Charge-Balance Trench Power 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 trench-gate structures lead to parasitic capacitance and manufacturing complexities.
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 optimize charge balance and reduce Rdson without compromising BVdss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the epitaxial layer is increased to achieve high reverse voltage (BVdss), then the breakdown voltage 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 different doping concentrations (first concentration in the drift region, second concentration in the columnar regions) within the epitaxial layer. This allows different portions of the epitaxial layer to have optimized properties: the columnar regions provide charge balance for high breakdown voltage, while the drift region maintains low resistance for low Rdson, resolving the contradiction between these two parameters.
2Strength
If the resistivity of the epitaxial layer is increased to achieve high reverse voltage (BVdss), then the breakdown voltage is improved, but the on-state source-to-drain resistance (Rdson) increases
Solution Approach 1:
The patent implements local quality by establishing different doping concentrations in different regions: the drift region has a first doping concentration optimized for low resistance, while the columnar regions have a second doping concentration optimized for charge balance and breakdown voltage. This spatial differentiation of doping properties allows simultaneous optimization of both Rdson and BVdss, resolving the contradiction between resistivity and on-state resistance.
3Reliability
If a trench-gate structure with columnar regions is used to reduce Rdson, then the on-state resistance is improved, but parasitic capacitance and manufacturing complexity increase
Solution Approach 1:
The patent applies segmentation by dividing the epitaxial layer into distinct columnar regions and drift regions with different doping concentrations. This segmentation allows independent optimization of each region's properties and simplifies the manufacturing process by enabling separate doping steps for each region, reducing the complexity of achieving the desired charge balance while maintaining low Rdson.
Solution Approach 2:
The patent utilizes parameter changes by varying the doping concentration parameter across different regions of the epitaxial layer. The first doping concentration in the drift region and the second doping concentration in the columnar regions are independently controlled, allowing optimization of both electrical performance and manufacturing processes, thereby reducing parasitic capacitance and manufacturing complexity while maintaining low on-state resistance.
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 the limitations of previous designs by ensuring complete depletion and uniform electrical field profiles, thus enhancing the device's performance and manufacturing reliability.
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
These conditions entail complete depletion of the free carriers both in the epitaxial layer and in the columns so as to provide an area without carriers, which, behaving as an insulating layer, enables high values of reverse voltage
Implementation Method 3
A dual epitaxial layer structure with varying doping concentrations to optimize charge balance and reduce Rdson without compromising BVdss
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.