MOSFET Super Junction Asymmetric Dopant Control for Surge Voltage Reduction
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Solution Overview
Problem
Conventional MOSFETs used in power conversion circuits face challenges with increased surge voltage when turned off, making it difficult to meet standard surge voltage requirements and resulting in high turn-off losses.
Innovation Solution
A MOSFET with a semiconductor base substrate featuring a super junction structure of n-type and p-type column regions, where the total dopant amount in the p-type column region is set between 1.00 to 1.03 times that of the n-type column region, allowing for controlled drain current phases during turn-off, reducing surge voltage and turn-off loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional MOSFET with balanced n-type and p-type column regions is used, then the MOSFET achieves low ON resistance and high withstand voltage, but the surge voltage increases when turned off
Solution Approach 1:
The patent applies asymmetry by intentionally making the total dopant amount in the p-type column region (1.00 to 1.03 times) slightly different from the n-type column region, breaking the conventional balanced structure. This asymmetric dopant distribution creates a controlled charge imbalance that extends the turn-off current period and reduces the drain current gradient, thereby suppressing surge voltage while maintaining high withstand voltage capability
2Speed
If the MOSFET turn-off time is reduced, then the switching speed improves, but the turn-off loss increases
Solution Approach 1:
The patent changes the dopant concentration parameter in the p-type column region to a specific range (1.00 to 1.03 times the n-type dopant amount). This parameter modification extends the turn-off current period by controlling the charge depletion characteristics, which reduces the drain current gradient and consequently lowers turn-off loss while maintaining acceptable switching speed
3Object-affected harmful factors
If the drain current gradient is reduced, then the surge voltage decreases, but the turn-off time increases
Solution Approach 1:
The patent applies local quality by creating a specific dopant distribution pattern in the p-type column region that is localized to the super junction structure. This localized dopant adjustment (1.00 to 1.03 times the n-type amount) specifically affects the charge depletion characteristics during turn-off, extending the current period and reducing the gradient without significantly impacting overall turn-off time
Data Source
AI summary
A MOSFET includes a semiconductor base substrate where a super junction structure is formed of an n-type column region and a p-type column region. A total amount of a dopant in the n-type column region is set to a value greater than a total amount of a dopant in the p-type column region. The MOSFET is configured to be operated during a period from a point of time when a drain current starts to decrease to a point of time when the drain current becomes 0 for the first time in response to turning off of the MOSFET such that a first period during which the drain current is decreased, a second period during which the drain current is increased or the drain current becomes constant, and a third period during which the drain current is decreased again occur in this order.