In following up on the last Blog describing the patent issued to inventors at Micron in August, I came across two other patents issued to Micron in July related to ReRAM devices and fabrication. They are very different (no surprise there) but not just in content! The more recent (US patent 8,223,539: GCIB-treated resistive device, issued 17 July 2012), describes using a gas cluster ion beam (GCIB) to create the composition gradient (such as oxygen vacancies) that are believed to be critical to the operation of the resistive memory cells found in many ReRAM configurations. The idea is that instead of creating the composition gradient during cell fabrication (by multi-stage deposition, for example) or after the fact (by a forming process, for example), one can use GCIB to make the required modification in situ after the deposition and processing of a single resistive memory film. The advantages are obvious in terms of simpler film deposition and/or elimination of the forming process with its corresponding voltage requirements and electrical cycling/testing time. All of this is made clear in the Abstract and Background section making the figures and claims easy to follow, even more so bearing in mind that this is a patent rather than a publication in the open literature. I had one concern (which I’ll mention below) but I strongly recommend reading the Abstract and Background sections for a review of some of the key issues in ReRAM cell processing and fabrication. I tip my hat to the authors and the patent attorney who prepared the application. I could speculate that the examiner concurred with this view as the patent was approved (relatively speaking) rather rapidly having been filed at the beginning of 2010 and published mid 2011. This is express speed in my experience.
So is (and other patents) evidence that Micron are serious about resistive RAM and are actively developing a manufacturing process? I can obviously only speculate but it would appear that Micron are keeping track of the field and some of their most prolific inventors are devoting time and resources to the technology. Micron have also ‘published’ a TEM of a CBRAM cell (see the Keeping Track Blog), albeit in an investor briefing. So if I were a betting man (which I’m not), I would say that there is better than even chance that there are some wafers being processed in a Micron fab somewhere around the globe which could be described as resistive RAM (and maybe even oxide ReRAM) technology. And I’m not including wafers being processed as part of the Unity Semiconductor (now Rambus) agreement that Micron have publically announced.
That concern? A patent is only really defendable if infringements can be detected legally. That is why semiconductor processing patents so difficult to enforce. I’m no expert in GCIB but I imagine there are other processing techniques that could be used to achieve a similar effect (as indeed the inventors point out) .Further, I find it difficult to believe that GCIB would leave a unique signature that could be picked up by analysis of the end product.
United States Patent 8,223,539, Inventors: John Smythe. (Boise, ID). Gurtej S. Sandhu (Boise, ID). US Patent Office reference: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=8223539.PN.&OS=PN/8223539&RS=PN/8223539
Christie Marrian, www.ReRAM-Forum.com moderator