Semiconductor Drain Offset Regions for Breakdown Voltage Trade-off
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Solution Overview
Problem
Conventional high voltage MOS transistors face a trade-off between static breakdown voltage and on-resistance, where increasing breakdown voltage leads to higher on-resistance due to the resistive nature of the electric-field limiting layer, and increasing impurity concentration in the N-type epitaxial layer reduces breakdown voltage.
Innovation Solution
The semiconductor device incorporates a structure with multiple drain offset regions of varying impurity concentrations, where the curvature portion of the body region is located in a region with lower impurity concentration, reducing the electric field strength at the PN junction, and increasing impurity concentration in other regions to lower on-resistance without decreasing breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electric-field limiting layer is formed in the drain region to increase static breakdown voltage, then breakdown voltage is improved, but on-resistance increases due to the resistive component
Solution Approach 1:
The patent applies local quality by creating three distinct drain offset regions (first, second, and third) with different impurity concentration profiles at different depths. The second drain offset region has lower impurity concentration to reduce electric field strength and increase breakdown voltage, while the first and third regions have higher impurity concentrations to reduce on-resistance. This spatial variation in material properties resolves the contradiction between breakdown voltage and on-resistance.
Solution Approach 2:
The drain offset region is segmented into three separate regions with different impurity concentrations. The first drain offset region (higher impurity concentration) suppresses parasitic transistors, the second drain offset region (lower impurity concentration) increases breakdown voltage by reducing electric field strength at the curvature portion, and the third drain offset region (higher impurity concentration) reduces on-resistance. This segmentation allows each region to optimize for its specific function.
2Loss of energy
If impurity concentration in the N-type epitaxial layer is increased to reduce on-resistance, then on-resistance is improved, but breakdown voltage decreases
Solution Approach 1:
The patent implements local quality by establishing different impurity concentration levels in different vertical zones of the drain offset region. The second drain offset region maintains lower impurity concentration specifically where the curvature portion is located to preserve high breakdown voltage, while the first and third drain offset regions have higher impurity concentrations to reduce on-resistance. This localized differentiation resolves the contradiction.
Solution Approach 2:
The drain offset region is divided into three segments with distinct impurity concentrations. The first segment (first drain offset region) has higher impurity concentration for suppressing parasitic effects, the second segment (second drain offset region) has lower impurity concentration for high breakdown voltage, and the third segment (third drain offset region) has higher impurity concentration for low on-resistance. This segmentation enables simultaneous optimization of both parameters.
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 allows for increased static breakdown voltage while reducing on-resistance, effectively addressing the trade-off between the two parameters.
Implementation Method 1
an electric field strength in a curvature portion of the body region, that is, in a curvature portion of a PN junction
Implementation Method 2
an impurity concentration in the second drain offset region is lower than impurity concentrations in the first and third drain offset regions
Data Source
AI summary
In a semiconductor substrate of a first conductivity type, first to third drain offset regions of a second conductivity type are formed in that order in a bottom up manner. A body region of the first conductivity type is formed partly in the second drain offset region and partly in the third drain offset region. The second drain offset region has a lower impurity concentration than the first and third drain offset regions. A curvature portion of the body region is located in the second drain offset region.