Circular Trench MOSFET for High Breakdown Voltage
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Solution Overview
Problem
Conventional trench MOSFETs face limitations in breakdown voltage due to high electrical field density and curvature-induced stress, as well as restricted improvements in threshold voltage and Specific On Resistance (RDSON) with current semiconductor technologies.
Innovation Solution
The development of a transistor with circular trench openings and an epitaxial layer, featuring a gate oxide and gate conductor within the trench, which reduces stress and enhances breakdown voltage by providing a uniform electrical field and lower threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional trench MOSFET structures are used, then fabrication is simplified, but breakdown voltage is limited due to high electrical field density and curvature-induced stress
Solution Approach 1:
The patent applies spheroidality by forming circular trenches instead of conventional straight or angled trenches. The circular geometry distributes electrical field lines uniformly around the gate conductor, eliminating field concentration at corners or edges. This curvature-based design reduces peak electrical field density while maintaining fabrication simplicity through standardized circular patterning processes.
2Ease of manufacture
If conventional trench MOSFET structures are used, then manufacturing is easier, but threshold voltage improvement is restricted
Solution Approach 1:
The patent applies local quality by creating non-uniform doping profiles within the circular trench structure. Different regions of the circular trench can have different dopant concentrations, allowing precise control of threshold voltage characteristics. The circular geometry provides symmetric local regions that can be independently doped to achieve desired electrical characteristics while maintaining overall manufacturing simplicity.
3Ease of manufacture
If conventional trench MOSFET structures are used, then fabrication is simpler, but Specific On Resistance (RDSON) improvement is limited
Solution Approach 1:
The circular trench geometry provides uniform electrical field distribution that reduces peak field density, enabling lower on-resistance operation. The curved walls of circular trenches optimize the depletion region formation, reducing resistance in the on-state while maintaining fabrication simplicity through circular patterning techniques that are compatible with existing manufacturing processes.
4Reliability
If circular trench openings are used, then breakdown voltage increases and electrical field uniformity improves, but fabrication complexity increases
Solution Approach 1:
The patent employs circular trench geometry to achieve uniform electrical field distribution, which directly increases breakdown voltage by eliminating field concentration points. While circular patterning may seem more complex than straight trenches, the invention maintains fabrication simplicity by using standard circular lithography and etching processes that are well-established in semiconductor manufacturing, thus not significantly increasing overall fabrication 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 circular trench MOSFET design achieves higher breakdown voltage up to 1000V and lower RDSON, along with improved heat dissipation and packing density, while simplifying fabrication and reducing plasma loading effects.
Implementation Method 1
growing an epitaxial layer on a substrate
Implementation Method 2
depositing an oxide on the epitaxial layer
Implementation Method 3
coating a photo resist over the oxide
Implementation Method 4
etching the oxide and epitaxial layer to form at least one circular trench
Implementation Method 5
growing a second oxide layer on the trench surfaces
Implementation Method 6
forming a gate conductor within the at least one trench
Data Source
AI summary
A transistor and a method of fabricating a transistor, including a metal oxide deposited on an epitaxial layer, a photo resist deposited and patterned over the metal oxide and the metal oxide and epitaxial layer are etched to form at least one circular trench, wherein the trench surfaces are defined by the epitaxial layer. An oxide layer is grown on the trench surfaces of each trench, and a gate conductor is formed within the at least one trench.