IGCT Lateral Resistance Reduction via Edge Doping
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Solution Overview
Problem
Integrated gate commutated thyristors (IGCTs) face latch-up issues during high voltage and current turn-off due to the distribution of peak electric fields and hole flow, leading to re-latching and device failure.
Innovation Solution
A four-layer power semiconductor device with a resistance reduction layer of higher doping concentration than the base layer, positioned between the cathode layer and the base layer, reduces lateral resistance and prevents re-latching by effectively collecting holes, enhancing immunity to latch-up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a highly doped base layer is used to reduce resistance, then electrical conductivity is improved, but hole accumulation at the cathode layer edge increases causing re-latching
Solution Approach 1:
The patent applies local quality by creating a laterally non-uniform doping distribution in the base layer. Specifically, the base layer has a first doping concentration in the central region and a second, lower doping concentration at the lateral edges. This local variation allows the central region to provide low resistance while the edge regions prevent hole accumulation, thus resolving the contradiction between conductivity and latch-up immunity.
Solution Approach 2:
The base layer is segmented into different doping regions - a highly doped central region and a less doped edge region. This segmentation allows each region to perform its specific function: the central region provides electrical conductivity while the edge region prevents hole accumulation, thereby solving the contradiction.
2Productivity
If the cathode layer width is increased to improve current handling, then current capacity is improved, but the distance holes must travel increases leading to higher re-latching risk
Solution Approach 1:
The patent reduces lateral resistance specifically at the edge regions where holes accumulate, without reducing the overall cathode layer width. The base layer has elevated doping concentration at the lateral edges, which locally reduces resistance for hole collection while maintaining the necessary current handling capacity of the full device.
3Ease of manufacture
If uniform doping is used in the base layer for simplicity, then manufacturing complexity is reduced, but edge effects cause device failure
Solution Approach 1:
The patent implements local quality through a laterally non-uniform doping profile in the base layer, with different doping concentrations in the central region versus the edge regions. This requires more complex manufacturing than uniform doping but is achieved through controlled diffusion or implantation processes that create the desired gradient, ensuring device stability by preventing edge-related failures.
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 solution effectively reduces the risk of latch-up during turn-off, maintaining device performance and preventing re-latching, thereby increasing the safe operating area and reliability of the IGCT.
Implementation Method 1
A resistance reduction layer of a second conductivity type and having a higher doping concentration than the base layer is arranged between the base layer and the cathode layer on the cathode side
Implementation Method 2
During high stress such as high voltage and high current turn-off switching, the device enters dynamic avalanche whereas the peak electric field is distributed uniformly in the active region along the whole main blocking junction between the cathode layer 5 and the base layer 6
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
A power semiconductor device includes a four-layer structure having layers arranged in order: (i) a cathode layer of a first conductivity type with a central area being surrounded by a lateral edge, the cathode layer being in direct electrical contact with a cathode electrode, (ii) a base layer of a second conductivity type, (iii) a drift layer of the first conductivity typehaving a lower doping concentration than the cathode layer, and (iv) an anode layer of the second conductivity type which is in electrical contact with an anode electrode. The base layer includes a first layer as a continuous layer contacting the central area of the cathode layer. A resistance reduction layer, in which the resistance at the junction between the lateral edge of the cathode and base layers is reduced, is arranged between the first layer and the cathode layer and covers the lateral edge of the cathode layer.