Coupled Resonator Filter Tuning for Bandwidth and Return Loss
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Solution Overview
Problem
In coupled resonator filters, the buried layers cannot be trimmed directly to achieve optimal frequency position, bandwidth, and return loss performance due to their inaccessible nature, relying heavily on precise thickness control and modeling, which is challenging for high-yield production.
Innovation Solution
Incorporating a tunable capacitor structure that allows adjustment of return loss and bandwidth by changing the electrical boundary conditions, enabling trimming of filter response after final fabrication through direct feedback, using tuning capacitors connected across piezoelectric layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If precise thickness control and modeling are used for buried layers, then filter characteristics (frequency position, bandwidth, return loss) are improved, but manufacturing complexity and difficulty increase due to inaccessibility of buried layers for trimming
Solution Approach 1:
The patent introduces an acoustic matching layer as an intermediary element between the substrate and the piezoelectric layers. This matching layer serves as a controllable parameter that indirectly influences the filter characteristics without requiring direct access to or trimming of the buried layers. By adjusting the thickness or properties of this intermediate layer, the electrical boundary conditions are modified, thereby tuning the filter response while avoiding the complexity of trimming inaccessible buried layers.
2Ease of operation
If trimming is performed on accessible layers only, then ease of operation is improved, but manufacturing precision deteriorates because buried layers cannot be adjusted
Solution Approach 1:
The acoustic matching layer acts as a mediator that translates easy-to-perform trimming operations on accessible layers into precise control of filter characteristics. By trimming the matching layer, which is accessible after final fabrication, operators can indirectly and precisely control the electrical boundary conditions and thus the filter response, achieving high manufacturing precision without the need to access buried layers.
Solution Approach 2:
The patent utilizes parameter changes in the acoustic matching layer (such as thickness, material composition, or acoustic impedance) to control the electrical boundary conditions. By varying these parameters, the filter characteristics can be precisely tuned. This approach allows manufacturing precision to be achieved through simple parameter adjustment of an accessible layer rather than through complex trimming of inaccessible buried layers.
3Productivity
If high-yield production is pursued, then productivity is improved, but manufacturing precision must be increased to compensate for lack of post-fabrication trimming
Solution Approach 1:
The acoustic matching layer serves as a compensatory intermediary that can be adjusted to correct variations in buried layer thickness. By providing this additional controllable parameter, the system can accommodate higher variations in the fabrication of buried layers while still achieving the required filter specifications. This increases productivity by allowing higher yield without sacrificing final performance.
Solution Approach 2:
The patent incorporates the acoustic matching layer as a pre-planned compensatory element that cushions against potential variations in buried layer fabrication. By designing this intermediate layer with adjustable parameters, the system proactively prepares for and compensates for manufacturing variations, thereby maintaining high yield and productivity without requiring extremely tight process control on all layers.
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 approach improves return loss and bandwidth performance by allowing post-fabrication tuning, balancing center lobe and side lobes, and stabilizing frequency positions, thus enhancing production yield and reducing variations.
Implementation Method 1
a first piezoelectric layer disposed over the first lower electrode, and a first upper electrode disposed over the first piezoelectric layer... a second piezoelectric layer disposed over the second lower electrode, a second upper electrode disposed over the second piezoelectric layer
Implementation Method 2
one or more acoustic reflector layers disposed over the substrate... one or more acoustic coupling layers disposed over the first upper electrode
Implementation Method 3
coupled resonator filter device... first lower electrode disposed over the one or more acoustic reflector layers... second lower electrode disposed over the one or more acoustic coupling layers
Data Source
AI summary
A coupled resonator filter device is disclosed. The coupled resonator filter device includes a substrate with one or more acoustic reflector layers disposed over the substrate, a first lower electrode disposed over the one or more acoustic reflector layers, a first piezoelectric layer disposed over the first lower electrode, and a first upper electrode disposed over the first piezoelectric layer. The coupled resonator filter device further includes one or more acoustic coupling layers disposed over the first upper electrode, a second lower electrode disposed over the one or more acoustic coupling layers, a second piezoelectric layer disposed over the second lower electrode, a second upper electrode disposed over the second piezoelectric layer, and a first tuning capacitor having a first upper plate coupled to the first upper electrode and a first lower plate coupled to the first lower electrode.