SiC MOSFET Parasitic Diode Isolation for Crystal Defect Prevention
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Solution Overview
Problem
Conventional semiconductor devices using silicon carbide (SiC) MOSFETs in inverter applications experience crystal defects due to transient currents flowing through parasitic diodes during switching operations, leading to reduced performance and reliability.
Innovation Solution
A semiconductor device structure is designed with a trench-gate field effect transistor configuration on a wide-bandgap semiconductor substrate, where the parasitic diode is isolated from the electrode pad, ensuring that transient currents flow through external Schottky barrier diodes instead of parasitic diodes, preventing minority carrier recombination and subsequent crystal defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If SiC MOSFETs are used in inverter applications with conventional structures, then high switching speed and current handling capability are achieved, but crystal defects occur due to transient currents flowing through parasitic diodes during switching operations
Solution Approach 1:
The invention extracts the problematic parasitic diode function from the MOSFET structure by isolating the electrode pad from the parasitic diode region. This is achieved by forming an insulating film between the electrode pad and the parasitic diode, effectively removing the harmful current path while preserving the useful switching function of the MOSFET.
Solution Approach 2:
The invention segments the device structure into distinct functional regions: a transistor region containing the MOSFET and a pad region containing the electrode pad, separated by an insulating film. This segmentation prevents transient currents from flowing through the parasitic diode during switching operations, eliminating crystal defect formation while maintaining high switching speed performance.
2Adaptability or versatility
If parasitic diodes are present in conventional MOSFET structures, then freewheeling diode function is provided, but transient currents cause minority carrier recombination and crystal defects
Solution Approach 1:
The invention introduces an insulating film as an intermediary element between the electrode pad and the parasitic diode. This intermediary structure allows the parasitic diode to maintain its freewheeling diode function while preventing transient switching currents from flowing through it, thereby eliminating minority carrier recombination and crystal defect formation.
Solution Approach 2:
By segmenting the device into transistor and pad regions separated by an insulating film, the invention enables the parasitic diode to function as a freewheeling diode during normal operation while preventing harmful transient current flow during switching operations, thus maintaining versatility without compromising reliability.
3Device complexity
If electrode pad is directly connected to parasitic diode in conventional structures, then simple structure is maintained, but transient currents cannot be directed away from parasitic diodes
Solution Approach 1:
The invention extracts the electrode pad from direct electrical connection to the parasitic diode by introducing an insulating film. This modification adds minimal structural complexity while effectively directing transient currents away from the parasitic diode, preventing crystal defect formation without significantly complicating the device structure.
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 configuration increases the forward voltage applied to parasitic diodes, directing transient currents through external diodes and preventing crystal defects, thereby enhancing the reliability and performance of SiC MOSFETs in inverter applications.
Implementation Method 1
wide-bandgap semiconductors can also be used to make (manufacture) Schottky barrier diodes (SBDs). For these reasons, using a wide-bandgap semiconductor as a substrate material makes it possible to create SBDs with high breakdown voltage and low on-resistance.
Implementation Method 2
MOSFETs have a built-in parasitic diode formed by the p-n junction between a p-type base region and an n− drift region.
Data Source
AI summary
In a transistor region of an active region, trench-gate MOS gates for a vertical MOSFET are formed on the front surface side of a semiconductor substrate. In a non-effective/pad region of the active region, a gate pad is formed on the front surface of the semiconductor substrate with an interlayer insulating film interposed therebetween. An n-type region is formed spanning across the entire non-effective region in the surface layer of the front surface of the semiconductor substrate. The portion directly beneath the gate pad is only an n-type region constituted by an n+ starting substrate, an n− drift region, and the n-type region, with the interlayer insulating film sandwiched thereabove. No n+ source region is formed in a p-type base region extension which is the portion of a p-type base region that extends into the non-effective region.