1. Integrating Carbon Nanotube with Phase Change Memory
Mentee – Yuan Dai
Mentor – Feng Xiong

2. Timeline of Data Storage
MP3 player, photograph,
, text message, documents, program code …
high-density
low-power
high speed
robust data storage
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3. Motivation
Phase Change Memory - “Universal Memory” - Non-volatile - Fast access time - Large dynamic range - High endurance - High packing density - Radiation resistant
Parameter
DRAM
SRAM
NAND Flash
PCM
Non-volatile No
Yes
Access time
10 ns
2 ns
25 µs
50 ns
Endurance
>1015
105
1012
Density 1X 4X
2~4X
Voltage
1.5 V
10 V
R. Agarwal et al., Nat. Nano. , 2007
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4. Phase Change Material Crystalline
Chalcogenide compound: Ge2Sb2Te5 (GST)
3 crystal states: amorphous,
face center cubic ,
Hexagonal close packed
Fast crystallization time
Large contrast in optical and electrical properties
Promising candidate for random access memory (RAM)
Amorphous
A. Kolobov et al., Nat. Mater. (2004).

5. Electrical & AFM Characterizations
IDVG sweep:
metallic or semi-conducting
IDVD sweep :
number of connections
Keithley 4200
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6. CNT Interconnects for Lateral PCM DeviceCu
TiN
GST
SiO2
(Heater)
High bias  CNT breakdown
Oxidation (in air)  Nano-scale gap (30 ~ 300 nm)
GST deposition  Lateral GST cell with CNT electrodes
Chen & Pop, IEEE Trans. Elec. Dev. (2009).
CNT Breakdown in Air
CNT gap

7. Antifuse Device Schematics
OFF state
ON state
41 nm Ti/Pd
70 nm SiO2
p+ Si
CNT
Crystalline GST
Amorphous GST
10nm GST
Typical CNT device
Electrical cutting of CNT – nano-scale gap
10 nm GST deposition (DC sputtering)
Sputtered GST – amorphous phase and NOT conductive

8. Electrical & AFM Characterizations
Threshold switching at a
snapback voltage Vsb
Amorphous -> crystalline phase
change due to Joule heating
Switching current ~ 1 μA
Switching voltage 3 ~ 10 V
GST “bubble” formed in the
CNT gap
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9. 3D FE model of the nanotube-PCM device
COMSOL Multiphysics
Comsol Multiphysics
3D FE model of the nanotube-PCM device
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10. COMSOL Multiphysics
COMSOL Simulation Flowchart
COMSOL is a commercial software package for finite element analysis
Especially useful for coupled phenomena, or multiphysics applications
More powerful 3D version of MATLAB PDE Toolbox
Determine Problem Type
Set Geometry
Set Physical Properties/ Boundary Conditions
Meshing
Solve the Problem
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11. My Mentor, Feng Xiong The P.U.R.E Committee All of You
Acknowledgments
My Mentor, Feng Xiong The P.U.R.E Committee All of You

12. Thank You