Edge Termination Using Permanent Charge in High-Voltage Semiconductors
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Solution Overview
Problem
High-voltage semiconductor devices face challenges in edge termination structures, as conventional methods are precluded by the presence of thick P layers, leading to potential breakdown and increased risk of conductive failure due to high electric fields.
Innovation Solution
The implementation of lateral out-diffusion to create p-type drift regions and a junction surrounding the active area, allowing the use of n-type epitaxial material for edge termination, which reduces peak electric fields and enables the use of conventional termination structures like Field Plates and Guard Rings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional termination structures are used, then edge termination is provided, but breakdown occurs due to high electric fields caused by thick P layers
Solution Approach 1:
The patent changes the conductivity type parameter of the epitaxial layer from p-type to n-type, and introduces permanent positive charges in the termination region. This parameter change allows the use of conventional termination structures while reducing peak electric fields and preventing breakdown in high-voltage devices with thick P layers.
Solution Approach 2:
The patent introduces permanent positive charges as an intermediary element in the termination region. These charges act as a mediator to reduce the peak electric field at the edge termination, enabling conventional termination structures to function effectively despite the presence of thick P layers.
2Adaptability or versatility
If thick P layers are used for active devices, then device functionality is achieved, but conventional termination structures cannot be used
Solution Approach 1:
By changing the epitaxial layer conductivity to n-type and introducing permanent positive charges, the patent enables compatibility with conventional termination structures (Field Plates, Guard Rings, JTE) that would otherwise be incompatible with thick P layer configurations.
3Reliability
If larger termination area is provided, then breakdown voltage is improved, but device area increases
Solution Approach 1:
The patent achieves high breakdown voltage with reduced termination area by changing the conductivity type to n-type and introducing permanent positive charges, which reduce peak electric fields and allow more efficient use of the termination region.
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 results in a smaller area requirement for termination, reduced likelihood of breakdown in the peripheral area, and the ability to form termination structures simultaneously with the active area, enhancing the reliability of high-voltage semiconductor devices.
Implementation Method 1
Under reverse bias the depletion zone at the junction 120/130 will spread mainly into p type layer 120
Implementation Method 2
the electric field does not get high enough to cause breakdown at the rated operating voltage
Implementation Method 3
Lateral out-diffusion from the trenches provides first-type (e.g. p-type) drift regions for the active devices
Data Source
AI summary
An edge termination structure includes a final dielectric trench containing permanent charge. The final dielectric trench is surrounded by first conductivity type semiconductor material (doped by lateral outdiffusion from the trenches), which in turn is laterally surrounded by second conductivity type semiconductor material.