IGBT Edge Structures for Uniform Current Flow
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Insulated gate turn-off thyristors (IGTOs) experience a decrease in breakover voltage due to edge cells, leading to premature turn-on and non-uniform current flow, which is undesirable as it is not solely controlled by the gate voltage.
Innovation Solution
The implementation of a two-dimensional array of cells with inner and edge cells, where the edge cells have a reduced n+ dopant concentration profile and deep insulating trenches to prevent hole injection, ensuring uniform current flow and maintaining breakover voltage similar to inner cells, and the use of p+ areas for shorting to reduce thermal runaway.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If edge cells are designed with the same structure as inner cells, then manufacturing is simplified, but breakover voltage decreases and current flow becomes non-uniform
Solution Approach 1:
The patent applies local quality by making edge cells structurally different from inner cells. Specifically, edge cells have reduced n+ dopant concentration in the emitter region compared to inner cells. This local modification compensates for the edge effect where holes accumulate at the periphery, preventing premature turn-on and ensuring uniform breakover voltage across the entire thyristor structure.
2Reliability
If edge cells have reduced n+ dopant concentration, then breakover voltage is maintained, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements parameter changes by systematically varying the n+ dopant concentration based on cell position. Edge cells are designed with lower n+ dopant concentration than inner cells. This parameter modification is integrated into the manufacturing process through controlled doping steps, where the dopant concentration profile is adjusted according to the spatial location, thereby maintaining breakover voltage uniformity while establishing clear manufacturing specifications.
3Reliability
If deep insulating trenches are added to prevent hole injection, then current flow uniformity improves, but device complexity increases
Solution Approach 1:
The patent applies segmentation by introducing deep insulating trenches that divide the device structure into distinct regions. These trenches extend from the surface to the substrate and are filled with insulating material, creating isolated regions that prevent hole accumulation and injection at the periphery. This segmentation approach effectively controls current flow distribution while maintaining a systematic structure that integrates with the overall device architecture.
4Reliability
If p+ areas are added for shorting, then thermal runaway is prevented, but manufacturing steps increase
Solution Approach 1:
The patent merges multiple functions into the p+ areas formed during manufacturing. These heavily doped p+ regions serve dual purposes: they provide low-resistance electrical contacts for current extraction and act as shorting paths that prevent thermal runaway by providing alternative current routes. By combining these functions into a single structural element formed during the doping process, the patent reduces the need for separate manufacturing steps while achieving both electrical and thermal management objectives.
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 solution achieves uniform current flow across the thyristor area, preventing thermal runaway and ensuring breakover voltage is maintained, allowing for controlled turn-on and off by the gate voltage.
Implementation Method 1
When the gate is forward biased, electrons from the n+ layer 18 become the majority carriers along the sidewalls and below the bottom of the trenches 24 in an inversion layer, causing the effective width of the NPN base (the portion of the p-well 16 below the trenches 24) to be reduced.
Implementation Method 2
the n+ layer 40 has a reduced dopant concentration profile next to the rightmost gate region 38A
Data Source
AI summary
An insulated gate turn-off thyristor, formed as a die, has a layered structure including a p+ layer (e.g., a substrate), an n− layer, a p-well, vertical insulated gate regions formed in the p-well, and n+ regions between the gate regions, so that vertical NPN and PNP transistors are formed. The thyristor is formed of a matrix of cells. Due to the discontinuity along the edge cells, a relatively large number of holes are injected into the n− epi layer and drift into the edge p-well, normally creating a higher current along the edge and lowering the breakover voltage of the thyristor. To counter this effect, the dopant concentration of the n+ region(s) near the edge is reduced to reduce the NPN transistor beta and current along the edge, thus increasing the breakover voltage. Alternatively, a deep trench may circumscribe the edge cells to provide isolation from the injected holes.