Super Junction MOSFET Defect Layout for Reverse Recovery Stability
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Solution Overview
Problem
MOSFETs with super junction structures experience large junction capacitance and rapid depletion layer expansion during reverse recovery, leading to rapid reverse recovery currents and potential oscillation due to crystal defects in the semiconductor base substrate.
Innovation Solution
A MOSFET design where crystal defects are selectively formed only in the active and active connecting regions of the semiconductor base substrate, with specific area and depth distributions to control carrier recoupling and reduce reverse recovery current peaks, thereby minimizing oscillation and recovery loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If crystal defects are formed in the semiconductor base substrate to control carrier lifetime and reduce reverse recovery charge, then reverse recovery loss is reduced, but oscillation is generated more easily due to rapid reverse recovery current decay
Solution Approach 1:
The patent applies local quality by creating different crystal defect distributions in different regions of the semiconductor base substrate. The active region has a first crystal defect density while the outer peripheral region has a second crystal defect density that is lower than the first. This spatial variation in defect quality allows the active region to provide adequate carrier recoupling for loss reduction while the outer peripheral region maintains smoother current characteristics to suppress oscillation.
2Speed
If the density of crystal defects is increased to further reduce reverse recovery time, then switching speed is improved, but the reverse recovery current becomes excessively rapid and oscillation is exacerbated
Solution Approach 1:
The patent implements local quality by establishing different crystal defect densities in different spatial regions. The active region contains sufficient crystal defects to enable rapid carrier recoupling and achieve fast switching speed, while the outer peripheral region has reduced crystal defect density to prevent excessive current decay rates that would cause oscillation. This localized differentiation resolves the contradiction between speed and oscillation suppression.
3Loss of energy
If crystal defects are uniformly distributed throughout the semiconductor base substrate, then carrier recoupling is enhanced and reverse recovery charge is reduced, but reverse recovery current becomes excessively rapid causing oscillation
Solution Approach 1:
The patent resolves this contradiction by abandoning uniform crystal defect distribution in favor of a spatially varying distribution. The active region maintains adequate crystal defect density for effective carrier recoupling and low reverse recovery charge, while the outer peripheral region has reduced crystal defect density to ensure gradual current decay and suppress oscillation. This local differentiation allows both objectives to be achieved simultaneously.
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 selective formation of crystal defects in the MOSFET reduces reverse recovery charge and oscillation, enhancing switching speed and reducing recovery loss by controlling carrier recoupling and delaying carrier extinction in the outer peripheral region.
Implementation Method 1
carriers can be recoupled at the crystal defects (a lifetime of carriers can be controlled) at the time of reverse recovery of a body diode
Implementation Method 2
a junction capacitance of the super junction structure is large and a depletion layer rapidly expands from a pn junction at the time of reverse recovery of a body diode
Data Source
AI summary
A MOSFET includes: a semiconductor base substrate having an n-type column region and a p-type column region, the n-type column region and the p-type column region forming a super junction structure; and a gate electrode formed by way of a gate insulation film. Assuming a region of the semiconductor base substrate which provides a main operation of the MOSFET as an active region, a region of the semiconductor base substrate maintaining a withstand voltage of the MOSFET as an outer peripheral region, and a region of the semiconductor base substrate disposed between the active region and the outer peripheral region as an active connecting region, out of the active region, the active connecting region, and the outer peripheral region of the semiconductor base substrate, the crystal defects are formed only in the active region and the active connecting region.