The design of re-writeable ultra-high density scanning-probe phase-change memories

A systematic design of practicable media suitable for re-writeable, ultra-high density (> 1Tbit/sq.in.), high data rate (> 1Mbit/s/tip) scanning probe phase-change memories is presented. The basic design requirements were met by a Si/TiN/GST/DLC structure, with properly tailored electrical and thermal conductivities. Various alternatives for providing re-writeability were investigated. In the first case amorphous marks were written into a crystalline starting phase and subsequently erased by re-crystallization, as in other already-established phase-change memory technologies. Results imply that this approach is also appropriate for probe-based memories. However, experimentally the successful writing of amorphous bits using scanning electrical probes has not been widely reported. In light of this a second approach has been studied, that of writing crystalline bits in an amorphous starting matrix, with subsequent erasure by re-amorphization. With conventional phase-change materials, such as continuous films of Ge_{2}Sb_{2}Te_{5}, this approach invariably leads to the formation of a crystalline “halo” surrounding the erased (re-amorphized) region, with severe adverse consequences on the achievable density. Suppression of the “halo” was achieved using patterned media or slow-growth phase-change media, with the latter seemingly more viable.