Vertical Bismuth Transistor Channel Structure for Contact Resistance Reduction
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Solution Overview
Problem
Transistors with a vertically arranged channel structure made of semimetal materials like bismuth face challenges in reducing contact resistances with source and drain regions, which affects their performance.
Innovation Solution
A method involving the formation of a stack with specific contact and gate layers, creation of holes with varying cross-sections, filling with bismuth-based materials, and recrystallization to form semiconductor channel and conductive source/drain regions, along with the use of insulating and noble metal materials to optimize contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a vertically arranged channel structure made of semimetal materials is used, then the transistor performance is improved, but the contact resistance with source and drain regions increases
Solution Approach 1:
The patent applies local quality by creating regions with different cross-sectional dimensions within the same continuous material structure. The channel region has a smaller cross-section optimized for semiconductor behavior, while the source and drain regions have larger cross-sections optimized for conductive behavior. This spatial variation in dimensions allows different functional properties to be achieved in different locations of the same material, resolving the contradiction between transistor performance and contact resistance.
Solution Approach 2:
The patent utilizes parameter changes by varying the cross-sectional dimension of the material structure along its length. By changing the dimensional parameter from small (in the channel region) to large (in the source and drain regions), the electrical properties transition from semiconductor to conductive behavior. This parameter variation enables the same material to fulfill multiple functional requirements, addressing both transistor performance and contact resistance issues.
2Reliability
If the channel cross-section is reduced below a threshold value to achieve semiconductor behavior, then the material exhibits semiconductor properties, but the source and drain regions require larger cross-sections for good conductivity
Solution Approach 1:
The patent applies segmentation by dividing the continuous material structure into functionally distinct regions: a channel region with smaller cross-section for semiconductor behavior, and source/drain regions with larger cross-sections for conductive behavior. Although the material itself is continuous, the structural segmentation into regions with different dimensions enables different electrical functions, resolving the contradiction between semiconductor properties and conductivity requirements.
Solution Approach 2:
The patent implements local quality by assigning different cross-sectional dimensions to different spatial locations within the material structure. The channel region is locally optimized with a smaller cross-section to achieve semiconductor properties, while the source and drain regions are locally optimized with larger cross-sections to ensure good conductivity. This localized optimization allows each region to fulfill its specific functional requirement.
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 reduces contact resistances and enhances the performance of transistors by creating regions with tailored dimensions and properties, improving conductivity and reducing electron reflection effects.
Implementation Method 1
Such a material has the advantage of exhibiting the properties of a semiconductor or of a conductive material depending on its dimensions.
Implementation Method 2
the hole is made so as to have a first portion and a second portion located in the first layer and in the second layer respectively, each having a cross-section that is greater than that of a third portion of the hole located in the gate block
Implementation Method 3
The given bismuth-based material may be polycrystalline at the time it is deposited. Then, after filling, a recrystallisation annealing step is carried out in order to give it a monocrystalline constitution.
Data Source
AI summary
A vertical channel transistor comprising:a structure made of a given bismuth-based material which passes through a gate block where the structure comprises a channel region which extends through the gate block and source and drain regions on either side of the channel region and of the gate block, where the source and drain regions have a cross-section which is greater than the cross-section of the channel region (FIG. 1K).