Trench Power MOSFET Channel Doping Gradient
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Solution Overview
Problem
Trench power MOSFETs face challenges in achieving low on-state resistance while avoiding short channel effects and high subthreshold slope, which are exacerbated by the need for reduced channel length that degrades mobility and increases threshold voltage.
Innovation Solution
A trench power field effect transistor design with a channel length that satisfies a specific inequality, ensuring direct contact between the channel and base layers, and a doping concentration gradient, which maintains low on-state resistance and avoids short channel effects by optimizing the thickness and doping levels of the channel and base regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the channel length is reduced to achieve low on-state resistance, then the on-state resistance decreases, but short channel effects and high subthreshold slope are exacerbated
Solution Approach 1:
The patent applies local quality by creating a doping concentration gradient within the channel region, where the doping concentration varies from the source end to the drain end. Specifically, the channel has a lower doping concentration near the source and a higher doping concentration near the drain, which locally optimizes different regions to reduce on-state resistance while maintaining electrostatic control and avoiding short channel effects.
Solution Approach 2:
The patent changes the doping concentration parameter along the channel length, creating a graded channel where the doping concentration increases from source to drain. This parameter change allows the channel to simultaneously achieve low resistance (through higher doping near drain) and good electrostatic control (through lower doping near source), resolving the contradiction between reducing on-state resistance and avoiding short channel effects.
2Productivity
If the channel length is reduced to improve drive capability, then the drive capability increases, but the threshold voltage increases and mobility degrades
Solution Approach 1:
The patent uses local quality by differentiating the doping concentration at different locations along the channel. The source-end channel has lower doping to maintain low threshold voltage and high mobility, while the drain-end channel has higher doping to support high drive capability. This spatial differentiation of doping quality allows simultaneous optimization of threshold voltage control and drive capability.
Solution Approach 2:
The patent implements parameter changes by varying the doping concentration along the channel length, creating a graded profile that transitions from lower doping near the source to higher doping near the drain. This continuous parameter change enables the channel to achieve both low threshold voltage (from source-end low doping) and high drive capability (from drain-end high doping).
3Loss of energy
If a higher doping concentration is used in the channel to reduce on-state resistance, then the on-state resistance decreases, but the subthreshold slope increases
Solution Approach 1:
The patent applies local quality by creating different doping concentrations at different locations in the channel. The source-end channel region has lower doping concentration to maintain good subthreshold slope, while the drain-end channel region has higher doping concentration to reduce on-state resistance. This local differentiation resolves the contradiction between low on-state resistance and low subthreshold slope.
Solution Approach 2:
The patent changes the doping concentration parameter along the channel, creating a graded profile that increases from source to drain. This parameter gradient allows the channel to achieve both low on-state resistance (through higher average doping) and low subthreshold slope (through lower doping near the source where the channel is formed).
Data Source
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AI summary
The power semiconductor device according to the invention is a trench power field effect transistor, at all locations within a channel region a first local doping concentration is less than 1·1017 cm-3. In the base layer a second local doping concentration is at least 1·1017 cm-3 at all locations within the base layer. In the invention a channel length LCH, fulfils the following inequation: (I), wherein ε CH is a permittivity of the channel region, ε GI is a permittivity of the gate insulation layer, t CH is a thickness of the channel region in a direction perpendicular to an interface between the gate insulation layer and the channel region, and t GI is a thickness of the gate insulation layer in a direction perpendicular to the interface between the gate insulation layer and the channel region.