High Voltage MOSFET Series Resistance Reduction via Segmented Drift
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Solution Overview
Problem
High voltage MOS transistors face increased series resistances due to drift regions with lower doping densities, which can lead to undesirable voltage drops across gate dielectric layers, limiting their operational efficiency.
Innovation Solution
The design incorporates a heavily doped lower drain layer, a drain drift region, a body region, lateral channel regions, and RESURF trenches that extend from the top surface to the lower drain layer, with RESURF conductive elements and dielectric liners to reduce electric fields and adjust resistivity, thereby minimizing series resistances and enhancing operational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drift regions with lower doping densities are used to reduce voltage across gate dielectric layers, then gate dielectric layer integrity is improved, but series resistance increases
Solution Approach 1:
The drift region is segmented into multiple regions with different doping densities. A first drift region has a first doping density while a second drift region has a second doping density that is higher than the first. This segmentation allows the majority of the voltage drop to occur across the lower-doped first drift region, protecting the gate dielectric, while the higher-doped second drift region provides a lower resistance path for current flow.
Solution Approach 2:
Different regions of the drift structure are assigned different doping densities based on their specific functional requirements. The first drift region positioned adjacent to the gate dielectric has lower doping density to reduce electric field stress on the gate dielectric, while the second drift region positioned away from the gate dielectric has higher doping density to reduce series resistance. This local differentiation of material properties optimizes both gate dielectric protection and current conduction.
2Object-affected harmful factors
If higher doping density is used in drift regions, then series resistance is reduced, but voltage across gate dielectric layers increases beyond maximum operating voltages
Solution Approach 1:
The drift region is divided into segments with progressively different doping densities. The first drift region adjacent to the gate dielectric maintains lower doping density to ensure voltage protection, while subsequent drift regions have progressively higher doping densities to progressively reduce series resistance. This segmented approach allows the system to achieve low overall series resistance without compromising gate dielectric integrity.
Solution Approach 2:
The doping density is locally optimized at different positions within the drift region. Regions closer to the gate dielectric have lower doping density to protect against high electric fields, while regions farther away have higher doping density to minimize resistive losses. This spatial variation of material quality enables simultaneous optimization of both protection and conduction functions.
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
This configuration reduces series resistances and recovery currents in high voltage MOS transistors, allowing them to operate effectively at higher drain voltages while maintaining gate dielectric layer integrity.
Implementation Method 1
The drift regions provide voltage drops from the drain contact to the drain portion adjacent to the transistor channel regions, thereby reducing the voltages across the gate dielectric layers
Implementation Method 2
RESURF trenches extending from the top surface to the lower drain layer, with RESURF conductive elements and dielectric liners to reduce electric fields and adjust resistivity
Data Source
AI summary
A semiconductor device containing a high voltage MOS transistor with a drain drift region over a lower drain layer and channel regions laterally disposed at the top surface of the substrate. RESURF trenches cut through the drain drift region and body region parallel to channel current flow. The RESURF trenches have dielectric liners and electrically conductive RESURF elements on the liners. Source contact metal is disposed over the body region and source regions. A semiconductor device containing a high voltage MOS transistor with a drain drift region over a lower drain layer, and channel regions laterally disposed at the top surface of the substrate. RESURF trenches cut through the drain drift region and body region perpendicular to channel current flow. Source contact metal is disposed in a source contact trench and extended over the drain drift region to provide a field plate.