Buffered Drain LDMOS Structure for Avalanche Ruggedness
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Solution Overview
Problem
Conventional LDMOS and drain extended transistor devices face challenges in maintaining ruggedness during transient events and avalanche breakdown while keeping specific on-resistance low, which is crucial for applications like switching DC-DC converters.
Innovation Solution
The semiconductor device design includes a first drift region, a drain region, and a LOCOS structure with a preserved tapered portion that serves as a screening oxide to allow shallow implantation dopants to form a buffer region between the drift and drain regions, improving doping concentration transition and enhancing safe-operating-area and ruggedness without increasing specific on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LDMOS or drain extended transistor design is used, then the device structure is simple and manufacturing is easier, but the device fails to maintain ruggedness during transient events and avalanche breakdown while keeping specific on-resistance low
Solution Approach 1:
The drift region is segmented into multiple regions with different dopant concentrations: a first drift region with lower dopant concentration adjacent to the channel, and a second drift region with higher dopant concentration adjacent to the drain. This segmentation allows optimization of both ruggedness and specific on-resistance by creating a gradual doping profile that reduces electric field peaks while maintaining low resistance.
Solution Approach 2:
Different regions of the drift region are assigned different dopant concentrations tailored to their specific functional requirements. The first drift region (lower doping) provides better breakdown characteristics and ruggedness, while the second drift region (higher doping) reduces specific on-resistance. This local quality differentiation resolves the contradiction by optimizing each region for its primary function.
2Reliability
If the dopant concentration in the drift region is increased to reduce specific on-resistance, then specific on-resistance decreases, but ruggedness during transient events and avalanche breakdown deteriorates
Solution Approach 1:
The drift region is divided into two segments with different dopant concentrations. The first drift region has lower dopant concentration (e.g., 1e16 to 1e17 atoms/cm³) to maintain high breakdown voltage and ruggedness, while the second drift region has higher dopant concentration (e.g., 1e17 to 1e18 atoms/cm³) to reduce specific on-resistance. This segmentation allows simultaneous optimization of both parameters.
Solution Approach 2:
The dopant concentration parameter is varied spatially across the drift region rather than being uniform. By changing the dopant concentration from lower in the first drift region to higher in the second drift region, the patent achieves both high ruggedness (from lower doping) and low specific on-resistance (from higher doping) in different locations.
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 design improves the safe-operating-area and ruggedness of the semiconductor devices, enabling them to survive load transients and negative current flow while maintaining or reducing specific on-resistance, thus ensuring device reliability and cost-effectiveness.
Implementation Method 1
allow shallow implantation dopants to form a buffer region between the drift and drain regions
Implementation Method 2
An oxide structure is between the channel region and the drain region
Data Source
AI summary
A semiconductor device includes a source region. A drain region has a first conductivity type and a second dopant concentration spaced apart from the source region. A first drift region is located between the source region and the drain region and has the first conductivity type and a first dopant concentration that is lower than the second dopant concentration of the drain region. An oxide structure includes a first portion on or over the first drift region and a tapered portion between the first portion and the drain region. A substrate surface extension is between the tapered portion and the drain region. A buffer region has the first conductivity type between the first drift region and the drain region and under the tapered portion of the oxide structure. The buffer region has a third dopant concentration between the second dopant concentration and the first dopant concentration.