SiC Substrate Parasitic Diode Freewheeling
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Solution Overview
Problem
The use of SiC-MOSFETs in inverters requires a separate freewheel diode, increasing device count and cost, and existing methods to reduce recombination energy, such as the recombination enhancing layer, face challenges like increased film thickness and difficulty in measuring impurity concentration and thickness, which affect device operation and cost.
Innovation Solution
A SiC semiconductor substrate with a first conductivity type substrate doped to have a specific resistance of 30 mΩcm or less and a minority carrier lifetime of 100 nsec or less is used, allowing the parasitic PN diode to function as a freewheel diode without the need for a separate diode, thereby reducing the influence of basal plane dislocations becoming stacking faults and improving device operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate freewheel diode is provided with the SiC-MOSFET, then the device can handle load current during switching, but the number of devices and cost increase
Solution Approach 1:
The patent merges the freewheel diode function into the SiC-MOSFET structure by utilizing the parasitic PN junction formed between the drift layer and base region. This integration eliminates the need for a separate freewheel diode component while maintaining the required switching performance and load current handling capability.
Solution Approach 2:
The SiC-MOSFET structure is designed to perform multiple functions: the main switching function through the MOSFET channel and the freewheel diode function through the parasitic PN junction. This multi-functionality allows a single device to replace what would traditionally require two separate components.
2Reliability
If a recombination enhancing layer is added to reduce recombination energy, then device operation is improved, but film thickness increases and impurity concentration measurement becomes difficult
Solution Approach 1:
The patent extracts and eliminates the recombination enhancing layer from the device structure. By using the parasitic PN junction inherent in the basic SiC-MOSFET structure, the need for this additional layer is removed, thereby simplifying the structure and making impurity concentration measurement straightforward without compromising device operation.
3Reliability
If minority carrier lifetime is reduced to prevent stacking faults, then device performance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent utilizes the self-inherent parasitic PN junction structure of the SiC-MOSFET to achieve the freewheel diode function. This approach leverages the existing material properties and structure rather than requiring additional manufacturing steps or precise control of minority carrier lifetime, thereby reducing manufacturing precision requirements while maintaining device reliability.
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 reduces the influence of recombination energy on device operation, simplifies manufacturing by eliminating the need for a recombination enhancing layer, and lowers manufacturing costs while maintaining low on-resistance and restricting the impact of basal plane dislocations on device performance.
Implementation Method 1
A lifetime of minority carriers in the first conductivity type substrate is set to 100 nsec or less. Therefore, it is possible to reduce influence of recombination energy on operation of the device
Data Source
AI summary
A silicon carbide semiconductor substrate includes a first conductivity type substrate doped with a first conductivity type impurity to have a first conductivity type and having a specific resistance of 30 mΩcm or less. A lifetime of minority carriers in the first conductivity type substrate is set to 100 nsec or less.