Superjunction MOSFET Drift Structure for RF Resonance Stability
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Solution Overview
Problem
Superjunction power MOS devices face challenges in radio-frequency applications due to parasitic components that prevent operation at desired resonance frequencies, resulting in subharmonic operation instead of the intended frequency, caused by an inflection region in the output capacitance plot.
Innovation Solution
The introduction of an interruption portion in the drift region between the first and second columns of the superjunction power MOS device, and the use of intermediate regions between the first columns and body regions, to achieve a more uniform output capacitance plot and improved breakdown voltage, allowing for better high-frequency behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a superjunction structure with first and second columns is used, then breakdown voltage is improved, but output capacitance exhibits an inflection region causing subharmonic operation at desired resonance frequencies
Solution Approach 1:
The drift region is segmented into multiple regions (first drift region, second drift region, and interruption portion) with different doping concentrations and structures. This segmentation modifies the electric field distribution to eliminate the inflection region in the output capacitance plot, enabling reliable operation at the desired resonance frequency while maintaining high breakdown voltage through the superjunction column structure.
2Strength
If the epitaxial layer thickness and resistivity are optimized for breakdown voltage, then breakdown voltage is improved, but on-resistance cannot be independently optimized
Solution Approach 1:
The drift region is divided into multiple segments with different doping characteristics. The first drift region has higher doping concentration for low on-resistance, while the second drift region has lower doping concentration for high breakdown voltage. This segmentation allows independent optimization of both parameters without compromising either performance metric.
Solution Approach 2:
Different regions of the drift region are assigned different local properties (doping concentrations) to fulfill different functions. The first drift region provides low resistance for current conduction, while the second drift region provides high breakdown voltage capability. This local differentiation enables simultaneous optimization of both parameters.
3Ease of manufacture
If body regions extend to the top ends of the first columns, then manufacturing is simplified, but output capacitance uniformity deteriorates
Solution Approach 1:
The drift region is segmented to include an interruption portion that prevents body regions from extending to the top ends of the first columns. This segmentation creates a discontinuity that improves output capacitance uniformity by eliminating the parasitic capacitance effects at the column-top interfaces, while the overall manufacturing process remains compatible with standard semiconductor fabrication techniques.
Data Source
AI summary
A semiconductor MOS device having an epitaxial layer with a first conductivity type formed by a drain region and by a drift region. The drift region accommodates a plurality of first columns with a second conductivity type and a plurality of second columns with the first conductivity type, the first and second columns alternating with each other and extending on the drain region. Insulated gate regions are each arranged on top of a respective second column; body regions having the second conductivity type extend above and at a distance from a respective first column, thus improving the output capacitance Cds of the device, for use in high efficiency RF applications.