Transistor Avalanche Bypass Structure for Breakdown Protection
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Solution Overview
Problem
Transistors, particularly MOSFETs, face degradation and potential avalanche breakdown when subjected to high voltages, leading to reduced voltage blocking capability and increased on-resistance due to hot charge carriers in the field electrode dielectric.
Innovation Solution
Incorporating an avalanche bypass structure between the source and drain electrodes, comprising semiconductor layers with varying doping concentrations and a pn-junction, which bypasses the drift region before avalanche breakdown occurs, thereby preventing damage and maintaining voltage blocking capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the transistor is designed to withstand high voltages, then the voltage blocking capability is improved, but avalanche breakdown occurs at the pn-junction leading to degradation
Solution Approach 1:
An avalanche bypass structure is introduced as an intermediary element between the source and drain regions. This structure includes a first doped region with lower doping concentration and a second doped region with higher doping concentration, forming a pn-junction that provides an alternative current path during avalanche conditions, protecting the main transistor pn-junction from breakdown
Solution Approach 2:
The avalanche bypass structure utilizes controlled doping concentration parameters, with the first doped region having a lower doping concentration than the second doped region. This parameter variation creates optimal electric field distribution that enables the bypass structure to activate at controlled voltage levels, preventing unwanted avalanche breakdown in the main transistor
2Strength
If high voltage is applied to the transistor in off-state, then the voltage blocking capability is tested, but hot charge carriers are generated in the field electrode dielectric increasing on-resistance
Solution Approach 1:
The avalanche bypass structure extracts or diverts the harmful hot charge carriers away from the main transistor channel and field electrode dielectric. By providing an alternative current path through the bypass pn-junction, the structure prevents charge carrier injection into the dielectric, thereby eliminating the source of hot charge carriers that would otherwise increase on-resistance
3Duration of action of stationary object
If the transistor operates under repetitive avalanche conditions, then the voltage blocking capability should be maintained, but degradation effects occur
Solution Approach 1:
The avalanche bypass structure serves as a protective cushion that activates before the main transistor pn-junction undergoes damaging avalanche breakdown. By providing a controlled breakdown path in the bypass structure with its specifically designed doping profile, the system prevents repetitive stress from degrading the main transistor, enabling sustained operation under high voltage conditions
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 avalanche bypass structure effectively prevents avalanche breakdown at the pn-junction, reducing on-resistance and ensuring repetitive high-voltage withstand capability without degradation.
Implementation Method 1
When, in the off-state, a voltage with a level higher than this maximum voltage level is applied to the transistor an avalanche breakthrough may occur at an internal pn-junction of the transistor
Data Source
AI summary
A transistor cell includes a drift region, a source region, a body region, and a drain region that is laterally spaced apart from the source region. A gate electrode is adjacent the body region. A field electrode is arranged in the drift region. A source electrode is connected to the source region and the body region, and a drain electrode is connected to the drain region. An avalanche bypass structure is coupled between the source electrode and the drain electrode and includes a first semiconductor layer of the first doping type, a second semiconductor layer of the first doping type, and a pn-junction arranged between the first semiconductor layer and the source electrode. The second semiconductor layer has a higher doping concentration than the first semiconductor layer and is arranged between the second semiconductor layer and the drift region. The drain electrode is electrically connected to the second semiconductor layer.