Lateral MOSFET Gate Protection for SiC Power Devices
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Solution Overview
Problem
Wide bandgap semiconductor devices, such as SiC-MOSFETs, face challenges with poly-Zener diodes being less controllable in high temperature environments, making them unsuitable for applications requiring effective electrostatic discharge protection.
Innovation Solution
Incorporating a lateral MOSFET of a p-channel type connected between the gate and source of a SiC-MOSFET, where the control electrodes of both MOSFETs are common, allowing main currents to flow perpendicular and parallel to the substrate surface, effectively redirecting gate current to prevent overvoltage damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate area of SiC-MOSFET is reduced to decrease capacitance, then the ESD tolerance between gate and source deteriorates
Solution Approach 1:
A lateral MOSFET is introduced as an intermediary protective element connected between the gate and source of the vertical SiC-MOSFET. This lateral MOSFET acts as a mediator that diverts electrostatic discharge current away from the gate-source junction, protecting the main device while allowing the gate area to remain small for low capacitance operation.
Solution Approach 2:
The protection function is segmented from the main vertical MOSFET structure by adding a separate lateral MOSFET. The vertical MOSFET handles the main power switching function with minimized gate area, while the lateral MOSFET specifically handles ESD protection, allowing each component to be optimized independently.
2Reliability
If poly-Zener diodes are used for ESD protection, then electrostatic discharge damage is prevented, but temperature control capability deteriorates in high temperature environments
Solution Approach 1:
The invention changes the protective element from a poly-Zener diode to a lateral MOSFET, fundamentally altering the protection mechanism. The lateral MOSFET uses field-effect control with a gate threshold voltage that remains stable at high temperatures, unlike Zener diodes whose breakdown voltage drifts with temperature. This parameter change enables reliable ESD protection while maintaining temperature control capability in high temperature environments.
Data Source
AI summary
A semiconductor device includes a first MOS transistor and a second MOS transistor of a second conductivity type. The first MOS transistor includes a first main electrode connected to a first potential and a second main electrode connected to a second potential. The second MOS transistor includes a first main electrode connected to a control electrode of the first MOS transistor and a second main electrode connected to the second potential. The control electrodes of the first and second MOS transistors are connected in common. The first and second MOS transistors are formed on a common wide bandgap semiconductor substrate. In the first MOS transistor, a main current flows in a direction perpendicular to a main surface of the wide bandgap semiconductor substrate. In the second MOS transistor, a main current flows in a direction parallel to the main surface of the wide bandgap semiconductor substrate.