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

Timeline of Data Storage MP3 player, photograph, e-mail, text message, documents, program code … high-density low-power high speed robust data storage DAI

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 DAI

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).

Electrical & AFM Characterizations IDVG sweep: metallic or semi-conducting IDVD sweep : number of connections Keithley 4200 DAI

CNT Interconnects for Lateral PCM Device Cu 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

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

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 DAI

3D FE model of the nanotube-PCM device COMSOL Multiphysics Comsol Multiphysics 3D FE model of the nanotube-PCM device DAI

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 DAI

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

Thank You