Acoustic Wave Filter Structure for Inductor Coupling Isolation
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Solution Overview
Problem
Capacitive coupling between the inductor and the silicon substrate interface in acoustic wave devices leads to increased insertion loss, particularly in filter devices.
Innovation Solution
Incorporating an amorphous silicon layer, polysilicon layer, or silicon nitride layer between the covering portion and the silicon oxide layer to trap electric carriers, thereby reducing or preventing capacitive coupling and insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon oxide film is used to provide electrical isolation between the spiral inductor and silicon substrate, then electrical isolation is improved, but low-resistance portions form at the interface causing capacitive coupling
Solution Approach 1:
An amorphous silicon layer or polysilicon layer is introduced as an intermediary between the silicon oxide film and the covering portion. This intermediate layer acts as a mediator that prevents the formation of low-resistance portions at the interface, thereby eliminating capacitive coupling while maintaining the electrical isolation function of the silicon oxide film.
Solution Approach 2:
The patent creates a composite structure consisting of multiple layers: silicon oxide film, amorphous silicon layer (or polysilicon layer), and covering portion. This composite material structure combines the advantages of each layer - the silicon oxide provides electrical isolation, while the amorphous silicon or polysilicon layer prevents low-resistance portion formation, achieving both electrical isolation and prevention of capacitive coupling.
2Reliability
If the inductor is provided on the silicon oxide layer, then electrical isolation is achieved, but insertion loss increases due to capacitive coupling
Solution Approach 1:
The amorphous silicon layer or polysilicon layer serves as an intermediary that eliminates the harmful capacitive coupling effect, thereby reducing insertion loss while preserving the electrical isolation function that enables the inductor to be provided on the silicon oxide layer.
Solution Approach 2:
The composite structure of silicon oxide film plus amorphous silicon layer (or polysilicon layer) provides both electrical isolation and prevention of capacitive coupling, enabling the inductor to operate with reduced insertion loss while maintaining proper electrical isolation.
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
Reduces or prevents capacitive coupling and insertion loss in acoustic wave devices, enhancing their performance in filter applications.
Implementation Method 1
capacitive coupling is likely to occur between the low-resistance portion and the spiral inductor
Implementation Method 2
an amorphous silicon layer or a polysilicon layer provided between the covering portion and the inorganic oxide layer
Implementation Method 3
a piezoelectric substrate including a piezoelectric layer
Data Source
AI summary
An acoustic wave device according to the present invention includes a piezoelectric substrate including a piezoelectric layer, a functional electrode provided on the piezoelectric layer, a first support layer provided on the piezoelectric substrate so as to surround the functional electrode, a covering portion provided on or above the first support layer and including a first main surface positioned on the functional electrode side and a second main surface opposite to the first main surface, a silicon oxide layer provided on the first main surface side of the covering portion, and an inductor provided on the silicon oxide layer and made of a wire. The covering portion is made of silicon. The acoustic wave device further includes one of an amorphous silicon layer and a polysilicon layer provided between the covering portion and the silicon oxide layer.