SiC Guard Ring Impurity Gradient for Avalanche Reliability
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Solution Overview
Problem
SiC semiconductor devices face issues with current concentration at the terminal end portion during avalanche breakdown, leading to device destruction, despite measures to enhance breakdown voltage.
Innovation Solution
A SiC semiconductor device with a guard ring having a second-conductivity-type impurity concentration smaller than the first-conductivity-type impurity concentration in the surface layer portion, dispersing current density and reducing electric field concentration, thereby preventing device destruction during avalanche breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a p-type guard ring is formed in the SiC semiconductor layer to make contact with the terminal end portion of the Schottky electrode, then breakdown voltage is improved by broadening the depletion layer, but current concentration occurs at the terminal end portion during avalanche breakdown
Solution Approach 1:
The guard ring structure implements local quality by creating a non-uniform impurity concentration distribution within the guard ring region. The surface layer portion has a lower second-conductivity-type impurity concentration compared to the bulk, resulting in different conductivity characteristics at different depths. This local variation in electrical properties allows the guard ring to simultaneously broaden the depletion layer for breakdown voltage enhancement while maintaining lower current density at the terminal end portion during avalanche breakdown, thereby improving anti-avalanche capacity.
2Reliability
If the second-conductivity-type impurity concentration in the guard ring surface layer is reduced, then current density is dispersed and anti-avalanche capacity is improved, but breakdown voltage enhancement may be compromised
Solution Approach 1:
The invention applies parameter changes by systematically varying the second-conductivity-type impurity concentration across different regions and depths of the guard ring. Specifically, the surface layer portion is designed with a lower impurity concentration than the bulk region, creating a depth-dependent concentration gradient. This parameter variation enables the guard ring to optimize both depletion layer broadening (through the overall guard ring structure) and current density dispersion (through the low-concentration surface layer), simultaneously achieving enhanced breakdown voltage and improved anti-avalanche capacity.
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 solution effectively reduces current density at the terminal end portion and enhances breakdown voltage by dispersing current density and broadening the depletion layer, preventing device destruction during avalanche breakdown.
Implementation Method 1
a depletion layer generated by a p-n junction is broadened near the terminal end portion of the Schottky electrode
Implementation Method 2
current concentration on the terminal end portion of the Schottky electrode may occur at the time of an avalanche breakdown of the device
Data Source
AI summary
A SiC semiconductor device includes a SiC semiconductor layer having a first-conductivity-type impurity, a field insulation film formed on a front surface of the SiC semiconductor layer and provided with an opening for exposing therethrough the front surface of the SiC semiconductor layer, an electrode connected to the SiC semiconductor layer through the opening of the field insulation film, and a guard ring having a second-conductivity-type impurity and being formed in a surface layer portion of the SiC semiconductor layer to make contact with a terminal end portion of the electrode connected to the SiC semiconductor layer. A second-conductivity-type impurity concentration in a surface layer portion of the guard ring making contact with the electrode is smaller than a first-conductivity-type impurity concentration in the SiC semiconductor layer.