithium tantalate film according to specific formulas, the patent suppresses spurious responses across different frequency ranges, allowing multiple filters with different pass bands to coexist without interference.
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 spurious responses and improves the filter characteristics of acoustic wave devices by optimizing the film thicknesses and angles, thereby enhancing the performance of acoustic wave filters.
Implementation Method 1
a piezoelectric substrate made of lithium tantalate
Implementation Method 2
surface acoustic wave resonators
Implementation Method 3
Bonding in the (111) plane of silicon enhances the heat resistance
Data Source
AI summary
An acoustic wave device includes a silicon oxide film, a lithium tantalate film, an IDT electrode, and a protection film that are laminated on a support substrate made of silicon. A wavelength normalized film thickness of a lithium tantalate film is denoted by TLT, an Euler angle is θLT, a wavelength normalized film thickness of the silicon oxide film is TS, a wavelength normalized film thickness of the IDT electrode in terms of aluminum thickness is TE, a wavelength normalized film thickness of a protection film is TP, a propagation direction in the support substrate is ψSi, and a wavelength normalized film thickness of the support substrate is TSi. Values of TLT, θLT, TS, TE, TP, and ψSi are set such that Ih corresponding to an intensity of a response of a spurious response represented by Formula (1) is greater than about −2.4 in a spurious response.