Power MOSFET Parallel Current Paths for Low On-Resistance
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Solution Overview
Problem
Power MOSFETs face challenges in minimizing conduction power losses due to high specific on-resistance, which is dominated by channel and drift region resistances, and require complex fabrication to ensure proper functionality and gate oxide reliability.
Innovation Solution
The solution involves combining dynamically inverted channel regions with statically inverted drift regions in separate locations of semiconductor material, using immobile electrostatic charge to create parallel current paths through both p-type and n-type drift regions, thereby reducing on-resistance and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If fixed or permanent charges are incorporated in trenches to form induced electron drift region, then on-resistance is reduced, but fabrication complexity increases and gate oxide reliability is compromised
Solution Approach 1:
The device is divided into separate functional regions: a conventional MOSFET structure for channel formation and a static inversion region with fixed charges for drift region formation. This segmentation allows each region to be optimized independently, simplifying fabrication while maintaining the low on-resistance benefit
Solution Approach 2:
The gate electrode is extracted from the trench containing the fixed charges. By separating the gate structure from the fixed charge region, the patent eliminates the need for precise positioning of the gate relative to the induced drift region, thereby simplifying fabrication processes while still achieving the desired electrical characteristics
2Loss of energy
If fixed or permanent charges are incorporated in trenches to form induced electron drift region, then on-resistance is reduced, but gate oxide reliability deteriorates
Solution Approach 1:
The gate electrode is completely removed from the trench containing the fixed charges. This extraction eliminates the direct interaction between the gate oxide and the high electric field regions near the fixed charges, thereby protecting gate oxide reliability while preserving the low on-resistance characteristic through the static inversion layer
Solution Approach 2:
A dielectric material containing fixed charges serves as an intermediary between the P-layer and the induced electron drift region. This dielectric layer with embedded fixed charges creates the necessary electric field for inversion without requiring the gate oxide to be in direct proximity to high field regions, thus maintaining gate oxide reliability
3Loss of energy
If gate electrode is placed in close proximity to induced electron drift region to provide current continuity, then current conduction is improved, but fabrication precision requirements increase
Solution Approach 1:
The gate electrode is extracted from the trench, eliminating the need for precise positioning relative to the induced drift region. Current continuity is maintained through the static inversion layer formed by the fixed charges in the dielectric, which provides a robust conduction path insensitive to fabrication tolerances
Solution Approach 2:
The fixed charges in the dielectric automatically form the static inversion layer and provide current continuity without requiring precise gate positioning. The structure self-adjusts to provide optimal conduction paths through the induced electron drift region, eliminating the need for high-precision gate placement
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 approach reduces on-resistance, simplifies fabrication, enhances breakdown voltage, and improves device reliability by providing multiple current paths and better current spreading.
Implementation Method 1
Positive permanent electrostatic charge can be formed within a device structure by, for example, implanting ions such as Cesium into a dielectric (such as SiO2). The positive permanent charge also forms an induced electron drift region by forming an inversion layer along the interface between the oxide and the P layer.
Data Source
AI summary
Power semiconductor devices, and related methods, where majority carrier flow is divided into paralleled flows through two drift regions of opposite conductivity types.