Embedded Field Electrodes in Power MOSFETs
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Solution Overview
Problem
Trench power MOSFETs face a trade-off between reducing on-state resistance (RDSon) and maintaining high reverse voltage blocking capability, with existing techniques either increasing on-state resistance or being costly and difficult to implement.
Innovation Solution
The implementation of embedded field electrodes in the power semiconductor device, where the field electrodes are formed in trenches independent of the gate electrodes, allowing for thinner dielectric insulation and reduced on-state resistance without compromising reverse voltage blocking capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If field plates are placed in the drift region and electrically connected to gate or source potential, then reverse voltage blocking capability is improved, but on-state resistance increases due to thick field plate dielectric
Solution Approach 1:
The invention divides the field plate structure into multiple segments: a first field plate in the first drift region and a second field plate in the second drift region. Each field plate is separated by a lightly-doped drift region, allowing the dielectric thickness between the field plate and adjacent p-n junction to be reduced while maintaining adequate voltage blocking through the combined effect of multiple segmented field plates and the lightly-doped region
Solution Approach 2:
The invention applies different doping levels to different regions: a lightly-doped drift region between the two heavily-doped drift regions. This local variation in doping quality allows the dielectric to be thinner while the lightly-doped region provides additional voltage blocking, thereby reducing on-state resistance without compromising reverse voltage blocking capability
2Object-affected harmful factors
If device cell pitch and field plate pitch are reduced to lower on-state resistance, then on-state resistance decreases, but field plate dielectric thickness must be reduced which adversely affects reverse voltage blocking capability
Solution Approach 1:
By segmenting the field plate structure into multiple field plates separated by lightly-doped drift regions, the invention enables reduced field plate pitch and thinner dielectric thickness while maintaining reverse voltage blocking capability through the cumulative effect of multiple segmented field plates and the lightly-doped drift region
Solution Approach 2:
The lightly-doped drift region positioned between heavily-doped drift regions provides enhanced voltage blocking in localized areas, allowing the overall field plate pitch to be reduced and dielectric to be thinner while maintaining adequate reverse voltage blocking capability
3Reliability
If field plates are formed in the same trench as gate electrode, then reverse voltage blocking is improved, but manufacturing complexity and cost increase due to alignment requirements
Solution Approach 1:
The invention extracts the field plate structure from the gate trench and places it in a separate, independent trench. This separation removes the alignment dependency between field plates and gate electrodes, simplifying manufacturing while maintaining the voltage blocking function through the independent field plate configuration with lightly-doped drift region
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 approach results in a power semiconductor device with significantly reduced on-state resistance (RDSon) while maintaining high reverse voltage blocking capability, achieved by using thinner insulation materials and independent field electrode pitch, leading to improved switching speed and cost-effectiveness.
Implementation Method 1
a dielectric lining an inner peripheral surface of the trench and disposed between the field electrode and the drift region
Implementation Method 2
to allow a depletion region expand in the drift region
Data Source
AI summary
A power semiconductor device is disclosed. The power semiconductor device includes an upper drift region situated over a lower drift region, a field electrode embedded in the lower drift region, the field electrode not being directly aligned with a gate trench in a body region of the power semiconductor device, where respective top surfaces of the field electrode and the lower drift region are substantially co-planar. A conductive filler in the field electrode can be substantially uniformly doped, and the field electrode is in direct electrical contact with the upper drift region.