Trench Gate Width Variation Reduces IGBT Switching Loss
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Solution Overview
Problem
Conventional IGBTs with expanded lower portions of trench gate structures face increased gate capacitance, leading to slower switching speed and higher switching losses, as well as difficulties in controlling the rise and fall times of collector current due to large gate capacitance.
Innovation Solution
The semiconductor device features a trench structure with varying widths and depths, including a first trench portion, a second trench portion connected to the first, and a third trench portion along the side wall of the second trench portion, with a gate insulating film thickness that differs between these regions, optimizing the trench geometry to reduce gate capacitance and enhance switching performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lower portion of the trench gate structure is expanded, then the ON voltage decreases due to hole accumulation and injection enhancement effect, but the gate capacitance increases leading to slower switching speed and higher switching losses
Solution Approach 1:
The patent applies local quality by creating different trench width regions: a first region with a first width and a second region with a second width greater than the first width. This allows the lower portion of the trench to be locally expanded to enhance hole accumulation and injection enhancement effect for reducing ON voltage, while the upper portion maintains a narrower width to limit gate capacitance increase and reduce switching losses.
Solution Approach 2:
The trench gate structure is segmented into multiple regions with different widths. The trench is divided into a first region extending from the semiconductor surface to a first depth, and a second region extending from the first depth to a second depth greater than the first depth. This segmentation allows independent optimization of each region's contribution to device performance.
2Reliability
If the lower portion of the trench gate structure is expanded, then the injection enhancement effect is enhanced, but the rise and fall times of collector current become difficult to control due to large gate capacitance
Solution Approach 1:
By implementing local expansion only in the second region (lower portion) while maintaining the first region (upper portion) with a narrower width, the patent achieves enhanced injection enhancement effect for improved switching capability while controlling the overall gate capacitance to maintain controllability of rise and fall times.
3Reliability
If the trench width is increased in the lower portion, then the accumulation layer thickness is optimized for hole accumulation, but the gate capacitance increases
Solution Approach 1:
The patent implements local quality by having the trench width vary along the depth: narrower in the upper first region and wider in the lower second region. This allows the accumulation layer to be optimized for hole accumulation in the lower portion while the upper portion's narrower width helps control the overall gate capacitance.
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 configuration effectively reduces ON voltage and switching loss while improving switching capability by controlling the accumulation layer thickness and hole injection, thereby enhancing the injection enhancement effect and reducing latch-up occurrences.
Implementation Method 1
a gate insulating film disposed on an inner wall of the trench... A width of the second trench portion is wider than a width of the first trench portion, and a width of the third trench portion and a width of the fourth trench portion respectively differ.
Implementation Method 2
suppresses the amount of holes drawn from the p-type contact layer 58 through the p-type base layer 54 disposed on the n-type drift layer 53 and causes holes to accumulate in the n-type drift layer 53, which is an upper portion connected to the channel.
Implementation Method 3
the amount of electrons attracted by the accumulated holes and injected into the n-type drift layer 53 through the channel increase, whereby the ON voltage decreases. Increasing the amount of electrons injected from the channel by an accumulation of holes in this manner is called the injection enhancement (IE) effect.
Data Source
AI summary
In a trench deeper than a thickness of a p-type base layer and configured by a first trench and a second trench, a second trench positioned at a lower portion is configured by a third trench and a fourth trench. A width of the second trench along an X direction is expanded more than the first trench positioned above the second trench. Along the X direction, the extent to which the second trench is expanded differs for the third trench and the fourth trench. Thus, a width of the lower portion of the trench differs along a Y direction, enabling reduced gate capacitance compared to uniform expansion along a transverse direction of the trench. Further, ON voltage may be reduced and switching capability may be improved.