Trench MOSFET Rectifier With Variable Oxide Thickness
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Solution Overview
Problem
Conventional power semiconductor rectifiers, such as PN diodes and Schottky diodes, face limitations including high cost, complex fabrication, and inefficiencies in meeting modern requirements for low voltage, high current, and high efficiency due to their inherent forward voltage drops and reverse recovery characteristics.
Innovation Solution
The development of a trench MOSFET rectifier device with oxide layers of varying thicknesses and a p-doped region to enhance reverse breakdown voltage, along with conductive material-filled contact trenches for connecting source, body, and gate regions, addresses these limitations by providing a lower turn-on voltage and improved reverse blocking capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a PN diode is used for rectification, then the device structure is simple, but the forward voltage drop is high (0.6-0.8V) leading to low efficiency
Solution Approach 1:
The patent changes the fundamental operating parameters by transitioning from a PN junction diode to a MOSFET-based rectifier. The MOSFET structure with gate control allows for variable resistance operation, enabling the rectifier to achieve lower forward voltage drop (0.3-0.5V) compared to conventional PN diodes (0.6-0.8V) while maintaining manufacturing feasibility through standard semiconductor fabrication processes.
2Loss of energy
If a Schottky diode is used to reduce forward voltage drop, then the forward voltage drop decreases (0.2-0.4V), but the fabrication process becomes more complex and cost increases
Solution Approach 1:
The patent employs a MOSFET structure that replicates the low forward voltage drop characteristic of Schottky diodes (achieving 0.3-0.5V) while using standard silicon-based fabrication processes instead of the complex Schottky metallization processes. This copying of the electrical characteristic through a different physical structure avoids the fabrication complexity and cost penalties of Schottky diodes.
3Productivity
If conventional rectifiers are used, then the device can be manufactured, but the reverse recovery characteristics are poor leading to excessive power loss with large output current
Solution Approach 1:
The MOSFET-based rectifier introduces dynamic control through the gate terminal, allowing the device to actively modulate its channel resistance during switching transitions. This dynamic operation enables much faster reverse recovery compared to the passive, fixed characteristics of conventional diodes, significantly reducing reverse recovery losses especially at large output currents while maintaining high productivity.
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 trench MOSFET rectifier device achieves a lower turn-on voltage of 0.3-0.5V, improved reverse breakdown voltage, and reduced power loss, making it suitable for high-voltage and high-power applications while simplifying the fabrication process and reducing costs.
Implementation Method 1
oxide layers having different thicknesses formed in different regions of the devices
Implementation Method 2
a p-dope region at the bottom of the trench is used to enhance the reverse breakdown voltage
Implementation Method 3
A conductive material fills a second plurality of trenches, which are the contact trenches, and forms ohmic contacts with the source region, body region, and gate region
Data Source
AI summary
A trench MOSFET rectifier includes oxide layers having different thicknesses formed in different regions of the devices. The rectifying device also includes a source region of first conductivity type at a surface of each mesa region and a body region of a second conductivity type beneath each source region. The rectifying device also includes a dielectric layer lining the bottom and sidewall surfaces of the trenches, the portion of the dielectric layer on the bottom surface being thicker than the portion on the sidewall surface. A doped region underlies each of the first plurality of trenches. A polycrystalline silicon region filling each of the first plurality of trenches to form a gate region in each trench. A conductive material fills a plurality of contact trenches and forms ohmic contacts with the source region, body region, and gate region.