LONDON – Researchers at the University of Pennsylvania (Philadephia, Pennsylvania) led by Professor I-Wei Chen have developed a resistive-switching memory device based on silicon dioxide.
The key to the memory is the inclusion of atomically dispersed platinum on a random basis, the variation of the distances between the platinum atoms and their relationship to a quantum mechanical property known as the electron localization length.
Silicon dioxide is generally considered an insulator but in films of nanometer-scale thickness and random dispersion of platinum atoms it can be made to display a memory effect. The development of a resistive-switching non-volatile memory based on the CMOS-compatible material offers the prospect of an ReRAM memory with useful properties but a simpler material structure to some alternative proposals based on metal-oxide films.
The University of Pennsylvania research has been reported in a number of learned papers on different aspects of the technology and on models of the behavior during 2011. The behavior is ascribed to the tunneling of electrons between atomically dispersed platinum in amorphous silicon dioxide thin films between platinum and molybdenum electrodes. It is said that the trapped electrons and the local Coulomb barriers which can also be created can "choke off" the electron passage in the nearby nanometallic paths, making non-volatile memory possible. Nanoparticles of platinum, which may not even be metallic according to their optical responses, are sometimes present at higher platinum concentrations but are not required for the operation of the device.
Professor Chen is due to present an update on the technology and comparison with other ReRAM systems at a one-day symposium on emerging non-volatile memory technologies due to be held Friday April 6 in Santa Clara, California.
The electron transport system through the material is generally applicable to random metal-insulator mixes and has been demonstrated in silicon oxide and silicon nitride glasses with platinum inclusions as well as in perovskite transition metal oxides.
Professor Chen told
EE Times that the materials are quite easy to make by the use of co-sputtering on to a substrate, although the exact composition together with final film thicknesses are significant in tuning the memory effect and voltage scheme. The research group has made individual devices with sizes down to 20-micron by 20-micron with film thicknesses of between 5-nanometer and 30-nm to 40-nm. "I see no evidence why it should not scale," Professor Chen said.
Next: Bipolar resistance switching