Trench Power MOSFET Gate PN Junction Series Capacitance
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Solution Overview
Problem
High intrinsic gate-to-drain capacitance in trench power MOSFETs limits switching speed and makes them unsuitable for high-frequency circuits, as it increases switching loss.
Innovation Solution
A trench power MOSFET with a gate having a PN junction is developed, where the PN junction is formed by creating upper and lower doped regions with different doping types, reducing the effective capacitance between the gate and drain by generating junction capacitance in series with the intrinsic gate-to-drain capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a trench gate structure is used to improve packing density, then packing density increases, but intrinsic gate-to-drain capacitance increases leading to higher switching loss
Solution Approach 1:
The gate is segmented into multiple doped regions (first doped region, second doped region, third doped region) with different doping types and concentrations. This segmentation creates multiple PN junctions within the gate structure, which divides the capacitance into series components, thereby reducing the effective gate-to-drain capacitance while maintaining the trench gate's high packing density advantage
Solution Approach 2:
The doping parameters (type and concentration) are changed at different vertical positions within the gate. The first doped region has a first doping type and first concentration, the second doped region has a second doping type and second concentration, and the third doped region has a third doping type and third concentration. These parameter changes create PN junctions that reduce effective capacitance
2Speed
If intrinsic gate-to-drain capacitance is reduced to decrease switching loss, then switching speed improves, but device complexity increases due to multiple doped regions
Solution Approach 1:
Multiple doped regions are merged within a single gate structure, forming an integrated gate that contains the first doped region, second doped region, and third doped region. This merging approach reduces effective capacitance to improve switching speed while consolidating the complexity within one unified gate component rather than separate structures
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 reduction in effective capacitance between the gate and drain minimizes switching loss and enhances the switching speed of the trench power MOSFET, making it more suitable for high-frequency applications.
Implementation Method 1
The gate formed in the trench includes an upper doped region and a lower doped region which have different types of doping to form a PN junction
Implementation Method 2
Since a junction capacitance (Cj) of the PN junction is generated under reverse bias, and the junction of capacitance is in series with the intrinsic gate-to-drain capacitance (Cgd), the effective capacitance between the gate and the drain can be reduced
Implementation Method 3
performing a base doping process to form a first doped region; forming a plurality of trench gate structures in the epitaxial layer and the first doped region, in which each of trench gate structure includes an upper doped region and a lower doped region to form a PN junction
Implementation Method 4
performing a thermal diffusion process to form a source region and a body region, in which the first-type doped region and the second-type doped region diffuse and respectively form a lower doped region and an upper doped region during the thermal diffusion process
Data Source
AI summary
A trench power MOSFET and a manufacturing method thereof are provided. The gate of the trench power MOSFET includes an upper doped region and a lower doped region which have different types of doping to form a PN junction. As such, when the trench power MOSFET is in operation, a junction capacitance formed at the PN junction is in series with the intrinsic gate-to-drain capacitance. Accordingly, the effective capacitance between the gate and the drain may be reduced.