Graded Drift Region Vertical Transistor Breakdown Voltage
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Solution Overview
Problem
Vertical transistors face a trade-off between breakdown voltage and ON resistance, where increasing impurity concentration in the drift layer improves ON resistance but decreases breakdown voltage, and vice versa, limiting the performance of semiconductor devices.
Innovation Solution
A semiconductor device design with a drift region having distinct impurity concentration zones, including a high impurity concentration intermediate region between lower and upper portions, and field plate electrodes to optimize electric field distribution and enhance breakdown voltage while reducing ON resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impurity concentration of drift layer is increased, then ON resistance decreases, but breakdown voltage decreases
Solution Approach 1:
The drift layer is divided into three regions with different impurity concentrations: a first region with lower impurity concentration near the drain, a second region with intermediate impurity concentration in the middle, and a third region with higher impurity concentration near the body region. This local quality variation allows each region to contribute differently - the low impurity region maintains high breakdown voltage while the high impurity region reduces ON resistance, resolving the trade-off between these two parameters.
Solution Approach 2:
The drift layer is segmented into multiple regions with graded impurity concentrations rather than using a uniform concentration. This segmentation into first, second, and third regions with progressively higher impurity concentrations enables the structure to simultaneously achieve high breakdown voltage (through the low impurity first region) and low ON resistance (through the high impurity third region).
2Reliability
If impurity concentration of drift layer is decreased, then breakdown voltage increases, but ON resistance increases
Solution Approach 1:
Different regions of the drift layer have different impurity concentrations optimized for different functions. The first region with lower impurity concentration is positioned where high electric field withstand is needed (near drain), while the third region with higher impurity concentration is positioned where low resistance is needed (near body region). This local optimization resolves the contradiction between breakdown voltage and ON resistance.
Solution Approach 2:
The impurity concentration parameter is changed progressively across the drift layer thickness, creating a graded structure. By changing the impurity concentration from low in the first region to high in the third region, the patent achieves both high breakdown voltage (due to low impurity regions) and low ON resistance (due to high impurity regions), eliminating the need to choose one parameter at the expense of the other.
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 design effectively increases drain-source breakdown voltage and decreases ON resistance, improving the trade-off relationship between these two critical parameters in vertical transistors.
Implementation Method 1
An electric field distribution of a drift layer is changed by the presence of a field plate electrode, whereby a breakdown voltage of a vertical transistor can be increased
Data Source
AI summary
A semiconductor device includes a semiconductor layer that has a first surface and a second surface, a drift region of a first conductivity type in the semiconductor layer, a body region of a second conductivity type between the drift region and the first surface, a source region of first conductivity type, a first gate electrode, a second gate electrode with the body region interposed between the first gate electrode and the second gate electrode, first and second gate insulating films, a first field plate electrode between the second surface and the first gate electrode, a second field plate electrode between the second surface and the second gate electrode, a first region of the first conductivity type in the drift region, a second region between the first region and the body region, and a third region between the second region and the body region.