Epitaxial Silicon on Flexible Substrates via IBAD Buffer
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Solution Overview
Problem
Current semiconductor devices face challenges in achieving high carrier mobility and low carrier concentration levels, particularly when fabricating silicon films on flexible substrates, as existing methods like e-beam evaporation on r-plane alumina suffer from lattice mismatch and fail to exceed mobility of 100 cm2/Vs or carrier concentration below 1016 cm−3.
Innovation Solution
A semiconductor device is fabricated using a flexible substrate with a buffer stack comprising a biaxially-textured Ion Beam-Assisted Deposition (IBAD) layer and an epitaxial doped layer predominantly of silicon, grown via plasma enhanced chemical vapor deposition, achieving mobility greater than 100 cm2/Vs and carrier concentration less than 1016 cm−3, with an epitaxial undoped layer of silicon added for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If e-beam evaporation process is used to fabricate epitaxial silicon on r-plane alumina, then silicon films can be grown on flexible substrates, but the lattice mismatch limits mobility to below 100 cm2/Vs and carrier concentration cannot be reduced below 1016 cm−3
Solution Approach 1:
The patent introduces an intermediary buffer stack comprising multiple layers (Al2O3, Y2O3, MgO, LaMnO3, CeO2, and epitaxial germanium) between the flexible substrate and the silicon film. This buffer stack acts as a mediator to gradually transition from the alumina substrate lattice to the silicon lattice, reducing the mismatch and enabling high mobility (>100 cm2/Vs) and low carrier concentration (<1016 cm−3) in the epitaxial silicon layer.
2Reliability
If crystalline silicon fabrication platforms are used, then high mobility (>100 cm2/Vs) can be achieved, but the cost is high and the form factor is not adequate for large scale flexible electronics
Solution Approach 1:
The patent changes the substrate parameter from rigid single-crystal wafers to flexible metal substrates with amorphous or polycrystalline buffer layers. By modifying the substrate flexibility and using ion beam-assisted deposition followed by epitaxial growth, the process achieves crystalline-like mobility on flexible, cost-effective substrates suitable for large-area electronics.
Solution Approach 2:
The patent replaces the conventional mechanical vapor deposition or liquid-phase epitaxy with ion beam-assisted deposition and plasma-enhanced chemical vapor deposition. This substitution enables precise control of film quality and crystal orientation on flexible substrates, achieving high mobility without requiring expensive single-crystal wafer fabrication infrastructure.
3Ease of manufacture
If amorphous silicon is used for flexible electronics, then low cost and flexibility are achieved, but carrier mobility is limited to 1-10 cm2/Vs which is far inferior to crystalline silicon
Solution Approach 1:
The patent segments the silicon film formation into two distinct stages: first forming an amorphous or polycrystalline buffer layer on the flexible substrate, then growing a high-quality epitaxial crystalline silicon layer on top. This segmentation allows the bottom layer to provide flexibility and the top layer to provide high mobility (>100 cm2/Vs), combining the advantages of both amorphous and crystalline silicon.
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 approach results in a semiconductor device with significantly improved carrier mobility and reduced carrier concentration, comparable to crystalline silicon, while being cost-effective and suitable for large-area flexible electronics, overcoming the limitations of previous methods.
Implementation Method 1
a buffer stack overlying the substrate, wherein the buffer stack comprises at least one epitaxial buffer layer... a biaxially-textured Ion Beam-Assisted Deposition (IBAD) layer
Implementation Method 2
an epitaxial doped layer comprised predominantly of silicon and overlying the at least one epitaxial buffer layer, grown via plasma enhanced chemical vapor deposition
Data Source
AI summary
A semiconductor device and method for fabricating same is disclosed. Embodiments are directed to a semiconductor device and fabrication of same which include a flexible substrate and a buffer stack overlying the substrate. The buffer stack comprises at least one epitaxial buffer layer. An epitaxial doped layer comprised predominantly of silicon overlies the at least one epitaxial buffer layer. Mobility of the device is greater than 100 cm2/Vs and carrier concentration of the epitaxial doped layer is less than 1016 cm−3.