MOSFET Drift Layer Structure for Higher Current Density
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Solution Overview
Problem
Existing high power MOSFETs face challenges in increasing current density within a smaller die size without compromising performance.
Innovation Solution
The design incorporates a substrate with specific dopant concentrations and layer structures, including a recessed and protruding drift layer with a tee-shaped portion, well, source, and insulating layers, to enhance current flow efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional MOSFET structures are used, then manufacturing is simpler, but current density and power handling capability are limited
Solution Approach 1:
The drift layer is segmented into multiple regions with different dopant concentrations (first drift layer with lower concentration, second drift layer with higher concentration). This segmentation allows optimization of current flow in different regions, enabling higher current density while managing electric field distribution to prevent breakdown.
Solution Approach 2:
Different regions of the transistor are assigned different dopant concentrations tailored to their specific functional requirements. The source/drain regions have higher dopant concentrations for low resistance contacts, while the drift layer has graded concentrations for electric field management. This local optimization enables high current density without compromising breakdown voltage.
2Reliability
If dopant concentrations are increased to enhance current flow, then conductivity improves, but breakdown voltage decreases
Solution Approach 1:
The dopant concentration is varied spatially across different regions of the transistor. The drift layer exhibits a gradient from lower concentration near the gate (maintaining high breakdown voltage) to higher concentration near the drain (enhancing current flow). This parameter optimization resolves the trade-off between conductivity and breakdown voltage.
Solution Approach 2:
Instead of using uniform dopant concentration throughout, the patent introduces a vertical dimension to dopant distribution with multiple drift layer regions at different depths and concentrations. This multi-dimensional doping strategy enables simultaneous optimization of both breakdown voltage (protected by lower concentration regions) and current flow (enhanced by higher concentration regions).
Data Source
AI summary
A transistor having a drain layer formed within a substrate. A drift layer formed over the drain layer, the drift layer having a recessed portion and a protruding portion with a tee-shaped portion. A well layer formed over the recessed portion of the drift layer. A body layer formed over a first portion of the well layer. A source layer formed over a second portion of the well layer. A JFET layer formed within the tee-shaped portion of the drift layer. An insulating layer formed over a portion of the source layer, over a fourth portion of the well layer along the sides of the protruding portion of the drift layer, and over the tee-shaped portion of the drift layer. A gate electrode formed over the insulating layer.