IBM Reveals Radiation Hard Non-volatile Switching and Memory Devices Using Vertical Carbon Nanotubes

International Business Machines Corporation (IBM) (Armonk, NY) has developed non-volatile and radiation-hard switching and memory devices using vertical nano-tubes that are reversibly held in state by van der Waals' forces and methods of fabricating the devices. Means for sensing the state of the devices include measuring capacitance, and tunneling and field emission currents, according to IBM inventors Toshiharu Furukawa, Mark Charles Hakey, Steven John Holmes, David Vaclav Horak and Charles William Koburger, III in U.S. Patent 7,668,004. The devices are formed by a photolithography process.

There is a continuing need to improve the performance, decrease the power consumption and decrease the dimensions of solid-state electronic devices, particularly those used as cells for memory devices and as switching devices. Further, as semiconductor device sizes decrease, various sources of radiation have been shown to cause changes in state of semiconductor-based memory and switching devices. Therefore, there is a need for memory and switching devices that are both non-volatile and radiation hard. 

IBM uses electrically conductive single-wall and multiple-wall carbon nanotubes comprised of sp²-hybridized carbon.  Electrically conductive or semi-conductive single-wall and multiple wall nanotubes comprised of other electrically conductive or semi-conductive materials may be substituted for electrically conductive or semi-conductive single or multi-wall carbon nanotubes.

IBM CNTs  are grown on electrically conductive bitlines formed on or embedded in an insulating layer by exposing bitlines to a vapor mixture of a CNT precursor and optionally a CNT catalyst at an elevated temperature. In one example, the CNT precursor is hydrocarbon or hydrocarbon isomer mixture and the bitline comprises iron (Fe), cobalt (Co), nickel (Ni) or other materials known in the art. In one example, formation of CNTs is performed at elevated temperatures between about 400 degree C. to about 900 degree. C.

When non-carbon SWNTs and MWNTs are substituted for CNTs, besides changes to reactants used to form the non-carbon SWNTs and MWNTs, appropriate changes to the composition of the bitline may be required, however, the material of the bitline remains an electrically conductive material.