Trench Field Plate MOSFET Termination With Floating Body Segments
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Solution Overview
Problem
Trench field plate power MOSFETs face limitations in achieving optimal breakdown voltage due to sensitivity to doping and dimension variations, and improper termination structures can lead to low breakdown voltage, making it challenging to achieve the desired tradeoff between breakdown voltage and on-resistance.
Innovation Solution
The implementation of floating body segments between device trenches, which self-bias to a positive voltage, effectively suppresses the electric field at triple-point regions, isolating the active body area from the termination area and preventing breakdown voltage roll-off, and are formed using the same body implant/diffusion process as the active body area to enhance fabrication efficiency and cost savings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RESURF action is employed with field plates in gate trenches, then breakdown voltage is improved and on resistance is reduced, but sensitivity to variations in doping and dimensions is greatly increased
Solution Approach 1:
The body area is segmented into multiple isolated body segments by introducing trench structures. Each body segment is separated by trenches filled with dielectric material, creating electrically isolated regions. This segmentation reduces the sensitivity to doping and dimension variations by distributing the electric field across multiple smaller segments rather than one large continuous body area.
Solution Approach 2:
Trench structures filled with dielectric material are introduced as intermediary elements between the body segments. These trenches act as mediators that isolate the body segments electrically while maintaining structural integrity. The dielectric material in the trenches provides electrical insulation and helps control the electric field distribution, reducing sensitivity to variations in doping and dimensions.
2Reliability
If termination structures are improperly designed, then breakdown voltage becomes low, but device complexity increases to achieve optimal BV-RDS(on) tradeoff
Solution Approach 1:
The termination region is segmented into multiple isolated body segments using trench structures. This segmentation simplifies the termination design by creating discrete, manageable units rather than requiring complex continuous termination structures. Each segment can be independently optimized, reducing overall device complexity while maintaining high breakdown voltage.
Solution Approach 2:
The solution moves from planar termination structures to three-dimensional trench-based termination. By introducing vertical trenches filled with dielectric material, the termination design gains an additional dimensional degree of freedom. This allows for simpler two-dimensional layout patterns to achieve the same or better breakdown voltage performance, reducing device complexity.
3Reliability
If floating body segments are introduced to suppress electric field at triple-point regions, then breakdown voltage increases, but device complexity increases
Solution Approach 1:
The body area is divided into multiple isolated body segments separated by trenches. This segmentation naturally creates the floating body segment structure needed to suppress electric field at triple-point regions. The segmentation approach achieves the desired electric field control while maintaining a relatively simple and scalable device architecture.
Solution Approach 2:
The trench structures serve multiple functions simultaneously: they isolate body segments electrically, provide mechanical support, control electric field distribution, and define active regions. This multi-functionality reduces the need for additional specialized structures, thereby limiting the increase in device complexity while achieving breakdown voltage enhancement.
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 increases the breakdown voltage by suppressing electric field enhancements at triple-point regions, allowing for a better breakdown voltage - lower on-resistance tradeoff and providing a wider design and process margin, even for high epitaxial layer doping and wide trench spacing scenarios.
Implementation Method 1
floating body segments between device trenches of the MOSFET that self-bias to a positive voltage
Implementation Method 2
effectively suppresses the electric field at triple-point regions
Implementation Method 3
typically employs reduced surface field (RESURF) action under the influence of field plates (shield electrodes) inside gate trenches
Data Source
Figure 1
Figure 2~4
Figure 5
AI summary
A semiconductor device includes a substrate having opposed first and second major surface, an active area, and a termination area. Insulated trenches extend from the first major surface toward the second major surface, each of the insulated trenches including a conductive field plate and a gate electrode overlying the conductive field plate, the gate electrode being separated from the field plate by a gate-field plate insulator. The field plate extends longitudinally in both of the active and termination areas and the gate electrode is absent in the termination area. A body region of a first conductivity type extends laterally between pairs of the insulated trenches. First and second spacer regions of a second conductivity type extend laterally between the pairs of the insulated trenches at the termination area to produce segments of the first conductivity type between the first and second spacer regions that are isolated from the body region.