Power IGBT Latch-Up Resistance via Cell Density Segmentation
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Solution Overview
Problem
Power IGBTs face the challenge of 'latch-up' during switching off, where high hole current density leads to parasitic npn bipolar transistor activation, potentially causing component destruction, especially in regions with reduced cell density and increased switching losses due to slow switching-off operations.
Innovation Solution
The power IGBT design incorporates a cell array with sections of varying cell densities, reduced emitter efficiency in low-density regions, and optionally increased field stop zone doping or reduced charge carrier lifetime to minimize hole current density and enhance 'latch-up' resistance, including modified transistor cells and increased contact areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the component is switched off rapidly, then switching losses are reduced, but a latch-up may occur due to high hole current density
Solution Approach 1:
The patent applies local quality by creating regions with different cell densities within the cell array. Specifically, it introduces first regions with a first cell density and second regions with a second cell density that is lower than the first cell density. This local variation in cell density allows different regions to have different hole current densities during switching off, enabling rapid switching in high-density regions while maintaining latch-up resistance in low-density regions.
2Reliability
If the cell density is reduced in certain regions, then latch-up resistance is improved, but the area available for current conduction is reduced
Solution Approach 1:
The patent segments the cell array into multiple regions with different cell densities. The cell array is divided into first regions with higher cell density and second regions with lower cell density. This segmentation allows the device to optimize different areas for different functions: high-density regions for current conduction and low-density regions for latch-up resistance, thereby resolving the contradiction between area utilization and reliability.
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 reduces the risk of 'latch-up' and associated voltage or current limitations, while minimizing switching losses by managing hole current and charge carrier lifetime in critical regions, thereby enhancing the robustness and operational safety of the power IGBT.
Implementation Method 1
The emitter zone (11) has a lower emitter efficiency in a region corresponding to the second cell array section (102) than in a region corresponding to the first cell array section (101)
Implementation Method 2
The parasitic npn bipolar transistor switches on when the hole current flowing away from the drift zone (12) when the component is being switched off is so high that the voltage drop caused by this hole current under the source zones (15) in the body zone (14) is greater than the threshold voltage of the parasitic bipolar transistor
Implementation Method 3
When the IGBT is on, the drift zone (12) is flooded with p-type charge carriers or holes which, when the power IGBT is being switched off, must flow away
Data Source
AI summary
A power IGBT includes a semiconductor body having an emitter zone of a first conduction type and a drift zone of a second conduction type proximate to the emitter zone. The IGBT further includes a cell array, each transistor cell of the array having a source zone, a body zone disposed between the source zone and the drift zone, the body zone and source zone short-circuited, and a gate electrode configured to be insulated with respect to the source zone and the body zone. The cell array has a first cell array section with a first cell density and a second cell array section with a second cell density that is lower than the first cell density. The emitter zone has a lower emitter efficiency in a region corresponding to the second cell array section than in a region corresponding to the first cell array section.