Vertical MOSFET Drift Region Grading for Low On-Resistance
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Solution Overview
Problem
There is a need for power MOSFET devices that optimize low on-resistance, switching properties, and device ruggedness while maintaining good switching characteristics and reducing switching losses.
Innovation Solution
A vertical power semiconductor transistor device with a drift region featuring a generally linearly graded first doping profile and a graded second doping profile that increases at a greater rate, optimizing the doping profile to reduce on-resistance and enhance avalanche ruggedness, and employing a field electrode in a trench structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a higher doping concentration is used in the drift region to reduce on-resistance, then on-resistance decreases, but avalanche ruggedness deteriorates
Solution Approach 1:
The drift region is divided into two zones with different doping concentrations: a first drift region with lower doping concentration adjacent to the body region to ensure avalanche ruggedness, and a second drift region with higher doping concentration adjacent to the drain region to reduce on-resistance. This spatial differentiation of doping quality allows simultaneous optimization of both contradictory requirements.
Solution Approach 2:
The drift region is segmented into multiple regions with graded doping profiles. The doping concentration increases gradually from the body region toward the drain region, creating intermediate zones that balance the competing demands of low on-resistance and high avalanche ruggedness, rather than using a single uniform doping level.
2Object-generated harmful factors
If insulation thickness at the trench bottom is increased to reduce drain-induced barrier leakage, then DIBL decreases, but manufacturing complexity increases
Solution Approach 1:
The gate insulation layer is designed with non-uniform thickness: a first thickness in the gate trench and a second, greater thickness at the trench bottom. This localized increase in insulation thickness specifically at the trench bottom provides enhanced protection against DIBL without requiring the entire gate structure to be more complex.
Solution Approach 2:
A field electrode is introduced as an intermediary element between the gate electrode and the drift region. This field electrode, positioned in the extended gate trench, acts as a mediator to control the electric field distribution and reduce DIBL effects without directly increasing the gate insulation thickness throughout the structure.
Data Source
AI summary
A vertical power semiconductor transistor device includes: a drain region of a first conductivity type; a body region of a second conductivity type; a drift region of the first conductivity type which separates the body region from the drain region; a source region of the first conductivity type separated from the drift region by the body region; a gate trench extending through the source and body regions and into the drift region, the gate trench including a gate electrode; and a field electrode in the gate trench or in a separate trench. The drift region has a generally linearly graded first doping profile which increases from the body region toward a bottom of the trench that includes the field electrode, and a graded second doping profile that increases at a greater rate than the first doping profile from an end of the first doping profile toward the drain region.