Transistor Breakdown Voltage via Segmented Doping
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Solution Overview
Problem
Conventional transistors have relatively low breakdown voltages, limiting their operational voltage conditions and requiring separate high-voltage processes that increase manufacturing costs and yield issues.
Innovation Solution
The structure of transistors is modified by forming a heavily doped region adjacent to the well and using a plug of highly doped material extending from the metallic contact, which inhibits potential differences and reduces current crowding, allowing for higher breakdown voltages without additional processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transistor structures are used, then manufacturing processes are simple and costs are low, but breakdown voltage is limited to nominal process voltage levels
Solution Approach 1:
The transistor structure is segmented into distinct doped regions: a first doped region at the source/drain contact, a second doped region in the channel, and a third doped region at the opposite contact. This segmentation allows each region to be optimized for its specific function, with the lightly-doped second region extending the breakdown voltage while the heavily-doped first and third regions maintain low contact resistance.
Solution Approach 2:
Different doping concentrations are applied locally to different regions of the transistor. The first and third doped regions have high doping concentrations (e.g., 1e19 to 1e21 atoms/cm³) to ensure low contact resistance, while the second doped region has a lower doping concentration (e.g., 1e16 to 1e18 atoms/cm³) to extend the depletion region and increase breakdown voltage. This local quality variation resolves the contradiction between low resistance and high breakdown voltage.
2Reliability
If separate high voltage processes are used to form high voltage transistors, then breakdown voltage is improved, but manufacturing cost increases and yield decreases
Solution Approach 1:
The invention enables a single low-voltage manufacturing process to produce transistors with high breakdown voltage characteristics. By carefully controlling the doping profiles and geometric dimensions within a standard process, the same fabrication line can produce both low-voltage and high-voltage transistors, eliminating the need for separate high-voltage process lines and associated yield penalties.
Solution Approach 2:
The breakdown voltage is enhanced by changing key parameters within the existing process: extending the length of the lightly-doped second region, optimizing the doping concentration gradient, and adjusting the depth of the doped regions. These parameter changes allow high breakdown voltage to be achieved using standard low-voltage process equipment and materials.
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 enables transistors to achieve breakdown voltages significantly higher than expected, up to three times the nominal process voltage, while maintaining device performance and reducing manufacturing costs by using existing low-voltage processes.
Implementation Method 1
a relatively heavily doped region is formed adjacent or in the bottom of a well defining the transistor. This can help to inhibit potential differences between the source, drain or gate, and the substrate beneath and around the well forming a depletion region within the well of material.
Implementation Method 2
at least the drain, and optionally the source, has a plug of relatively highly doped material extending from a region of contact with a metallic conductor. This can reduce current crowding near the surface of the device.
Data Source
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AI summary
Transistors having improved breakdown voltages and methods of forming the same are provided herein. In one embodiment, a method of forming a transistor comprises the steps of: forming a drain (10) and a source (8) by doping a semiconductor with a first dopant type to form a first type of semiconductor, the drain and source being separated from one another, wherein the drain comprises a first drain region (202) of a first dopant concentration adjacent a second drain region (204), such that at least a portion of the second drain region is positioned between the first drain region and the source, and further comprising forming an intermediate region (200) by doping the semiconductor so as to form a second type of semiconductor intermediate the drain and source, the intermediate region spaced apart from the second drain region.