Reverse Conducting IGBT Lattice Design for Snapback Control
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Solution Overview
Problem
In reverse conducting IGBTs, the distribution density of dot-shaped diode cathode regions affects the forward voltage drop and snapback occurrence, making it difficult to control device characteristics and variations.
Innovation Solution
The dot-shaped diode cathode regions are distributed in a uniform XY lattice on the device chip, with a longer lattice constant in the Y direction than in the X direction, parallel to the linear gate electrodes, to achieve optimal fly-back diode characteristics and prevent snapback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the distribution density of diode cathode regions is increased, then the forward voltage drop of the fly-back diode is reduced, but snapback occurs and the PN junction at the collector part cannot turn ON properly
Solution Approach 1:
The patent applies local quality by creating regions with different diode cathode densities: a first region with a first density and a second region with a second density. This allows different areas of the device to have optimized characteristics - some areas prioritize low forward voltage drop while others prevent snapback, resolving the contradiction between these two opposing requirements.
Solution Approach 2:
The patent segments the diode cathode region into multiple zones with different distribution densities. By dividing the uniform structure into non-uniform segments with varying densities, the device can simultaneously achieve low forward voltage drop in high-density regions and snapback prevention in low-density regions.
2Reliability
If macro area diode cathode absent regions are provided, then snapback is avoided, but the arrangement directly affects device characteristics and variations become difficult to control
Solution Approach 1:
The patent changes the parameter of diode cathode density from a single macro-scale absent region to a controlled gradient or patterned distribution at the micro-scale. By adjusting the density parameter locally rather than creating large absent regions, the device maintains predictable characteristics while preventing snapback.
Data Source
AI summary
In a reverse conducting IGBT, diode cathode regions are formed dispersedly on the back side of a device chip. When the distribution density of the diode cathode region becomes low, VF of a fly-back diode, that is, a forward voltage drop becomes large. On the other hand, when the distribution density of the diode cathode region becomes high, it becomes hard for a PN junction at a collector part to turn ON and a snap back occurs. In contrast to this, there is a method of providing about one to several diode cathode absent regions having a macro area, however, the arrangement of the regions itself directly affects the device characteristics, and therefore, it is difficult to control the device characteristics and variations thereof.In the present invention, dot-shaped diode cathode regions on the back side of the device chip are distributed into the shape of a substantially uniform XY lattice and at the same time, the lattice constant in a Y direction is made longer than that in an X direction in parallel with a linear gate electrode in a reverse conducting IGBT having a large number of the linear gate electrodes.