High Voltage MOS Device With Buried Columns
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Solution Overview
Problem
High voltage MOS devices face a trade-off between breakdown voltage and on-resistance, where increasing breakdown voltage leads to higher on-resistance and vice versa, limiting their performance and application range.
Innovation Solution
The design incorporates a well region, a drift region, a gate, a source, and buried columns with a predetermined distance from the surface, allowing for a super junction formation under reverse bias to enhance breakdown voltage without increasing on-resistance by ensuring the buried columns do not contact the top surface, maintaining low on-resistance during operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the breakdown voltage is increased in high voltage MOS devices, then the device can withstand higher voltages, but the on-resistance increases which degrades device performance
Solution Approach 1:
The drift region is segmented into multiple regions with different doping concentrations (first drift region with higher doping near the channel, second drift region with lower doping deeper in the substrate). This segmentation allows the device to achieve high breakdown voltage through the low-doping region while maintaining low on-resistance through the high-doping region near the channel.
Solution Approach 2:
Different regions of the drift zone are assigned different doping concentrations to fulfill different functions: the first drift region has higher doping concentration to reduce on-resistance where current flows, while the second drift region has lower doping concentration to increase breakdown voltage where the electric field is strongest during reverse bias.
2Reliability
If the drift region is extended deeper into the substrate to increase breakdown voltage, then higher voltage tolerance is achieved, but the manufacturing complexity and cost increase
Solution Approach 1:
The well region and drift region are formed with predetermined doping concentrations and depths before final device assembly. The first drift region is formed with higher doping concentration at a controlled depth, and the second drift region is formed with lower doping concentration extending deeper, establishing the voltage-blocking structure in advance to simplify subsequent manufacturing steps.
3Object-generated harmful factors
If the doping concentration in the drift region is increased to reduce on-resistance, then conduction losses are reduced, but the breakdown voltage decreases
Solution Approach 1:
The drift region is divided into two segments with different doping concentrations: the first drift region closer to the channel has higher doping concentration to reduce on-resistance and conduction losses, while the second drift region extending deeper has lower doping concentration to provide high breakdown voltage capability through enhanced electric field distribution.
Solution Approach 2:
The doping concentration is optimized locally at different depths within the drift region. The upper portion (first drift region) has higher doping to minimize resistive losses during conduction, while the lower portion (second drift region) has lower doping to maximize voltage blocking capability during reverse bias operation.
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 the breakdown voltage of high voltage MOS devices without sacrificing on-resistance, thereby improving device performance and expanding its application range while maintaining low conduction current during ON operation.
Implementation Method 1
when a reverse bias voltage is applied between the well region and the drift region, a super junction can be generated by the depletion effect of two adjacent buried columns and the drift region in between
Implementation Method 2
a super junction can be generated by the depletion effect of two adjacent buried columns and the drift region in between, so as to increase the breakdown voltage of the high voltage MOS device
Data Source
AI summary
A high voltage MOS device includes: a well, a drift region, a gate, a source, a drain, and plural buried columns. A part of the gate is stacked on a part of the well, and another part of the gate is stacked on a part of the drift region. The source connects the well in a lateral direction. The drain connects the drift region in the lateral direction. The drain and the source are separated by the well and the drift region, and the drain and the source are located at different sides of the gate. The plural buried columns are formed beneath the top surface by a predetermined distance, and each buried column does not connect the top surface. At least a part of every buried column is surrounded by the drift region, and the buried columns and the drift region are arranged in an alternating manner.