Acoustic Wave Filter Stack With Resistivity-Graded Substrate
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Solution Overview
Problem
Existing acoustic wave devices face challenges in easily adjusting fractional band width and maintaining filter characteristics, leading to potential deterioration.
Innovation Solution
The use of a semiconductor substrate with a high acoustic velocity material, a low acoustic velocity film, and a piezoelectric thin film, along with an IDT electrode, allows for effective energy confinement and easy adjustment of fractional band width by incorporating a low resistance region and specific film thickness configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a conductive film is added to improve temperature characteristics, then temperature stability is improved, but device complexity increases and fractional band width adjustment becomes difficult
Solution Approach 1:
The invention changes the electrical resistance parameter of the semiconductor substrate by creating a first region with lower electric resistance than the second region. This parameter change enables the substrate to provide temperature compensation functionality without requiring an additional conductive film layer, thus improving temperature characteristics while avoiding increased device complexity
Solution Approach 2:
The semiconductor substrate is designed to serve multiple functions: it acts as both the structural support and the temperature compensation element through its differentiated resistance regions. This multi-functionality eliminates the need for separate conductive film layers used for temperature compensation in conventional designs
2Reliability
If film thickness is increased to improve filter characteristics, then energy confinement is improved, but device size increases
Solution Approach 1:
The invention optimizes the thickness parameter of the piezoelectric thin film to achieve effective energy confinement while maintaining compact device dimensions. By carefully controlling the film thickness parameter and combining it with the differentiated resistance substrate structure, the invention achieves improved filter characteristics without proportionally increasing device size
Solution Approach 2:
The invention uses a composite structure combining the piezoelectric thin film with the semiconductor substrate that has spatially varying resistance properties. This composite material approach enables enhanced energy confinement and improved filter characteristics while maintaining a compact overall device size
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 enables precise control over fractional band width and enhances the steepness of the pass band filter, improving filter characteristics and reducing device size while maintaining resonant frequencies.
Implementation Method 1
a piezoelectric thin film provided directly on or indirectly above the first main surface of the semiconductor substrate
Implementation Method 2
an IDT electrode provided on the piezoelectric thin film
Implementation Method 3
An acoustic velocity of a bulk wave propagating through the high acoustic velocity film is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric thin film
Implementation Method 4
The conductive film is provided to significantly improve the temperature characteristics of the acoustic wave device by the electric field short circuit effect
Data Source
AI summary
An acoustic wave device includes a semiconductor substrate having a first main surface and a second main surface, a piezoelectric thin film provided directly on or indirectly above the first main surface of the semiconductor substrate, and an IDT electrode provided on the piezoelectric thin film. A semiconductor defining the semiconductor substrate is a high acoustic velocity material in which an acoustic velocity of a bulk wave propagating therethrough is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric thin film. The semiconductor substrate includes a first region including the first main surface and a second region which is a region other than the first region and includes the second main surface. An electric resistance of the first region is lower than an electric resistance of the second region.