MOSFET and Schottky Diode Layout to Suppress PN Junction Conduction
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Solution Overview
Problem
In electronic circuits using MOSFETs, the flow of electric current through PN junction diodes can lead to device deterioration due to recombination of electrons and holes at crystal defects, particularly in SiC MOSFETs, causing forward direction deterioration and increased on-resistance.
Innovation Solution
An electronic circuit design that includes a bipolar device and a unipolar device connected in parallel, with an output line connected to both, where the inductance between the unipolar device and the output line is smaller than between the bipolar device and the output line, preventing current flow through the bipolar device by generating a counter electromotive force that does not exceed its operating voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Schottky barrier diode is connected in parallel to the PN junction diode to prevent current flow through the PN junction diode, then the forward direction deterioration is prevented, but a counter electromotive force is generated by parasitic inductance that can cause current to flow through the PN junction diode
Solution Approach 1:
The patent changes the inductance parameter of the current path by reducing the loop area and optimizing the layout of conductors. Specifically, the source electrode and anode electrode are connected through a minimized path, and the inductance is reduced to ensure the counter electromotive force does not exceed the forward voltage of the PN junction diode, preventing harmful current flow.
Solution Approach 2:
The patent applies preliminary anti-action by designing the current path with minimized inductance from the outset, so that the counter electromotive force generated during operation is inherently limited. The layout is configured beforehand to ensure that even when current flows through the Schottky barrier diode, the resulting counter electromotive force remains below the threshold that would cause PN junction diode conduction.
2Reliability
If the inductance between the unipolar device and output line is reduced to prevent current flow through the bipolar device, then the device performance is maintained, but the circuit design complexity increases
Solution Approach 1:
The patent merges the Schottky barrier diode and PN junction diode into a single integrated structure where they share common electrodes (source electrode and drain electrode). This integration reduces design complexity compared to separate discrete components, while the minimized current path layout simultaneously achieves the required low inductance for preventing PN junction diode conduction.
Solution Approach 2:
The patent applies local quality by optimizing specific regions of the device structure. The current path between the source electrode and anode electrode is locally minimized in loop area, while other parts of the device maintain standard configurations. This localized optimization achieves low inductance without requiring complete redesign of the entire circuit.
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 design effectively restrains current flow through the PN junction diode, preventing crystal defect area expansion and maintaining device performance by ensuring the counter electromotive force does not exceed the bipolar device's forward voltage, thus preventing forward direction deterioration of the MOSFET.
Implementation Method 1
a phenomenon in which an electric current flows through a PN junction diode has occurred. The inventor of the present application has discovered that this phenomenon is caused by a parasitic inductance of a current path passing through the Schottky barrier diode. In other words, when an electric current starts flowing through the Schottky barrier diode, a counter electromotive force is generated by a parasitic inductance of a current path passing through the Schottky barrier diode.
Data Source
AI summary
A semiconductor device includes a MOSFET including a PN junction diode. A unipolar device is connected in parallel to the MOSFET and has two terminals. A first wire connects the PN junction diode to one of the two terminals of the unipolar device. A second wire connects the one of the two terminals of the unipolar device to an output line, so that the output line is connected to the MOSFET and the unipolar device via the first wire and the second wire. In one embodiment the connection of the first wire to the diode is with its anode, and in another the connection is with the cathode.