Body Connection Lines for Vertical Transistors
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Solution Overview
Problem
Floating body effects in vertical access transistors lead to degraded charge retention and power distribution issues in memory arrays, necessitating the development of architectures that alleviate these effects.
Innovation Solution
The implementation of body connection lines that electrically couple the body regions of vertical access devices to a reference voltage, using a different composition than the semiconductor material, such as polycrystalline silicon for the connection lines and monocrystalline silicon for the pillars, with lateral edges penetrating into the pillars, to stabilize the channel region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If vertical access devices are used in memory cells, then device footprint is reduced and integration density is improved, but floating body effects occur causing degraded charge retention and power distribution problems
Solution Approach 1:
An intermediate body contact structure is introduced between the floating body region and the reference voltage potential. This contact structure includes a body contact region extending from a first level to a second level, with a body contact conductor coupling the body contact region to reference voltage, thereby mediating the electrical connection and eliminating floating body effects while preserving the vertical device architecture
Solution Approach 2:
The body contact structure extends vertically through multiple levels (from first level to second level) within the semiconductor structure, utilizing the vertical dimension to establish electrical connection. This dimensional approach allows the body contact to reach the floating body region without interfering with the planar footprint of the vertical access device
2Productivity
If vertical access devices are used in memory cells, then integration density is improved, but power distribution problems arise due to floating body effects
Solution Approach 1:
The body contact conductor acts as an intermediary that provides a dedicated electrical pathway for power distribution to the body region. By coupling the body contact region to reference voltage potential, it ensures stable power supply and eliminates the power distribution problems associated with floating body effects in high-density vertical device architectures
3Ease of manufacture
If the body region is left floating in vertical access devices, then device fabrication is simplified, but charge retention is degraded
Solution Approach 1:
The body contact structure is extracted as a separate, independently formed element that can be added during standard fabrication processes. The body contact region and body contact conductor are formed as distinct structures that can be integrated without fundamentally changing the fabrication workflow, thus maintaining ease of manufacture while eliminating floating body effects
Data Source
AI summary
Some embodiments include an apparatus having a transistor associated with a vertically-extending semiconductor pillar. The transistor includes an upper source/drain region within the vertically-extending semiconductor pillar, a lower source/drain region within the vertically-extending semiconductor pillar, and a channel region within the vertically-extending semiconductor pillar and between the upper and lower source/drain regions. The transistor also includes a gate along the channel region. A wordline is coupled with the gate of the transistor. A digit line is coupled with the lower source/drain region of the transistor. A programmable device is coupled with the upper source/drain region of the transistor. A body connection line is over the wordline and extends parallel to the wordline. The body connection line has a lateral edge that penetrates into the vertically-extending semiconductor material pillar. The body connection line is of a different composition than the semiconductor material pillar.