Trench-Gate Charge-Balance Structure for Low Rdson and High BVdss
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Solution Overview
Problem
Existing charge-balance power devices face a trade-off between low on-state source-to-drain resistance (Rdson) and high reverse-biasing voltage (BVdss), as increasing epitaxial layer thickness or resistivity to achieve high BVdss results in higher Rdson, and current column structures complicate manufacturing and increase parasitic capacitance.
Innovation Solution
A charge-balance power device with a trench gate structure and columnar regions of opposite conductivity type, where the columnar regions are spaced apart from the body and drain terminal, and a dual epitaxial layer structure with varying doping concentrations to maintain low Rdson and high BVdss without increasing horizontal device area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the epitaxial layer is increased to withstand high reverse voltage, then the breakdown voltage (BVdss) is improved, but the on-state source-to-drain resistance (Rdson) increases
Solution Approach 1:
The patent applies local quality by creating columnar regions with high doping concentration in specific locations within the epitaxial layer, while maintaining lower doping in other regions. This allows the device to achieve low on-state resistance in the columnar regions without compromising the overall breakdown voltage capability of the epitaxial layer structure.
Solution Approach 2:
The patent transitions from a planar structure to a three-dimensional columnar structure by forming vertically extending columnar regions. This dimensional change allows the device to exploit the entire volume of the epitaxial layer, increasing the effective conducting area and reducing on-state resistance without increasing the horizontal device footprint.
2Strength
If the resistivity of the epitaxial layer is increased to achieve high reverse voltage, then the breakdown voltage (BVdss) is improved, but the on-state source-to-drain resistance (Rdson) increases
Solution Approach 1:
The patent creates regions with different doping concentrations within the epitaxial layer - columnar regions with high doping for low resistance and surrounding regions with lower doping for high breakdown voltage. This local differentiation resolves the contradiction between resistivity and on-state resistance.
3Reliability
If a column structure is used to reduce on-state resistance, then the on-state epitaxial resistance (Repi) is reduced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent segments the epitaxial layer into distinct columnar regions separated by trenches. This segmentation allows independent formation and doping of each columnar region, simplifying the manufacturing process compared to forming a continuous complex structure, while still achieving the benefit of reduced on-state resistance through increased perimeter utilization.
4Reliability
If column structures are used to increase body-drain perimeter, then the on-state resistance is reduced, but parasitic capacitance increases
Solution Approach 1:
The patent extracts the harmful parasitic capacitance effect by introducing trenches that electrically isolate the columnar regions from each other and from the drain terminal. This removal of parasitic capacitance pathways allows the device to maintain low on-state resistance through increased perimeter while eliminating the associated parasitic effects.
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 effectively reduces on-state source-drain resistance while maintaining high breakdown voltage, overcoming manufacturing complexities and parasitic capacitance issues of previous designs.
Implementation Method 1
it is possible to obtain charge-balance or charge compensation between the dopant of the columns, of a P type, and the charge of the epitaxial layer, of an N type, so that the total charge of the columns will be equal and of opposite sign with respect to the total charge of the epitaxial layer
Implementation Method 2
behaving as an insulating layer, enables high values of reverse voltage (breakdown voltage), with an electrical extension field with a profile that is practically uniform
Data Source
AI summary
A charge-balance power device includes a semiconductor body having a first conductivity type. A trench gate extends in the semiconductor body from a first surface toward a second surface. A body region has a second conductivity type that is opposite the first conductivity type, and the body region faces the first surface of the semiconductor body and extends on a first side and a second side of the trench gate. Source regions having the first conductivity type extend in the body region and face the first surface of the semiconductor body. A drain terminal extends on the second surface of the semiconductor body. The device further comprises a first and a second columnar region having the second conductivity, which extend in the semiconductor body adjacent to the first and second sides of the trench gate, and the first and second columnar regions are spaced apart from the body region and from the drain terminal.