Carbon Nanotube-Based Nonvolatile Random Access Memory for Molecular Computing Thomas Rueckes, et al. Science 289, 94 (2000)

Overview Non-volatile memory can retain the stored information even when not powered. Different types of memory: MROM, EPROM, EEPROM, OTP, NAND/NOR Flash, Phase- change, MRAM, etc NAND Flash is by far the largest percent of all NVM in the market today (Toshiba/SanDisk, Samsung, Hynix)

Structure and Principle of Operation Single-Walled Nanotube (SWNT) crossbar array Bi-stable electromechanical switch OFF and ON states corresponding to elastic energy at finite separation and van der Waal energy minima Switching between the states is accomplished by transiently charging SWNT to produce attractive and repulsive forces Si substrate SiO 2 Metal contact (Paladium?) “Organic or Inorganic support structure” van der Waal contact

I-V Characteristics Upper 3,4 Lower 1,2 ON OFF R ON /R OFF ~ 10 5 R ON /R OFF ~ 10

Program/Erase/Read ON/OFF state can be detected by measuring the resistance of the junction -V +V V2 V1 +V Program V=4.5V Erase V=20V Read

Issues (according to the authors) Random distribution of metallic and semiconducting SWNT Crosspoint structure has multiple pathways and would need directional element like diode Growth

Key Challenges to Practical Applications Retention—ability to retain stored states for long periods under adverse conditions Endurance—ability to switch multiple times without degrading performance Scalability—program/erase voltages Array Efficiency—user-bits vs. support circuitry

Questions? Thank You!