SiC Trench Gate Structure With Shielding for Stable Switching
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Solution Overview
Problem
There is a need to increase the range of possible applications for silicon carbide devices, which are currently limited by their on-state resistance and switching behavior.
Innovation Solution
A silicon carbide device with a stripe-shaped trench gate structure and a shielding region of a second conductivity type, where the shielding region is in contact with the gate structure across at least 20% of its length, reducing gate-to-drain capacitance and improving switching behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional trench gate structure is used in silicon carbide devices, then the device structure is simple and manufacturing is easier, but the turn-off oscillation tendency is high and switching behavior is poor
Solution Approach 1:
The gate structure is segmented into multiple functional regions: an active gate sidewall for channel formation, an inactive gate sidewall, a bottom surface, and corner regions. This segmentation allows each region to be optimized independently, with the corner regions and bottom edges providing shielding effects that reduce turn-off oscillations while maintaining simple manufacturing processes.
Solution Approach 2:
Different regions of the gate structure are given different functional qualities. The active gate sidewall is optimized for channel formation and control, while the inactive gate sidewall and bottom edges are optimized for shielding and reducing oscillations. This local differentiation improves switching behavior without requiring complex overall structure changes.
2Strength
If the gate structure is extended deeper into the silicon carbide body, then the blocking voltage capability is improved, but the gate-to-drain capacitance increases causing higher turn-off oscillations
Solution Approach 1:
The harmful capacitive coupling between gate and drain is extracted and eliminated by using an inactive gate sidewall that does not extend fully to the bottom. This sidewall is taken out from the active channel-forming structure, allowing the gate to extend deeper for voltage blocking while the inactive portion prevents oscillations by not forming capacitive coupling with the drain region.
Solution Approach 2:
The inactive gate sidewall acts as an intermediary structure between the active gate region and the drain. It provides electrical isolation and shielding, mediating the interaction between the deep gate structure and the drain to prevent harmful capacitive coupling while maintaining the voltage blocking capability.
3Loss of energy
If silicon carbide devices are made thinner to reduce on-state resistance, then the on-state resistance is reduced, but the dielectric breakdown field strength requirements become more critical
Solution Approach 1:
The gate structure is designed with shielding regions and inactive sidewalls before the device operates, preliminarily preventing the formation of high electric field concentrations that could cause dielectric breakdown. This preliminary structural arrangement allows thinner devices to operate safely by preventing field enhancement at critical locations.
Data Source
AI summary
A silicon carbide device includes: a transistor cell having a stripe-shaped trench gate structure extending from a first surface into a silicon carbide body, the gate structure having a gate length along a lateral first direction, a bottom surface and a first gate sidewall of the gate structure being connected via a first bottom edge of the gate structure; at least one source region of a first conductivity type in contact with the first gate sidewall; and a shielding region of a second conductivity type in contact with the first bottom edge of the gate structure across at least 20% of the gate length. No source regions of the first conductivity type are in contact with a second gate sidewall of the gate structure.