Nanotubular MOSFET Inner Outer Gate Segmentation
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Solution Overview
Problem
Silicon-based metal oxide semiconductor field effect transistors (MOSFETs) face challenges such as the 'floating body effect' leading to inconsistent device operation, increased leakage current, and self-heating issues due to high current flow, which affect performance and threshold voltage control, especially in applications like SRAM cells and logic gates.
Innovation Solution
A nanotubular MOSFET structure is developed with an inner and outer gate configuration, utilizing reactive ion-etching and selective etching to form a tubular silicon-on-silicon configuration, where the inner and outer gates can operate with the same or opposite polarity to reduce the floating body effect and enhance channel control, and self-alignment techniques are used to grow silicon epitaxially and form silicided gates and contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If SOI MOSFET technology is used to enhance device performance, then on current increases and parasitic capacitance decreases, but floating body effect causes inconsistent device operation and threshold voltage control
Solution Approach 1:
The invention divides the single gate structure into multiple gates (first gate and second gate) positioned at different locations around the nanotube channel. This segmentation allows independent control of channel regions, enabling suppression of floating body effects while maintaining high on current performance.
Solution Approach 2:
The nanotube structure acts as an intermediary between the gates and the channel, providing superior electrostatic control compared to conventional planar structures. The nanotube geometry enables all-around gate control, eliminating the floating body effect that plagues SOI MOSFETs.
2Object-affected harmful factors
If SOI MOSFET is used, then parasitic capacitance between body and other components is reduced, but floating body charge storage causes dynamic sub-threshold leakage and threshold voltage mismatch
Solution Approach 1:
By segmenting the gate into multiple independently controllable gates, the invention prevents charge accumulation in the body region. Each gate can be adjusted to maintain proper potential distribution, eliminating the charge storage effect that causes leakage and threshold voltage mismatch.
Solution Approach 2:
The invention changes the electrical parameters by applying different voltages to the first and second gates, enabling dynamic control of the channel potential. This parameter adjustment prevents floating body charge accumulation and eliminates sub-threshold leakage.
3Productivity
If conventional MOSFET scaling continues, then device density increases, but quantum mechanical effects and stochastic material properties cause performance degradation
Solution Approach 1:
The invention transitions from two-dimensional planar MOSFET scaling to a three-dimensional nanotube structure with gates positioned around the channel. This dimensional change provides superior electrostatic control and immunity to quantum mechanical effects while maintaining high device density.
Solution Approach 2:
The invention employs composite material structures combining nanotube semiconductor material with multiple gate electrodes and insulating layers. This composite structure provides both the density benefits of scaling and the reliability benefits of enhanced electrostatic control.
4Power
If high current flow is used to improve device performance, then on current increases, but self-heating due to I2R law degrades carrier mobility and drive current
Solution Approach 1:
The segmented gate structure enables localized control of current flow, distributing the current density more evenly across the channel. This reduces hot spots and self-heating effects while maintaining high overall drive current capability.
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
The nanotubular MOSFET structure minimizes the floating body effect, reduces self-heating, and improves on-current per unit area, providing consistent performance and tighter control over threshold voltage, thus addressing the limitations of conventional SOI MOSFETs.
Implementation Method 1
the inner and outer gates can operate with the same or opposite polarity to reduce the floating body effect and enhance channel control
Implementation Method 2
utilizing reactive ion-etching and selective etching to form a tubular silicon-on-silicon configuration
Implementation Method 3
self-alignment techniques are used to grow silicon epitaxially and form silicided gates and contacts
Data Source
AI summary
A nanotubular MOSFET device and a method of fabricating the same are used to extend device scaling roadmap while maintaining good short channel effects and providing competitive drive current. The nanotubular MOSFET device includes a concentric tubular inner and outer gate separated from each other by a tubular shaped epitaxially grown silicon layer, and a source and drain respectively separated by spacers surrounding the tubular inner and outer gates. The method of forming the nanotubular MOSFET device includes: forming on a substrate a cylindrical shaped Si layer; forming an outer gate surrounding the cylindrical Si layer and positioned between a bottom spacer and a top spacer; growing a silicon epitaxial layer on the top spacer adjacent to a portion of the cylindrical shaped Si layer; etching an inner portion of the cylindrical shaped Si forming a hollow cylinder; forming an inner spacer at the bottom of the inner cylinder; forming an inner gate by filling a portion of the hollow cylinder; forming a sidewall spacer adjacent to the inner gate; and etching a deep trench for accessing and contacting the outer gate and drain.