SiC Graded Channel Structure for Stable Threshold Voltage
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Solution Overview
Problem
As SiC power devices scale down, issues such as threshold voltage instability and punch-through effects arise due to geometrical profiles and high interface state density, affecting channel mobility and on-resistance.
Innovation Solution
A graded channel with a lightly doped and heavily doped region is implemented, featuring a retrograde well and a pocket, along with a self-aligned implantation process to form the heavily doped pocket without a tilt angle, enhancing threshold voltage control and preventing punch-through.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If device dimensions are scaled down, then device size is reduced, but threshold voltage stability deteriorates
Solution Approach 1:
The patent applies local quality by creating a graded channel with spatially varying dopant concentrations. The channel region has different dopant concentrations at different positions (higher near the drain, lower near the source), allowing localized control of electrical properties to maintain threshold voltage stability despite overall device scaling.
Solution Approach 2:
The patent changes the dopant concentration parameter along the channel length to create a graded profile. This parameter variation compensates for short-channel effects and maintains stable threshold voltage in scaled-down devices by adjusting the electrical characteristics locally along the channel.
2Volume of moving object
If device dimensions are scaled down, then device size is reduced, but on-resistance increases
Solution Approach 1:
The graded channel structure provides local quality optimization by having higher dopant concentrations near the drain region where electric field intensity is higher, reducing on-resistance locally where it is most critical, while maintaining lower concentrations near the source to control threshold voltage.
Solution Approach 2:
The patent introduces a gradient dimension along the channel length, transforming the uniform one-dimensional channel into a structured channel with varying properties. This additional spatial variation dimension allows simultaneous optimization of on-resistance and threshold voltage control.
3Volume of moving object
If device dimensions are scaled down, then device size is reduced, but punch-through effects worsen
Solution Approach 1:
The graded channel structure provides preliminary anti-action against punch-through effects by pre-establishing a dopant concentration gradient that counteracts the high electric field near the drain before punch-through can occur. The higher dopant concentration in the drain region creates a potential barrier that prevents carrier punch-through.
4Ease of manufacture
If uniform dopant concentration is used, then manufacturing is simpler, but channel mobility decreases
Solution Approach 1:
The patent applies local quality by implementing different dopant concentrations in different channel regions. The graded profile with higher concentrations near the drain and lower concentrations near the source optimizes channel mobility by reducing scattering in the low-field region while maintaining control in the high-field region.
Data Source
AI summary
A power device includes a silicon carbide substrate. A gate is provided on a first side of the silicon carbide substrate. A graded channel includes a first region having a first dopant concentration and a second region having a second dopant concentration, the second dopant concentration being greater than the first dopant concentration.