Acoustic Wave Filter Stack That Shifts Spurious Responses
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Solution Overview
Problem
Acoustic wave resonators with lithium tantalate films stacked on silicon substrates suffer from spurious responses that can degrade the filter characteristics of adjacent band pass filters, leading to ripples in the pass bands of higher frequency filters.
Innovation Solution
The acoustic wave device is designed with specific Euler angles and wavelength-normalized thicknesses for the lithium tantalate and silicon oxide films, IDT electrode, and protective film, ensuring that spurious responses are positioned outside the pass bands of other filters, preventing degradation of filter characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a lithium tantalate film is directly or indirectly stacked on a silicon support substrate to form an acoustic wave resonator, then heat resistance is improved, but spurious responses appear on the high-frequency side that can degrade filter characteristics of other band pass filters
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness of the silicon oxide film (0.05λ to 0.5λ) and the lithium tantalate film (0.5λ to 3.5λ), along with specific Euler angles (θLT: 120° to 180°, ψLT: -45° to 45°), to shift the frequency of spurious responses outside the pass bands of other filters, thereby resolving the contradiction between maintaining heat resistance and eliminating harmful spurious responses
Solution Approach 2:
The patent uses a composite structure consisting of multiple layers (silicon support substrate, silicon oxide film, lithium tantalate film, IDT electrode, and protective film) where each layer contributes specific properties. This composite material approach allows simultaneous achievement of heat resistance (from silicon substrate) and spurious response control (through the combined acoustic properties of the layered structure)
2Adaptability or versatility
If multiple band pass filters with different frequencies are connected forming a common connection, then radio-frequency signal routing is enabled, but spurious responses from lower frequency filters can appear in the pass bands of higher frequency filters causing ripples
Solution Approach 1:
The patent uses parameter changes in the acoustic wave resonator structure (film thicknesses and Euler angles) to control the frequency position of spurious responses, ensuring they fall outside the pass bands of other filters in the multi-filter system, thus maintaining reliable filter characteristics while enabling versatile signal routing
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 prevents spurious responses from occurring within the pass bands of higher frequency filters, maintaining excellent filter characteristics in radio-frequency front end circuits and communication devices.
Implementation Method 1
an acoustic wave resonator includes a silicon support substrate, a silicon oxide film stacked above the silicon support substrate, a lithium tantalate film stacked above the silicon oxide film
Implementation Method 2
a lithium tantalate film stacked above the silicon oxide film and having Euler angles (φLT=0°±5°, θLT, ψLT=0°±15°), an IDT electrode provided above the lithium tantalate film
Data Source
AI summary
An acoustic wave device includes N band pass filters with first ends connected to define a common connection and having different pass bands. At least one of the band pass filters includes acoustic wave resonators including a lithium tantalate film having Euler angles (φLT=0°±5°, θLT, ψLT=0°±15°), a silicon support substrate, a silicon oxide film between the lithium tantalate film and the silicon support substrate, an IDT electrode, and a protective film. In at least one acoustic wave resonator, a frequency fh1_t(n) satisfies Formula (3) or Formula (4) for all m where m>n:fh1_t(n)>fu(m) Formula (3); andfh1_t(n)<fl(m) Formula (4).In Formulas (3) and (4), fu(m) and fl(m) represent the frequencies of the high-frequency end and the low-frequency end of the pass band in the m band pass filters.