Transistor Second Body Region for Avalanche Robustness
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Solution Overview
Problem
Transistor devices for power applications face challenges in avalanche robustness due to localized electric fields and uneven current distribution, leading to potential overheating and device failure.
Innovation Solution
Incorporating a second body region with a higher doping concentration laterally adjacent and overlapping with the source contact, which increases the avalanche failure current and improves robustness by redistributing the peak of impact ionization away from the source contact end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional transistor device structure is used, then the device is simple to manufacture, but the avalanche robustness is poor due to localized electric fields and uneven current distribution
Solution Approach 1:
The patent introduces a second body region with higher doping concentration specifically positioned adjacent to the source contact, creating a localized modification rather than changing the entire device structure. This local quality enhancement targets the specific area where avalanche breakdown initiates, improving robustness without complicating the overall device architecture
Solution Approach 2:
The patent modifies the doping concentration parameter by introducing a second body region with higher doping concentration than the first body region. This parameter change alters the electric field distribution and impact ionization characteristics, thereby improving avalanche robustness while maintaining compatibility with existing manufacturing processes
2Reliability
If the avalanche breakdown occurs over a large area, then the avalanche current density is reduced, but the peak lateral electric field at edges causes preferential breakdown at edge locations
Solution Approach 1:
The second body region is strategically positioned adjacent to the source contact where the peak lateral electric field occurs, creating a localized modification that specifically addresses the high-stress area. This allows the electric field to be redistributed away from the edge, preventing preferential breakdown while maintaining effective avalanche current distribution
Solution Approach 2:
The second body region acts as an intermediary structure between the source contact and the drift region, mediating the electric field distribution. By introducing this intermediate doped region, the patent smooths out the discontinuities at the edge and redistributes the peak lateral electric field, preventing concentration at specific locations
3Reliability
If the critical temperature is reached in one specific area due to lower breakdown voltage, then the device fails in that area, but increasing avalanche current sharing among cells increases robustness
Solution Approach 1:
The second body region is positioned specifically adjacent to the source contact where impact ionization peaks, creating a localized modification that prevents thermal runaway in that critical area. This local enhancement ensures more uniform temperature distribution by preventing concentration of avalanche current in specific high-field regions
Solution Approach 2:
The second body region is pre-positioned to modify the electric field distribution before avalanche breakdown occurs. By having this higher-doped region in place beforehand, the patent prevents the formation of hot spots and ensures more uniform current distribution from the outset, rather than attempting to correct thermal issues after they arise
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 enhances avalanche robustness by increasing the avalanche failure current up to a factor of 2 without affecting other MOSFET electrical parameters, such as Rdson, Vth, and Qg, and does so with minimal additional process cost and no increase in RonA or reduction in active area.
Implementation Method 1
the peak of impact ionization is moved away from the first distal end of the elongate source contact and the avalanche robustness is improved
Data Source
AI summary
A transistor device includes a semiconductor substrate having a first major surface, a cell field including transistor cells, and an edge termination region laterally surrounding the cell field. Each transistor cell includes a drift region of a first conductivity type, a first body region of a second conductivity type on the drift region, a source region of the first conductivity type on the first body region and a gate electrode. The transistor device further includes an elongate source contact having opposing first and second distal ends, the elongate source contact being in contact with the source region, and a second body region of the second conductivity type positioned in the semiconductor substrate. The second body region has a lateral extent such that it is spaced part from the second distal end of the elongate source contact and extends laterally beyond the first distal end of the elongate source contact.