Trench Net IGBT Structure for Conductivity Modulation
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Solution Overview
Problem
Conventional wide trench IGBTs are structurally unstable, mechanically weak, and difficult to manufacture while failing to effectively limit hole escape and promote conductivity modulation.
Innovation Solution
A trench net structure is formed in a P region, separating it into P wells and floating P layers, with an N+ source region in each corner of the P wells and a gate with an oxide layer, allowing for the formation of inversion and accumulation channels that increase electron and hole density, thus enhancing conductivity modulation and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate width is increased to create a wide trench IGBT structure, then conductivity modulation is enhanced, but structural stability and mechanical strength deteriorate
Solution Approach 1:
The gate structure is divided into multiple gates arranged in parallel, each with its own trench. This segmentation allows the device to achieve wide effective gate width for conductivity modulation while maintaining individual gate structural integrity and mechanical strength.
2Reliability
If the gate width is increased to create a wide trench IGBT structure, then conductivity modulation is enhanced, but manufacturing difficulty increases
Solution Approach 1:
The device uses multiple separate trenches for gates rather than one wide trench, making the structure easier to manufacture using standard semiconductor fabrication processes while still achieving the desired conductivity modulation effect.
3Ease of manufacture
If conventional trench structure is used, then manufacturing is easier, but hole escape is not effectively limited
Solution Approach 1:
An N-type buffer layer is introduced as an intermediary between the P-type collector layer and the N-type drift layer. This buffer layer acts as a barrier to limit hole escape from the drift layer into the collector layer, reducing harmful effects while maintaining manufacturing feasibility.
4Device complexity
If conventional trench structure is used, then device complexity is lower, but conductivity modulation is insufficient
Solution Approach 1:
Multiple gates are used instead of a single gate, segmenting the device structure to enhance conductivity modulation through increased electric field distribution while maintaining reasonable device complexity.
Solution Approach 2:
The N-type buffer layer serves as an intermediary that enhances conductivity modulation by controlling carrier distribution and reducing harmful hole escape, thereby improving device performance without excessive complexity.
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
The solution provides a low-loss IGBT with improved conductivity modulation and structural stability by isolating floating P layers from the emitter electrode and preventing hole escape, resulting in a more efficient power semiconductor device.
Implementation Method 1
The gate is surrounded by an oxide layer such that the oxide layer is provided between the gate and the N- layer, the P wells and the N+ source regions
Implementation Method 2
The conductivity of a semiconductor may be varied in proportion to the density of charge carriers. For example, increasing the amount of charge carriers increases the conductivity of the device. This phenomenon is referred to as 'conductivity modulation.'
Implementation Method 3
In operation, when a positive voltage is applied to the gate, electrons move from the N+ source regions and the P wells into the N-layer and the N layer
Implementation Method 4
In the opposite direction, holes from the P+ layer move into the N layer and the N- layer. The holes in the N- layer easily traverse the junction and into the P wells
Data Source
Figure 1a~1c
Figure 2a~2c
Figure 3a~3b
AI summary
A trench structure of an insulated gate bipolar transistor (IGBT) is formed as a trench net in a P region and extends into an N- layer. The trench net separates the P region into P wells and floating P layers. The P wells contact an emitter electrode while the floating P layers are not in direct contact with the emitter electrode. A gate formed of conductive material and having a surrounding insulation oxide layer is formed in the trench net. An N+ layer may be formed above each floating P layer under the gate. The floating P layers are isolated from the gate and are also not connected to the emitter electrode.