IGBT Floating-Gate Structure for Fast Reverse Recovery
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Solution Overview
Problem
IGBT devices experience long reverse recovery times due to minority carrier injection, leading to high reverse recovery currents.
Innovation Solution
The IGBT device incorporates an n-type collector region, p-type collector region, and multiple MOSFET cells with specific gate structures and emitter regions to reduce reverse recovery time, including a first MOSFET cell with a low threshold voltage for increased reverse current and a second MOSFET cell with a shorter current channel to control chip size and enhance recovery speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the IGBT device uses a conventional structure with body diode, then the device can conduct reverse current, but the reverse recovery time becomes long due to minority carrier injection
Solution Approach 1:
The patent segments the MOSFET cell into two independent parts: a first MOSFET cell with a floating gate that forms a p-n junction diode for reverse current conduction, and a second MOSFET cell for forward current control. This segmentation allows the reverse recovery path to be separated from the forward conduction path, enabling independent optimization of reverse recovery speed without affecting forward operation.
Solution Approach 2:
The floating gate structure acts as an intermediary element that enables the first MOSFET cell to function as a fast reverse recovery diode. The floating gate creates a p-n junction that provides a dedicated reverse current path, mediating between the body diode and the control circuitry to achieve fast reverse recovery while maintaining simple control logic.
2Area of stationary object
If the IGBT device reduces chip size, then the device becomes more compact, but the reverse recovery speed may be compromised
Solution Approach 1:
The patent utilizes the vertical dimension by forming the floating gate and p-n junction structure in the depth direction of the chip, rather than expanding the lateral footprint. The first MOSFET cell with floating gate is positioned to utilize the vertical space between existing structures, allowing fast reverse recovery functionality to be added without increasing the chip's planar area.
Solution Approach 2:
The first MOSFET cell with floating gate serves multiple functions: it acts as a fast reverse recovery diode during reverse current flow, while also contributing to forward current conduction when activated. This multi-functionality allows the device to achieve fast reverse recovery without adding dedicated separate structures that would increase chip size.
3Reliability
If the IGBT device increases reverse current through first MOSFET cell, then the reverse recovery speed improves, but the device complexity increases
Solution Approach 1:
The patent merges the reverse recovery function with the existing MOSFET cell structure by integrating the floating gate into the conventional MOSFET architecture. The first MOSFET cell combines the floating gate diode functionality with the standard source-drain channel, eliminating the need for separate reverse recovery structures and reducing overall device complexity while achieving fast reverse recovery.
Solution Approach 2:
The floating gate structure is self-configuring during fabrication and operation. The p-n junction diode formed by the floating gate automatically provides the reverse current path without requiring external control signals or additional control circuitry. The structure serves itself to enable fast reverse recovery, reducing the complexity of control systems.
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 reduces reverse recovery time and current through the body diode, allowing for a smaller chip size while maintaining fast reverse recovery speed.
Implementation Method 1
the n-type floating gate is in contact with the p-type body region to form a p-n junction diode through the one opening
Implementation Method 2
the first MOSFET cell has a low threshold voltage, so that the first MOSFET cell is turned on at a low gate voltage (or a voltage of 0 V), thus the reverse current flowing through the first MOSFET cell can be increased
Implementation Method 3
a current channel is formed inside the MOS transistor and a base current is supplied to the bipolar transistor so that the IGBT device is turned on. When the gate-emitter voltage is smaller than the threshold voltage Vth of the MOS transistor, the current channel inside the MOS transistor will be turned off
Data Source
AI summary
Provided is an insulated gate bipolar transistor (IGBT) device. The IGBT device includes p-type body regions located on a top of an n-type drift region, a first n-type emitter region located within the p-type body region; a first gate structure located over the p-type body region, where the first gate structure includes a first gate dielectric layer, a first gate and an n-type floating gate which are located above the first gate dielectric layer, where the n-type floating gate is located on a side close to the n-type drift region in a lateral direction; an insulating dielectric layer located between the n-type floating gate and the first gate; and one opening in the first gate dielectric layer. The n-type floating gate is in contact with the p-type body region to form a p-n junction diode through the one opening.