RF Device Substrate Bonding with Photopolymer Adhesive Layers
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Solution Overview
Problem
The existing process for fabricating radiofrequency device substrates is costly and prone to substrate curvature due to high-temperature SiO2 depositions, requiring numerous steps and resulting in poor adhesion between the piezoelectric and carrier substrates, which complicates the production of flat substrates necessary for filter operations.
Innovation Solution
A process involving a piezoelectric substrate with a rough surface, a dielectric layer, and a photo-polymerizable adhesive layer is used to bond the piezoelectric substrate to a carrier substrate at low temperatures, eliminating the need for high-temperature SiO2 depositions and mechanical polishing, while ensuring good acoustic performance and reducing substrate bow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-temperature SiO2 deposition is used to ensure good adhesion between piezoelectric layer and carrier substrate, then adhesion quality is improved, but substrate curvature increases and production cost increases
Solution Approach 1:
The patent introduces an intermediary layer (adhesive layer) between the piezoelectric layer and carrier substrate to mediate the bonding process. This adhesive layer enables effective adhesion without requiring high-temperature SiO2 deposition, thus preventing substrate curvature while maintaining bond strength.
Solution Approach 2:
The patent changes the temperature parameter from high-temperature SiO2 deposition to low-temperature adhesive layer formation. This parameter change allows the bonding process to proceed at lower temperatures, eliminating thermal stress-induced curvature while achieving sufficient adhesion through the adhesive layer's chemical bonding properties.
2Strength
If multiple successive deposition and polishing steps are performed to ensure good adhesion on rough surfaces, then adhesion quality is improved, but manufacturing complexity and production time increase
Solution Approach 1:
The patent extracts and eliminates the complex multiple deposition and polishing steps from the manufacturing process. By using an adhesive layer that can effectively bond to rough surfaces, the process removes the need for intermediate SiO2 layers and CMP polishing steps, significantly simplifying the manufacturing workflow.
Solution Approach 2:
The adhesive layer serves as a disposable intermediate layer that simplifies the overall process. Rather than requiring multiple permanent structural layers (SiO2) and complex polishing operations, a single adhesive layer performs the bonding function, reducing both process complexity and production time.
3Strength
If multiple successive deposition and polishing steps are performed to ensure good adhesion, then adhesion quality is improved, but production cost increases
Solution Approach 1:
The patent removes the costly multiple deposition and polishing steps from the process. By using an adhesive layer that bonds effectively to rough surfaces, it eliminates the need for expensive SiO2 deposition equipment usage and CMP polishing operations, thereby reducing production costs while maintaining adhesion quality.
4Strength
If high-temperature SiO2 deposition is used, then adhesion is improved, but substrate flatness deteriorates due to thermal expansion differences
Solution Approach 1:
The patent changes the temperature parameter from high-temperature deposition to low-temperature adhesive bonding. This parameter change prevents thermal expansion mismatches between different substrate materials, maintaining substrate flatness while achieving adequate adhesion through the adhesive layer's room-temperature or low-temperature curing process.
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 reduces production costs, simplifies the bonding process, and minimizes substrate curvature, enabling the fabrication of radiofrequency devices with improved acoustic performance and reduced thermal frequency coefficients.
Implementation Method 1
the rough surface of the piezoelectric layer located at the interface with the electrically insulating layer rough enough to allow the parasitic waves to be reflected in all directions
Implementation Method 2
irradiating the assembled substrate with a light flux in order to polymerize the adhesive layer
Data Source
AI summary
A process for fabricating a substrate for a radiofrequency device by joining a piezoelectric layer to a carrier substrate by way of an electrically insulating layer, the piezoelectric layer having a rough surface at its interface with the electrically insulating layer, the process being characterized in that it comprises the following steps: —providing a piezoelectric substrate having a rough surface for reflecting a radiofrequency wave, —depositing a dielectric layer on the rough surface of the piezoelectric substrate, —providing a carrier substrate, —depositing a photo-polymerizable adhesive layer on the carrier substrate, —bonding the piezoelectric substrate to the carrier substrate by way of the dielectric layer and of the adhesive layer, in order to form an assembled substrate, —irradiating the assembled substrate with a light flux in order to polymerize the adhesive layer, the adhesive layer and the dielectric layer together forming the electrically insulating layer.