SiC MOSFET Bipolar Current Suppression via Well Region Design
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Solution Overview
Problem
Silicon carbide semiconductor devices face reliability issues due to the passage of bipolar current through parasitic p-n diodes, leading to increased forward voltage and potential element breakdown, particularly in wide-bandgap semiconductor devices like silicon carbide, which can result in leakage currents and dielectric breakdown during switching operations.
Innovation Solution
A silicon carbide semiconductor device structure is designed with a semiconductor substrate, drift layer, well regions, separation regions, Schottky electrodes, and a thicker insulating film to suppress bipolar current flow and prevent element breakdown, featuring a non-ohmic connection between the source electrode and the second well region, and a conductive layer with low resistance to manage displacement currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bipolar current is passed through parasitic p-n diodes in silicon carbide semiconductor devices, then current flow is enabled, but stacking faults expand causing forward voltage to increase and reliability to deteriorate
Solution Approach 1:
The patent extracts and removes the parasitic p-n diode structure from the semiconductor device by eliminating the p-type well region that forms the parasitic diode with the n-type drift layer. This prevents bipolar current flow through the parasitic diode and eliminates the harmful stacking fault expansion while maintaining the desired unipolar MOSFET operation.
Solution Approach 2:
The patent converts the potentially harmful parasitic p-n diode structure into a beneficial configuration by redesigning the well region structure. The p-type well region is reconfigured to form a pn junction that does not create a forward-biased parasitic diode during normal operation, thereby eliminating the reliability issue while maintaining the structural benefits of the well region.
2Measurement precision
If forward current is passed through parasitic p-n diodes for reliability screening, then defective items can be identified, but the duration of current passage is prolonged and many defective items are produced
Solution Approach 1:
The patent eliminates the need for prolonged forward current screening by removing the parasitic p-n diode structure that causes the screening problem. Without the parasitic diode, the device can be screened using standard, shorter-duration methods without producing excessive defective items, as the underlying cause of forward voltage shifts during screening is eliminated.
3Reliability
If unipolar diodes are incorporated into MOSFET units to prevent bipolar current flow, then characteristics degradation is suppressed, but device structure becomes more complex
Solution Approach 1:
The patent makes the p-type well region serve multiple functions: it provides the standard well function for MOSFET operation and simultaneously forms a pn junction that prevents forward-biased parasitic diode conduction. This multi-functionality eliminates the need for separate unipolar diode structures while maintaining characteristic stability during free-wheeling operation.
Solution Approach 2:
The patent merges the function of preventing bipolar current flow with the existing p-type well region structure. By configuring the well region to form a pn junction with the n-type drift layer, the same structure that defines the MOSFET active region also prevents harmful parasitic diode operation, eliminating the need for additional unipolar diode components.
4Ease of operation
If terminal well regions are designed to protrude toward the periphery, then terminal access is improved, but parasitic p-n diodes form in these regions causing breakdown voltage reduction
Solution Approach 1:
The patent applies different structural characteristics to different regions: the terminal well regions protrude toward the periphery to provide good terminal access, but the impurity concentration and geometric configuration are locally optimized to prevent parasitic diode formation. This local quality adjustment maintains terminal accessibility while preventing breakdown voltage reduction in the terminal regions.
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
The proposed structure effectively suppresses element breakdown and enhances the reliability of silicon carbide semiconductor devices by reducing bipolar current flow and managing displacement currents, thereby improving the device's operational stability and efficiency.
Implementation Method 1
a plurality of first Schottky electrodes 71 forming Schottky junctions with the first separation regions 21
Implementation Method 2
the second insulating film 52 is thicker than the gate insulating film 50... the second insulating film 52 prevents discharge
Implementation Method 3
a non-ohmic connection between the source electrode and the second well region
Data Source
AI summary
In SiC-MOSFETs including Schottky diodes, passage of a bipolar current to a well region in a terminal region cannot be sufficiently reduced, which may reduce the reliability of elements. A SiC-MOSFET including Schottky diodes includes a gate electrode formed, through a second insulating film thicker than a gate insulating film in an active region, on a separation region between a first well region in the active region that is the closest to the terminal region and a second well region in the terminal region, wherein the second well region has a non-ohmic connection to a source electrode. Thus, a decrease in the reliability of elements is prevented.