MOSFET Super Junction Charge Balance for Switching Loss Reduction
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Solution Overview
Problem
Conventional MOSFETs experience irregularities in switching characteristics when turned off due to charge balance irregularities around the gate, leading to increased switching losses and potential defects in power conversion circuits.
Innovation Solution
A MOSFET with a super junction structure featuring n-type and p-type column regions, where the average positive charge density is expressed by an upward convex curve, ensuring a small deviation in charge balance even when the MOSFET becomes n-type dopant rich, minimizing the electric field near the gate and reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the total amount of dopant in the n-type column region is set equal to the total amount of dopant in the p-type column region, then the MOSFET achieves low ON resistance and high withstand voltage, but irregularities in charge balance around the gate cause irregularities in switching characteristics when the MOSFET is turned off
Solution Approach 1:
The patent applies local quality by making the dopant concentration distribution non-uniform within the n-type column region. Specifically, the dopant concentration is set to be higher near the gate and lower toward the bottom, creating different local characteristics that collectively improve the overall charge balance around the gate while maintaining low ON resistance and high withstand voltage.
Solution Approach 2:
The patent changes the dopant concentration parameter from a uniform distribution to a non-uniform distribution in the n-type column region. By controlling the dopant concentration to decrease from the gate side toward the bottom, the patent optimizes the charge balance around the gate, thereby improving switching characteristics and reducing switching losses.
2Reliability
If the dopant concentration in the n-type column region is increased to reduce ON resistance, then the ON resistance decreases, but the charge balance around the gate becomes irregular causing switching characteristic irregularities
Solution Approach 1:
The patent applies local quality by creating different dopant concentration levels in different regions of the n-type column region. The higher concentration near the gate reduces ON resistance, while the lower concentration toward the bottom helps maintain charge balance, thus resolving the contradiction between resistance reduction and switching characteristic stability.
Solution Approach 2:
The patent segments the n-type column region into different zones with different dopant concentrations. By dividing the region and assigning different dopant levels to different segments, the patent achieves both low ON resistance (in the gate-proximal segment) and stable switching characteristics (in the overall structure).
Data Source
AI summary
A MOSFET according to the present invention includes a semiconductor base substrate having a super junction structure. A gate electrode is on a first main surface side of the semiconductor base substrate by way of a gate insulation film, wherein in a state where a total amount of dopant in an n-type column region differs from a total amount of dopant in a p-type column region, assuming a depth position where an average positive charge density ρ(x) becomes 0 as Xm′, assuming a deepest depth position of the surface of the depletion layer on the first main surface side as X0′, assuming a depth position where the reference average positive charge density ρ0(x) becomes 0 as Xm, and assuming a deepest depth position of the depletion layer on the first main surface side as X0, a relationship of |X0−X0′|<|Xm−Xm′| is satisfied.