Split Gate MOSFET with Field Plate Extension
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Solution Overview
Problem
Conventional MOSFETs in switch-mode power supplies require high gate charge for switching, leading to increased size, cost, and power losses due to the need for larger discrete components in the gate drive circuit, limiting switching frequency and efficiency.
Innovation Solution
A split gate power transistor configuration with a doped substrate, a gate oxide layer, and a split polysilicon layer, where the polysilicon layer is cut into electrically isolated portions forming a polysilicon gate and a field plate separated by a gap, reducing gate capacitance and charge by approximately 50% through deep-depletion of the transition region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional MOSFET configuration is used, then device structure is simple, but gate charge is high leading to increased component size and reduced switching frequency
Solution Approach 1:
The gate structure is segmented into two electrically isolated polysilicon portions: a first portion forming the polysilicon gate positioned over the channel region, and a second portion forming the polysilicon field plate positioned over the transition region and shallow trench isolation region. This segmentation reduces gate capacitance and gate charge while maintaining device functionality.
Solution Approach 2:
The gate structure is extracted from a single continuous polysilicon layer and separated into distinct gate and field plate portions by a gap. This extraction eliminates the capacitive coupling between the gate and drain that would otherwise increase gate charge, while the field plate maintains voltage support functionality.
2Volume of moving object
If discrete MOSFETs are used in SMPS, then individual device performance is maintained, but overall system size and cost increase
Solution Approach 1:
The MOSFET is integrated with associated circuitry into a single monolithic device structure, combining the power switching function with the gate drive functionality. This integration reduces the overall system size and component count while maintaining reliable operation through optimized internal device architecture.
3Productivity
If higher switching frequency is achieved, then component size is reduced, but gate charge requirements increase leading to higher power losses
Solution Approach 1:
By segmenting the gate into electrically isolated portions, the total gate capacitance is reduced, which directly reduces the gate charge required for switching. This enables higher switching frequencies with lower gate drive power losses.
Solution Approach 2:
The gate structure parameters are changed by introducing a gap and separating the polysilicon into distinct portions, which fundamentally alters the capacitive characteristics and reduces the gate charge parameter, enabling efficient high-frequency operation.
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
The split gate configuration enables faster switching and higher frequency operation with reduced component size and cost, improving efficiency and reliability by minimizing gate charge and feedback capacitance, while maintaining breakdown voltage and hot carrier lifetime.
Implementation Method 1
reducing gate capacitance and charge by approximately 50% through deep-depletion of 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 and a polysilicon field plate. 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 polysilicon extension tabs extend from the field plate to at least above the edge of the first doped region. The polysilicon gate is cut to form a cut-out region for the end of each polysilicon extension tab extending toward the body substrate. The one or more polysilicon extension tabs 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.