RF Filter Substrate Bonding With Spin-On Glass Insulation
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Solution Overview
Problem
The assembly of piezoelectric layers with high thermal expansion coefficients on silicon substrates is challenging due to breakage or detachment during thermal annealing, cutting, and packaging, and existing methods require numerous steps to ensure adhesion on rough surfaces, making the process long and expensive.
Innovation Solution
A method involving centrifugal coating of an SOG oxide layer on the piezoelectric surface followed by annealing to densify the insulating layer before assembly, allowing direct bonding at room temperature or low heat, and using a silicon substrate with a trapping layer to enhance bonding energy and mechanical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal substrate is used to ensure mechanical strength and thermal conductivity, then structural stability is improved, but thermal expansion mismatch with ceramic capacitors causes cracking during firing
Solution Approach 1:
The substrate is divided into a metal base layer and a separate ceramic layer, with each layer optimized for its specific function. The metal provides mechanical strength while the ceramic layer accommodates thermal expansion differences, preventing cracks from propagating through the entire structure.
Solution Approach 2:
The invention uses a composite substrate structure combining metal and ceramic materials. This composite approach allows leveraging the high mechanical strength and thermal conductivity of metal while incorporating the low thermal expansion properties of ceramic to match capacitor materials, thereby resolving the thermal expansion mismatch issue.
2Stability of the object's composition
If a ceramic substrate is used to match thermal expansion properties, then thermal compatibility is improved, but mechanical strength and thermal conductivity are reduced
Solution Approach 1:
The substrate functionality is segmented between metal and ceramic layers. The metal base layer handles mechanical loading and heat dissipation, while the ceramic surface layer provides thermal expansion compatibility with capacitors, allowing each material to optimize its specific function.
Solution Approach 2:
By creating a metal-ceramic composite substrate, the invention combines the advantageous properties of both materials: the metal provides high mechanical strength and thermal conductivity, while the ceramic provides matched thermal expansion properties for reliable capacitor bonding.
3Use of energy by stationary object
If organic-inorganic hybrid sol-gel processing is used to achieve low processing temperatures, then energy consumption is reduced, but processing time and complexity increase
Solution Approach 1:
The invention changes the chemical composition parameters of the sol-gel precursor solution by adding specific organic modifiers and controlling pH, which fundamentally alters the drying and consolidation mechanisms. This enables low-temperature processing while maintaining simple procedural steps, resolving the trade-off between energy consumption and processing complexity.
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 method achieves strong bonding and maintains mechanical integrity, enabling processes like thinning and cutting while reducing parasitic wave reflections, thus improving the manufacturing efficiency and acoustic performance of radio frequency filters.
Implementation Method 1
depositing the electrically insulating layer by centrifugal coating of an oxide belonging to the SOG (Spin On Glass) family on the surface of the piezoelectric layer
Implementation Method 2
followed by annealing to densify said electrically insulating layer before assembly
Implementation Method 3
the surface of the piezoelectric layer located at the interface with the electrically insulating layer is sufficiently rough to allow reflection of parasitic waves in all directions
Implementation Method 4
An electrical signal, typically a variation in electrical voltage, applied to one electrode is converted into an elastic wave which propagates on the surface of the piezoelectric layer
Data Source
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AI summary
The invention relates to a method for manufacturing a substrate for a radiofrequency filter by assembling a piezoelectric layer on a support substrate via an electrically insulating layer, characterised in that it comprises the steps of: depositing the electrically insulating layer by spin coating an oxide belonging to the Spin On Glass (SOG) family onto the surface of the piezoelectric layer to be assembled on the support substrate, followed by annealing in order to densify said electrically insulating layer before assembly.