SiC MOSFET Gate Oxide Thickness for ESD Ruggedness
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Solution Overview
Problem
MOSFETs using SiC wafers have low channel mobility and thin gate oxide films, leading to reduced electrostatic discharge ruggedness, especially in current-sensor cell portions, which can result in improper overcurrent detection during assembly processes.
Innovation Solution
A semiconductor device structure with a thicker gate oxide film in the current-sensor cell portion compared to the source cell portion, improving electrostatic discharge ruggedness while maintaining equivalent output characteristics through adjustments in impurity concentration, channel length, and cell size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the gate oxide film is formed thinner to reduce ON resistance in SiC-MOSFETs, then the ON resistance decreases, but the electrostatic discharge ruggedness between gate and source decreases
Solution Approach 1:
The patent applies different gate oxide film thicknesses to different functional regions: the source cell portion uses a thinner gate oxide film (first thickness) to achieve low ON resistance for main current conduction, while the current-sensor cell portion uses a thicker gate oxide film (second thickness greater than first) to provide enhanced electrostatic discharge ruggedness for sensitive current sensing. This local differentiation resolves the contradiction by optimizing each region for its specific function.
2Measurement precision
If the number of unit cells in the current-sensor cell portion is reduced to 1/10000 to 1/5000 of the source cell portion, then the current sensor can detect 1/10000 to 1/5000 of the source current, but the electrostatic discharge ruggedness becomes much lower than the source cell portion
Solution Approach 1:
The patent implements local quality by making the gate oxide film thickness region-dependent: current-sensor cell portions have a thicker gate oxide film compared to source cell portions. This allows the current sensor to maintain high electrostatic discharge ruggedness despite having fewer unit cells and lower capacity, enabling proper overcurrent detection even in the presence of electrostatic discharge during assembly processes.
3Speed
If the gate oxide film is formed thinner, then the channel mobility increases, but the electrostatic discharge ruggedness between gate and source decreases
Solution Approach 1:
The patent applies local quality by differentiating gate oxide film thickness between functional regions: source cell portions use thinner gate oxide films to maximize channel mobility and conduction speed for main current, while current-sensor cell portions use thicker gate oxide films to ensure electrostatic discharge ruggedness for accurate current sensing. This resolves the contradiction between speed and reliability through spatial differentiation.
Data Source
AI summary
The present technique relates to a semiconductor device including a current sensor, which can improve the electrostatic discharge ruggedness. The semiconductor device includes: a first switching element through which a main current flows; and a second switching element through which a sense current flows. The first switching element includes a first gate oxide film formed in contact with a first base layer sandwiched between a first source layer and a drift layer. The second switching element includes a second gate oxide film formed in contact with a second base layer sandwiched between a second source layer and the drift layer. A part of the second gate oxide film including a portion covering the second base layer is thicker than the first gate oxide film.