Bilayer Substrate for RF Power Devices with High Thermal Conductivity
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Solution Overview
Problem
Existing microelectronic devices for radiofrequency or power applications face challenges with substrates that have either low thermal conductivity due to thick silicon oxide layers or are costly, such as sapphire substrates, which hinder efficient heat dissipation and are expensive for larger diameters.
Innovation Solution
A support substrate with a bilayer structure comprising a high thermal conductivity base layer and a superficial layer with high electrical resistivity, such as AlN, alumina, or amorphous diamond-like carbon, is used, along with a thin silicon oxide layer to facilitate bonding and heat dissipation, allowing for the manufacture of large wafers with improved thermal properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick layer of silicon oxide is used in SOI substrates to achieve high electrical resistivity, then electrical resistivity is improved, but thermal conductivity deteriorates
Solution Approach 1:
The substrate is segmented into multiple functional layers: a first substrate providing mechanical support, a thin silicon oxide layer providing electrical isolation, and a second substrate providing thermal management. This segmentation allows each layer to optimize its specific function without compromising the others.
Solution Approach 2:
The invention uses a composite substrate structure combining different materials (silicon, silicon oxide, sapphire, diamond-like carbon) to achieve properties that no single material can provide alone. The composite structure integrates electrical isolation with high thermal conductivity.
2Temperature
If sapphire substrates are used to achieve high thermal conductivity and high electrical resistivity, then thermal conductivity is improved, but manufacturing cost deteriorates
Solution Approach 1:
High thermal conductivity is applied locally only where needed (in the second substrate layer for heat dissipation), while other areas use cost-effective materials. This allows optimization of thermal management without requiring expensive materials throughout the entire substrate structure.
Solution Approach 2:
The invention changes the material parameters selectively in different layers rather than using a uniform expensive material throughout. By adjusting material composition and thickness parameters, the system achieves required performance at lower overall cost.
3Ease of manufacture
If an oxide layer is inserted between the component layer and sapphire substrate to facilitate bonding, then ease of manufacture is improved, but thermal conductivity deteriorates
Solution Approach 1:
Instead of using a thick oxide layer that would provide excellent bonding but poor thermal conduction, the invention uses a thin oxide layer (5-50 nm) that provides sufficient bonding facilitation while minimizing thermal resistance. This partial action approach achieves the minimum necessary bonding function without excessive thermal insulation.
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
The solution provides a substrate with both high electrical resistivity and thermal conductivity, suitable for large wafers, enabling efficient heat dissipation and cost-effectiveness compared to sapphire substrates, while maintaining the required thermal expansion coefficient and temperature resistance for device manufacturing.
Implementation Method 1
a bonding layer consisting of a silicon oxide layer having a thickness of less than 50 nm, a layer of AIN, of alumina or of high-resistivity polycrystalline silicon
Implementation Method 2
A good thermal conductivity is necessary to discharge the heat generated by high-frequency or high-power device operation
Implementation Method 3
a high resistivity makes it possible to limit high-frequency interactions between transistors (the field line penetration in the substrate causing parasitic effects)
Data Source
Figure 1A~1D
Figure 1E~3
Figure 4A~4C
AI summary
The invention relates to an electronic device for radio frequency or power applications, comprising a semiconductor layer supporting electronic components on a support substrate, wherein the support substrate(1) comprises a base layer (12) having a thermal conductivity of at least 30 W/m K and a superficial layer (13, 4) having a thickness of at least 5 µm, said superficial layer (13, 14) having an electrical resistivity of at least 3000 Ohm.cm and a thermal conductivity of at least 30 W/m K. The invention also relates to two processes for manufacturing such a device.