SiC Trench MOSFET JFET Compensation for Short-Circuit Capability
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Solution Overview
Problem
Conventional silicon carbide semiconductor devices, particularly trench gate MOSFETs, face challenges in short-circuit capability due to high on-resistance and thermal destruction during short-circuit events, as they cannot effectively manage large currents and high temperatures within the time frame required for protective circuits to operate.
Innovation Solution
The silicon carbide semiconductor device incorporates a JFET region doped with nitrogen and aluminum, where the effective donor concentration is adjusted based on temperature, increasing resistance during high temperatures to suppress short-circuit current while maintaining device on-resistance, thereby enhancing short-circuit capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the JFET region is doped with high concentration of donors to reduce on-resistance, then the on-resistance decreases, but the short-circuit current increases and thermal destruction occurs during short-circuit events
Solution Approach 1:
The patent applies parameter changes by doping the JFET region with both nitrogen (donor) and aluminum (acceptor) to precisely control the effective donor concentration. By adjusting the ratio and concentration of these dopants, the patent achieves an optimal balance where the JFET region has sufficiently low resistance for normal operation but increases resistance during high-temperature short-circuit conditions, thereby suppressing harmful short-circuit current while maintaining acceptable on-resistance
Solution Approach 2:
The patent converts the harmful effect of high temperature (which normally increases carrier concentration and reduces resistance) into a beneficial protective mechanism. During short-circuit events, the high temperature causes increased ionization of aluminum acceptors, which compensates the nitrogen donor concentration, thereby increasing the resistance of the JFET region and limiting the short-circuit current. This transforms thermal energy, normally a destructive factor, into a protective element that automatically limits fault current
2Object-generated harmful factors
If the JFET region length is reduced to suppress short-circuit current, then the short-circuit capability improves, but the on-resistance increases
Solution Approach 1:
The patent changes the doping parameters by introducing dual doping with nitrogen and aluminum in specific concentration ratios. This allows the JFET region to maintain low resistance through high nitrogen concentration while the aluminum concentration is optimized to provide temperature-dependent compensation. The effective donor concentration is controlled to be higher than the aluminum concentration, ensuring low on-resistance while enabling thermal protection during short-circuit events
3Reliability
If the effective donor concentration of the JFET region is increased to reduce on-resistance, then the on-resistance decreases, but the short-circuit current increases during thermal events
Solution Approach 1:
The patent implements parameter changes through controlled dual doping, where the effective donor concentration is set to be higher than the aluminum concentration but optimized to provide thermal protection. The nitrogen concentration provides low on-resistance while the aluminum concentration is sufficient to cause compensation at high temperatures, creating a resistance increase during short-circuit events that limits harmful current while maintaining low operating resistance
Solution Approach 2:
The patent transforms the potential harm of high effective donor concentration (which would normally increase short-circuit current) into a benefit by incorporating aluminum acceptors that become ionized at high temperatures. This thermal ionization of aluminum creates a compensating effect that increases resistance during short-circuit events, converting the high effective donor concentration from a liability into a protective feature that automatically limits fault current
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
This approach effectively reduces short-circuit current and improves short-circuit capability without increasing on-resistance, ensuring the device's reliability during thermal events.
Implementation Method 1
a JFET region doped with an acceptor that is aluminum and with a donor that is nitrogen or phosphorus, a concentration of the donor is greater than a concentration of the acceptor. The effective donor concentration of the JFET region is obtained by subtracting a concentration of the acceptor from a concentration of the donor.
Data Source
AI summary
A silicon carbide semiconductor device has an n-type silicon carbide semiconductor substrate, an n-type first semiconductor layer, n-type first JFET regions, a p-type second semiconductor layer, n-type first semiconductor regions, and trenches. The first semiconductor layer has an impurity concentration lower than that of the substrate. The first JFET regions are provided in a surface layer of the first semiconductor layer and have an effective donor concentration higher than that of the first semiconductor. The p-type second semiconductor layer is provided at a surface of the first semiconductor layer. The n-type first semiconductor regions are selectively provided in a surface layer of the second semiconductor layer. The trenches penetrate through the first semiconductor regions, the second semiconductor layer, and the first JFET regions. The first JFET regions are doped with an acceptor that is aluminum and a donor that is nitrogen or phosphorus.