FW: PhD Orals - Nishant Patil, June 8, 2009, 3:30 pm, Packard 101
nppatil at stanford.edu
Fri Jun 5 09:02:41 PDT 2009
Carbon Nanotube Digital VLSI Circuits
Advisor: Subhasish Mitra
Department of Electrical Engineering
Time: 3:30 pm (refreshments served at 3:15 pm)
Date: Monday, June 8, 2009
Location: Packard 101
Carbon Nanotube Field Effect Transistors (CNFETs), consisting of
semiconducting single walled Carbon Nanotubes (CNTs), have several promising
applications such as extensions to silicon VLSI and large area electronics.
While there has been significant progress at a single-device level, a major
gap exists between such results and their transformation into VLSI CNFET
technologies. Major CNFET technology challenges include mis-positioned CNTs,
metallic CNTs, and wafer-scale integration. This work presents design and
processing techniques to overcome these challenges. Experimental results
demonstrate the effectiveness of the presented techniques.
Mis-positioned CNTs can result in incorrect logic functionality of CNFET
circuits. A new layout design technique produces CNFET circuits for
arbitrary logic functions that are immune to a large number of
mis-positioned CNTs. This technique is significantly more efficient compared
to traditional defect- and fault-tolerance techniques. Furthermore, it is
VLSI-compatible and does not require changes to existing VLSI design and
A CNT can be semiconducting or metallic depending upon the arrangement of
carbon atoms. Typical CNT synthesis techniques yield ~33% metallic CNTs.
Metallic CNTs create source-drain shorts in CNFETs resulting in excessive
leakage (Ion/Ioff < 5) and highly degraded noise margins. A new technique,
VLSI-compatible Metallic-CNT Removal (VMR), overcomes challenges posed by
metallic CNTs by combining layout design with CNFET processing. VMR produces
CNFET circuits with Ion/Ioff in the range of 10^3-10^5, and overcomes the
limitations of existing metallic-CNT removal approaches.
The above techniques are demonstrated for complex logic structures using
wafer-scale growth and transfer of aligned CNTs. Such an integrated approach
enables experimental demonstration of cascaded CNFET logic circuits.
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