Dr. Neale, thanks for the info. Many attempts to bring PCM retention to a higher level by using a material other than GST have fallen short. We also have to remember the high resistance state decreases resistance with temperature.
Regarding the Hynix patent app. The first AgLnSbTe is likely a typo. Paragrapgh 0036 under Detailed description reads AgInSbTe. You had me looking to see if there was an indication of which Lanthanide they were using. There is some research that suggests doping the chalcogenide with various of the Lanthanides will mitigate the problems with thermal stress and migration.
Resiston –Ahead of the IEDM 2011 paper your reservations re PCM elevated temperature data retention might find an answer in a recent patent application from Hynix (US2011/0193046A1). As well as the usual broad-brush material composition claims, one material composition is cited as of particular interest, AgLnSbTe.
That same patent also discloses a matrix isolation fabrication technique using an SOI structure, allowing two diodes in parallel to share the reset current and so alleviates the current density problem in the silicon. The need for this suggests the current density in the PCM cell remains high.
For me this raises the question as to the immunity of any new material from element separation associated with high current density and electrochemical effects. To be credible the claimed elevated temperature (200C for 10 Years) will need to be supported by solid evidence as a function of write/erase lifetime and in a fully processed device matrix.
The language of the abstracts “describe a complete technology platform” and data published to date suggests that this 1G-bit device may be relegated to demonstration status rather than announced as a commercial product; as the three 1G-bit PCMs (Numonyx/Micron/Samsung) that have gone before. IEDM 2011 and post-IEDM will be an interesting time for PCM followers.
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