Vertical Power MOSFET Super Junction Ringing Suppression
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Solution Overview
Problem
Vertical power MOSFETs with super junction structures face the challenge of ringing due to high-speed switching, which compromises their performance by inducing voltage spikes during turn-off operations.
Innovation Solution
Incorporating an undergate heavily doped N-type region with a shallower depth and higher concentration than the drift region, positioned between body regions, to increase gate-drain capacitance and mitigate ringing without compromising switching speed or withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-speed switching is implemented in vertical power MOSFET with super junction, then switching speed is improved, but ringing and voltage spikes occur during turn-off
Solution Approach 1:
The patent introduces a lightly doped N-type region positioned between the P-type body region and the N-type drift region, which preliminarily establishes a charge distribution that reduces electric field concentration before turn-off occurs. This preliminary charge arrangement suppresses ringing and voltage spikes during the switching transition without compromising switching speed.
Solution Approach 2:
The patent applies local quality by creating a specifically doped region with tailored impurity concentration (lightly doped, between the body and drift regions) at a specific location (between P-type body and N-type drift regions). This localized modification addresses the ringing problem only where needed, preserving high-speed switching characteristics in other regions.
2Reliability
If N-type column region concentration is increased to secure charge balance, then charge balance is improved, but electric field concentration increases at the lower end portion
Solution Approach 1:
The patent segments the N-type column region into two distinct parts: an upper half portion with relatively higher concentration and a lower half portion with relatively lower concentration. This segmentation allows the upper portion to contribute to charge balance while the lower portion reduces electric field concentration at critical interfaces.
Solution Approach 2:
The patent applies different concentration levels to different portions of the N-type column region. The upper half has higher concentration for charge balance, while the lower half has lower concentration to reduce electric field stress. This local quality variation resolves the contradiction between charge balance and electric field concentration.
3Object-generated harmful factors
If undergate heavily doped N-type region is introduced to suppress ringing, then ringing suppression is improved, but device complexity increases
Solution Approach 1:
The patent changes the doping concentration parameter in a specific region (lightly doped N-type region between body and drift regions) to suppress ringing. By adjusting only the concentration parameter rather than adding entirely new structural elements, the solution achieves ringing suppression with minimal increase in device complexity.
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 suppresses ringing while maintaining high-speed switching characteristics and ensuring reliable operation by enhancing gate-drain capacitance at the onset of depletion, thus preventing voltage spikes and maintaining performance.
Implementation Method 1
Incorporating an undergate heavily doped N-type region with a shallower depth and higher concentration than the drift region, positioned between body regions, to increase gate-drain capacitance and mitigate ringing
Data Source
AI summary
Vertical power MOSFETs having a super junction are devices capable of having a lower on resistance than other vertical power MOSFETs. Although they have the advantage of high-speed switching due to rapid depletion of an N type drift region at the time of turn off in switching operation, they are likely to cause ringing. A vertical power MOSFET having a super junction structure provided by the present invention has, in the surface region of a first conductivity type drift region under a gate electrode, an undergate heavily doped N type region having a depth shallower than that of a second conductivity type body region and having a concentration higher than that of the first conductivity type drift region.