Semiconductor Vertical Drift and Edge Termination Design
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Solution Overview
Problem
Existing semiconductor devices face a trade-off between on-state resistance and breakdown voltage, with superjunction structures attempting to mitigate this through parallel p-n structures, but these designs often lead to increased leakage current and thermal runaway due to shortened carrier lifetimes in edge termination regions.
Innovation Solution
A semiconductor device with a vertical drift portion forming a first parallel p-n structure and an edge termination region forming a second parallel p-n structure, where the impurity concentration of the second conductivity type low resistance layer is higher than the first, and a p+ type drain region is selectively provided within the n+ type drain layer in the edge termination region to suppress carrier injection, thereby reducing the accumulation of carriers and enhancing breakdown withstand.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the n-type drift layer is made thinner to reduce on-state resistance, then on-state resistance decreases, but breakdown voltage drops due to reduced depletion layer spread
Solution Approach 1:
The drift layer is segmented into multiple alternating n-type and p-type columns forming a parallel p-n structure. This segmentation allows the depletion region to extend laterally across multiple junctions during off-state, effectively increasing the breakdown voltage path length without increasing the physical thickness of the drift layer, thereby maintaining low on-state resistance while achieving high breakdown voltage.
Solution Approach 2:
The patent transitions from a one-dimensional vertical current path to a two-dimensional depletion region spread by creating parallel p-n columns. The depletion region extends laterally in the horizontal dimension across multiple alternating columns, allowing breakdown voltage to be determined by lateral spread rather than vertical thickness, thus decoupling the trade-off between on-state resistance and breakdown voltage.
2Reliability
If the carrier lifetime in edge termination region is shortened to increase breakdown withstand, then breakdown withstand increases, but leakage current increases due to reduced carrier recombination control
Solution Approach 1:
The patent applies different impurity concentrations locally: the edge termination region has higher p-type impurity concentration than the active region, creating a localized high-field region. This local quality difference allows the edge termination to withstand higher breakdown voltages while the active region maintains proper carrier recombination characteristics, preventing excessive leakage current.
Solution Approach 2:
The patent changes the impurity concentration parameter in the edge termination region, making it higher than in the active region. This parameter change creates a controlled high-field region that enhances breakdown withstand capability while the specific concentration values are optimized to prevent excessive leakage current by balancing carrier generation and recombination.
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 configuration effectively increases breakdown withstand capability while minimizing leakage current and reducing loss by reducing carrier accumulation in the edge termination region, thus balancing on-state resistance and breakdown voltage.
Implementation Method 1
a portion of the high-resistance n− type drift layer depletes when in an off-state, increasing breakdown voltage
Implementation Method 2
a depletion layer spreads laterally from each vertically extending p-n junction of the parallel p-n structure when in an off-state, depleting the whole of the drift layer
Data Source
AI summary
A drain drift portion is a first parallel p-n structure, largely corresponding to a portion directly below a p-type base region forming an active region, formed by first n-type regions and first p-type regions being alternately and repeatedly joined. The periphery of the drain drift portion is an edge termination region formed of a second parallel p-n structure aligned contiguously to the first parallel p-n structure and formed by second n-type regions and second p-type regions being alternately and repeatedly joined. An n-type buffer layer is provided between the first and second parallel p-n structures and an n+ type drain layer. A p+ type drain region is selectively provided inside the n+ type drain layer in the edge termination region, penetrating the n+ type drain layer in the depth direction.