CARBON NANOTUBE BASED NONVOLATILE MEMORY DEVICES
Abstract
The technology progress and increasing high density demand have driven the nonvolatile memory devices into nanometer scale region. There is an urgent need of new materials to address the high programming voltage and current leakage problems in the current flash memory devices. As one of the most important nanomaterials with excellent mechanical and electronic properties, carbon nanotube has been explored for various nonvolatile memory applications. While earlier proposals of "bucky shuttle" memories and nanoelectromechanical memories remain as concepts due to fabrication difficulty, recent studies have experimentally demonstrated various prototypes of nonvolatile memory cells based on nanotube field-effect-transistor and discrete charge storage bits, which include nano-floating gate memory cells using metal nanocrystals, oxide-nitride-oxide memory stack, and more simpler trap-in-oxide memory devices. Despite of the very limited research results, distinct advantages of high charging efficiency at low operation voltage has been demonstrated. Single-electron charging effect has been observed in the nanotube memory device with quantum dot floating gates. The good memory performance even with primitive memory cells is attributed to the excellent electrostatic coupling of the unique one-dimensional nanotube channel with the floating gate and the control gate, which gives extraordinary charge sensibility and high current injection efficiency. Further improvement is expected on the retention time at room temperature and programming speed if the most advanced fabrication technology were used to make the nanotube based memory cells.
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