Double-Sided RC-IGBT Gate Structure for Current Concentration Control
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Solution Overview
Problem
In reverse-conducting insulated gate bipolar transistors (RC-IGBTs), the interference between the IGBT and freewheeling diode operations leads to deteriorated element characteristics, particularly due to current concentration at the end of the IGBT region, which can cause damage.
Innovation Solution
The implementation of a double-sided gate structure with a third transistor in the boundary region having a lower threshold voltage than the second transistor, which is connected to the second gate electrode, helps to suppress hole injection into the drift region, reducing current concentration and preventing damage during turn-off operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a boundary region is provided between the IGBT region and diode region, then the interference between IGBT and diode operations is suppressed, but holes injected from the back surface of the boundary region cause current concentration at the end of the IGBT region leading to potential damage
Solution Approach 1:
A third transistor is introduced as an intermediary component in the boundary region. This third transistor acts as a mediator that selectively extracts holes from the drift region near the boundary, preventing hole accumulation that would otherwise cause current concentration and damage to the IGBT structure.
Solution Approach 2:
The third transistor is designed with a lower threshold voltage than the second transistor, changing the electrical parameter of threshold voltage to enable the third transistor to activate first during turn-off operations. This parameter change allows precise control over when and how holes are extracted from the drift region.
2Area of stationary object
If the IGBT and freewheeling diode are formed in the same semiconductor chip, then chip size is reduced and heat generation locations are dispersed, but the operation of the IGBT and diode interfere with each other deteriorating element characteristics
Solution Approach 1:
The semiconductor chip is segmented into distinct functional regions: an IGBT region with first and second transistors, a diode region, and a boundary region containing a third transistor. This segmentation allows each region to operate independently with optimized characteristics while sharing the same chip substrate.
Solution Approach 2:
The third transistor in the boundary region serves as an intermediary that prevents harmful interactions between the IGBT and diode operations. By selectively managing hole injection and extraction at the boundary, it protects the IGBT region from interference caused by diode operation.
3Object-affected harmful factors
If a third transistor with lower threshold voltage is provided in the boundary region, then hole injection into the drift region is suppressed reducing current concentration, but device complexity increases
Solution Approach 1:
The third transistor performs multiple functions: it extracts holes from the drift region during turn-off to prevent current concentration, and its lower threshold voltage ensures it activates before the main transistors. This multi-functional design addresses several problems simultaneously without requiring additional external control circuits.
Solution Approach 2:
The invention adds a new dimensional aspect to the transistor structure by introducing a third transistor in the boundary region with different electrical characteristics (lower threshold voltage). This dimensional addition to the transistor architecture enables precise control over hole extraction timing and location.
Data Source
AI summary
A semiconductor device of embodiments includes: a transistor region including a semiconductor layer having a first face and a second face opposite to the first face, a first transistor having a first gate electrode provided on a first face side of the semiconductor layer, and a second transistor having a second gate electrode provided on a second face side of the semiconductor layer; and an adjacent region adjacent to the transistor region and including the semiconductor layer and a third transistor having a third gate electrode electrically connected to the second gate electrode and provided on the second face side of the semiconductor layer and the third transistor having an absolute value of a threshold voltage smaller than an absolute value of a threshold voltage of the second transistor.