Split Gate Power Transistor with Body Extension Region
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Solution Overview
Problem
Conventional power MOSFETs face limitations in switching speed due to high gate charge requirements, which increases the size and cost of switch-mode power supply (SMPS) components and reduces efficiency.
Innovation Solution
The split gate power transistor configuration, which includes a doped substrate with a gate oxide layer and a split polysilicon layer separated by a gap, reduces gate capacitance by removing the polysilicon over the transition region and using a field plate electrically coupled to the source, thereby reducing gate charge and allowing faster switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional power MOSFETs use a continuous polysilicon gate over the transition region, then the gate provides adequate control and protection, but the gate capacitance increases leading to higher gate charge requirements
Solution Approach 1:
The continuous polysilicon gate is segmented into two separate gates with a gap between them, positioned over the transition region. This segmentation removes the polysilicon material that contributes to gate capacitance while maintaining the necessary gate control function through the coordinated operation of the two separate gates. The gap between gates eliminates the capacitive coupling that would otherwise increase gate charge requirements.
Solution Approach 2:
The polysilicon gate material is extracted or removed from the transition region entirely, replacing it with a gap. This extraction eliminates the source of excessive gate capacitance in the transition region while the remaining gate structures over the channel and drift regions continue to provide the necessary control and protection functions.
2Productivity
If the polysilicon gate is removed over the transition region to reduce gate capacitance, then gate charge decreases, but the transition region loses gate control
Solution Approach 1:
The gate structure is segmented such that one gate covers the channel region and another gate covers the drift region, with the transition region left uncovered (gap). This segmentation allows the transition region to be excluded from capacitive coupling while the adjacent gates maintain control over their respective regions, enabling faster switching without sacrificing transition region integrity.
Solution Approach 2:
The gap between the two gates acts as an intermediary structure that mediates between the need for reduced gate capacitance and the need for transition region control. The gap eliminates capacitive coupling while the coordinated operation of the two separate gates maintains the necessary control functions through the channel and drift regions.
3Ease of manufacture
If a continuous polysilicon gate is used, then manufacturing is simpler, but the gate plate extends over the trench increasing complexity
Solution Approach 1:
The gate plate is segmented into two separate polysilicon gates rather than forming a continuous structure over the trench. This segmentation simplifies the manufacturing process by allowing independent formation and optimization of each gate structure, while reducing the overall device complexity by eliminating the need for a continuous gate plate that would require complex trench integration.
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 gate charge by approximately 50%, enabling higher switching frequencies and smaller component sizes while maintaining efficiency, and is applicable to all switchable power supply integrated circuits.
Implementation Method 1
The substrate is doped to include one or more body extension regions along a length of the device, underneath the gap. Introduction of the body extension region provides an effective sink for the hole inversion charge that attempts to form under the field plate and forces that region to go into deep-depletion
Implementation Method 2
The split gate power transistor configuration, which includes a doped substrate with a gate oxide layer and a split polysilicon layer separated by a gap, reduces gate capacitance by removing the polysilicon over the transition region
Data Source
AI summary
A split gate power transistor includes a doped substrate, a gate oxide layer on the substrate, and a split polysilicon layer over the gate oxide layer, which forms a polysilicon gate positioned over a channel region and a first portion of a transition region and a polysilicon field plate positioned over a second portion of the transition region and a shallow trench isolation region. The two polysilicon portions are separated by a gap. The field plate is electrically coupled to a source of the split gate power transistor. One or more body extension regions, each having the same doping type as the body substrate, extend at least underneath the edge of the field plate adjacent to the gap. The body extension regions force the portion of the transition region underneath the field plate into deep-depletion, thereby preventing the formation of a hole inversion layer in this region.