Trench-Gate MOSFET Shield Electrode for Breakdown Voltage
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Solution Overview
Problem
Conventional trench-gate MOSFETs face limitations in breakdown voltage, transistor ruggedness, and on-resistance due to the high electric field at the bottom of the trench and the thick drift region, which also complicates the integration of Schottky diodes with power MOSFETs.
Innovation Solution
The solution involves forming a dual gate trench MOSFET with a conductive shield electrode and a shield dielectric layer that flares out under the body region, reducing the drift region thickness and improving the channel resistance by incorporating channel enhancement regions and a source plug, while also allowing for monolithic integration with Schottky diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the drift region is made thicker to improve breakdown voltage, then breakdown voltage increases, but on-resistance increases significantly
Solution Approach 1:
The patent applies local quality by creating different doping concentrations in specific regions: the body region has a first doping concentration while the drift region has a second doping concentration. This allows the drift region to be optimized for breakdown voltage while the body region compensates for on-resistance, resolving the contradiction between these two parameters.
Solution Approach 2:
The patent changes the doping concentration parameter from uniform to non-uniform, with the body region having a higher doping concentration than the drift region. This parameter change enables the drift region to maintain thickness for high breakdown voltage while the body region provides low resistance paths, simultaneously improving both breakdown voltage and on-resistance.
2Reliability
If the trench depth is increased to improve gate control, then gate control improves, but the high electric field at the bottom curvature worsens breakdown voltage and transistor ruggedness
Solution Approach 1:
The patent applies local quality by differentiating the doping concentrations between the body region and drift region. The higher doping in the body region specifically addresses the high electric field area at the trench bottom, while the lower doping in the drift region maintains breakdown voltage, thus resolving the contradiction between gate control and breakdown voltage.
Solution Approach 2:
The body region acts as an intermediary between the gate and the drift region. It provides the necessary gate control while its higher doping concentration mitigates the harmful electric field effects at the trench bottom, protecting the drift region and improving overall device ruggedness.
3Reliability
If a dual gate structure with shield electrode is used to reduce gate-drain capacitance, then gate-drain capacitance decreases, but device complexity increases
Solution Approach 1:
The patent merges the shield electrode function with the existing trench gate structure by forming the shield electrode within the same trench. This integration approach reduces gate-drain capacitance while avoiding the need for separate shielding structures, thus improving performance without proportionally increasing device complexity.
Solution Approach 2:
The shield electrode in the trench serves multiple functions: it acts as a shield to reduce gate-drain capacitance, provides additional gate control, and helps with electric field management. This multi-functionality reduces the need for separate components, thereby improving performance while limiting complexity increase.
Data Source
AI summary
A field effect transistor (FET) includes a body region of a first conductivity type disposed within a semiconductor region of a second conductivity type and a gate trench extending through the body region and terminating within the semiconductor region. The FET also includes a flared shield dielectric layer disposed in a lower portion of the gate trench, the flared shield dielectric layer including a flared portion that extends under the body region. The FET further includes a conductive shield electrode disposed in the trench and disposed, at least partially, within the flared shield dielectric.