Memory effects of carbon nanotubes as charge storage nodes for floating gate memory applications

Abstract

A nonvolatile flash memory device has been fabricated using carbon nanotubes ͑CNTs͒ as a floating gate embedded in HfAlO ͑the atomic ratio of Hf/ Al is 1:2͒ high-k tunneling/control oxides and its memory effect has been observed. Capacitance-voltage ͑C-V͒ measurements illustrated a 400 mV memory window during the double C-V sweep from 3 to −3 V performed at room temperature and 1 MHz. Further studies on their programming characteristics revealed that electron is difficult to be written into the CNTs and the memory effect of the structures is mainly due to the holes traps. The memory window width can remain nearly unchanged even after 10 4 s stressing, indicating excellent long term charge retention characteristics. We therefore suggest that the CNTs embedded in HfAlO can be potentially applied to floating gate flash memory devices. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2179374͔Since their discovery in the early 1990s, 1 carbon nanotubes ͑CNTs͒ have attracted much attention, both of scientific and technological interest, for possible nanoelectronic applications. To date, a number of nanoelectronic devices have been realized with CNTs, such as field effect transistors, 2-4 room-temperature single-electron transistors, 5 logic gate circuits, 6 inverters, 7 and electromechanical switches. 8 Very recently, the prototypes of memory devices based on CNT field effect transistors were also reported, 9-12 demonstrating another significant extension of CNTs applications. From then on, several groups have carried out research on the CNT-based memories. [13][14][15][16][17] In these research works, the CNTs were synthesized on a conductive Si substrate capped by several hundred nanometers of SiO 2 . Metal electrodes were evaporated on the CNTs to form source and drain electrical contact to them. The conductive Si substrate actually acts as the gate of the memory device. The function of the CNTs was the current channel, and the memory effect of the devices was attributed to the charges injected from the CNTs to the defects or charge traps in the dielectrics or the interface between the CNTs and the oxides. 15-17 The CNTs were not used as the charge storage nodes.For commonly studied flash memory devices, Si, 18 Ge, 19 and Si 1−x Ge x ͑Ref. 20͒ nanocrystals are widely used as the charge storage nodes and the memory structures are sandwiched with nanocrystals embedded in the SiO 2 or high-k dielectrics. But up to now, there is no report on flash memory devices using CNTs as a floating gate. In terms of electrical properties, CNTs have many unique advantages for the application in memory devices such as tunable band gap, high thermal stability and chemical inertness, perfect sidewall structure, and nearly zero surface states. 21,22 These unique properties are very favorable for their application as the charge storage nodes in the memory devices. In this letter, we report the fabrication of the HfAlO/ CNTs/ HfAlO/ Si memory structures and characterization of the unique memory characteristics of CNTs using as the c...

Wide memory window in graphene oxide charge storage nodes

“…10 In a separate experiment where the GO sheets are first thermally reduced to G, it is observed that the memory window in the C-V hysteresis is reduced to 1.5 V, as shown in Fig. 3.…”

“…This window is still about four times larger than CNTs-based charge storage nodes. 10 The XPS spectrum shows that the proportions of oxygenated carbon have reduced significantly after annealing.…”

“…10 Catalytic impurities and bundling of CNT make the processing of the CNT-embedded layers challenging. Recently, nonvolatile memory based on G sheets has been reported; 11 the operation was based on the formation and breaking of carbon atomic chains that bridged the G junctions.…”

Pentacene-based metal-insulator-semiconductor memory structures utilizing single walled carbon nanotubes as a nanofloating gate

“…6 CNTs embedded in a high-k dielectric were reported as a nanofloating gate in MIS (Ref. 7) and transistor memory devices. 6 The nearly ideal surface states enhances CNTs' charge retention characteristics compared to that of metallic NCs.…”

Highly‐Ordered Covalent Anchoring of Carbon Nanotubes on Electrode Surfaces by Diazonium Salt Reactions

“…Since their discovery in 1991, carbon nanotubes (CNTs) have attracted growing interest in view of their unique mechanical and physicochemical properties, [1,2] and have successfully been applied in microelectronics [3][4][5][6] such as memory devices, [4] switches, [5] supercapacitors, [6] and in the biomedical area as drug-delivery devices [7] and biosensors. [8][9][10][11] The oriented assembly of CNTs on an electrode surface offers further possibilities with respect to both electrochemical biosensors because of the high electron-transfer rate along the tube, and the attachment of redoxactive molecules (or redox enzymes) to the ends of the CNTs.…”