Power Semiconductor Edge Termination with Field Limiting Rings
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Solution Overview
Problem
Existing edge termination techniques for high voltage semiconductor devices, such as MOSFETs and IGBTs, fail to effectively reduce the electric field at the junction of the active area and the junction termination extension (JTE) region, leading to lower breakdown voltages due to the curvature of the cylindrical junction, which results in potential arcing or avalanche breakdown.
Innovation Solution
A semiconductor device design incorporating a doped semiconductor substrate with an upper layer featuring a well region and a JTE region, supplemented by field limiting rings of varying dopant density, which extend away from the well region and form a variation of lateral doping (VLD) structure, thereby reducing the electric field and increasing breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cylindrical junction structure is used in high voltage semiconductor devices, then the device can be manufactured using standard planar diffusion techniques, but the curvature at the edge of the junction produces a greater electric field leading to lower breakdown voltage
Solution Approach 1:
The device structure is segmented into distinct regions: an active region with a well, a junction termination extension (JTE) region, and field limiting rings. This segmentation allows each region to be optimized independently - the active region for device functionality and the termination regions for electric field management, thereby maintaining manufacturability while improving breakdown voltage.
Solution Approach 2:
The patent applies local quality by creating regions with different doping concentrations and structures at specific locations. The JTE region has varying dopant density (higher near the well, lower at the edge) and the field limiting rings are strategically positioned to provide localized electric field control exactly where the cylindrical junction curvature causes problems, without affecting the overall device manufacturability.
2Reliability
If field limiting rings are added to the JTE region, then the breakdown voltage increases by compensating the curved junction's electric field influence, but the device structure and manufacturing process become more complex
Solution Approach 1:
The field limiting rings are merged with the JTE region structure, forming an integrated edge termination system. Both features are created using the same planar diffusion process sequence, combining multiple functions (electric field management, breakdown voltage enhancement) into a unified structure that can be manufactured in a single process flow, thereby limiting the increase in device complexity.
Solution Approach 2:
The patent utilizes parameter changes by varying the dopant density in the JTE region (creating a gradient from higher concentration near the well to lower at the edge) and by adjusting the doping parameters of the field limiting rings. These parameter variations are achieved through controlled diffusion processes, allowing precise electric field management without requiring additional complex manufacturing steps.
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 implementation of field limiting rings within the JTE region enhances the breakdown voltage by compensating the curved junction's electric field influence, even under high leakage current densities, effectively preventing arcing and avalanche breakdown, as demonstrated by improved current-voltage characteristics.
Implementation Method 1
the curvature at the edge of the junction it produces a greater electric field than an ideal planar junction
Implementation Method 2
avalanche breakdown within the substrate near its surface
Implementation Method 3
The JTE region is of varying dopant density, the dopant density being maximum at the point beneath the junction at the upper surface of the upper layer of the JTE region with the well region. The dopant density of the JTE region decreases in both lateral directions from its maximum point.
Data Source
AI summary
A semiconductor device has a heavily doped substrate and an upper layer with doped silicon of a first conductivity type disposed on the substrate, the upper layer having an upper surface and including an active region that comprises a well region of a second, opposite conductivity type. An edge termination zone has a junction termination extension (JTE) region of the second conductivity type, the region having portions extending away from the well region and a number of field limiting rings of the second conductivity type disposed at the upper surface in the junction termination extension region.