SGT MOSFET with Adjustable Bottom Electrode Connections
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Solution Overview
Problem
Conventional shielded gate trench (SGT) MOSFET devices face limitations due to high gate ringing, electromagnetic interference (EMI), and increased input capacitance (Ciss) when trying to reduce specific-on resistance and cell density, leading to tradeoffs that affect switching speed and loss.
Innovation Solution
The SGT MOSFET configuration is improved by flexibly adjusting the connections of bottom electrodes, where some are connected to the source metal and others to the gate metal, allowing for adjustable ratios to reduce ringing and EMI, with some bottom electrodes connected to the source and others to the gate, and top electrodes connected to the source or gate, to manage Crss and Ciss effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the gate-to-drain capacitance is reduced by implementing a shielded gate trench (SGT) configuration, then switching speed is improved and loss is reduced, but gate ringing and electromagnetic interference (EMI) increase
Solution Approach 1:
The shield gate trench structure is divided into multiple bottom electrodes with different connection configurations. Some bottom electrodes are connected to the source while others are connected to the gate, segmenting the capacitance control function to simultaneously achieve low Crss for high switching speed and controlled Crss to reduce gate ringing and EMI
Solution Approach 2:
Different bottom electrodes are assigned different connection types (source-connected or gate-connected) based on local requirements. This creates non-uniform local properties within the shield gate structure, allowing specific regions to contribute to reducing gate ringing and EMI while maintaining overall low Crss for high switching speed performance
2Loss of energy
If the cell density is increased with significantly reduced pitch to reduce specific-on resistance, then the specific-on resistance decreases, but the input capacitance (CISS) increases thus slowing down the turn on and off speeds
Solution Approach 1:
The invention introduces adjustable and flexible connection configurations for bottom electrodes that can be dynamically optimized for different operating conditions. The ratio of source-connected to gate-connected bottom electrodes can be adjusted to balance the tradeoff between specific-on resistance and input capacitance, enabling high cell density while maintaining fast switching speeds
Solution Approach 2:
The invention changes the electrical connection parameters of bottom electrodes from a fixed configuration to a variable configuration. By adjusting the connection ratio and configuration of bottom electrodes, the input capacitance can be controlled even with high cell density, thereby maintaining fast turn on and off speeds while achieving low specific-on resistance
Data Source
AI summary
A semiconductor power device includes a plurality of power transistor cells each having a trenched gate disposed in a gate trench opened in a semiconductor substrate wherein a plurality of the trenched gates further include a shielded bottom electrode disposed in a bottom portion of the gate trench electrically insulated from a top gate electrode disposed at a top portion of the gate trench by an inter-electrode insulation layer. At least one of the shielded bottom electrode is connected a source metal and at least one of the top electrodes in the gate trench is connected to a source metal of the power device.