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A smart look inside Intel and Micron's 3D XPoint

Posted: 17 Aug 2015     Print Version  Bookmark and Share

Keywords:structural depletion effect  3D XPoint  NAND 

At Intel and Micron's recent 3D XPoint memory announcement, an interesting answer to a question popped up: "It does not use electrons. It's a material property."

I asked Intel to clarify this point, assuming the speaker meant to say it does not store electrons like a NAND memory, but it had nothing further to say. Could the responder have actually meant to say it stores data like NAND as a structural effect and relies on structural depletion effects?

Such an interpretation requires the speculative proposal of a possible memory mechanism. I call it the "egg yolk" model and named it the nanoparticle depletion RAM (NpdRAM). While there might be many possible implementations, Figure 1 illustrates two.

Reversible surface reaction

In operation, starting with the left hand side of Figure 1, we have conducting or non-conducting nanoparticles in a matrix of conducting material between two planar electrodes. The read current is able to pass between the nanoparticles, or even through and between them. For a preferred implementation, the current paths are shown in green.

To write the memory, a higher current or voltage pulse is used which by thermal, chemical reaction, electro-chemical or electro-migration effects cause a non-conducting surface layer to form on the nanoparticles. The formation of this layer depletes the inter-particle matrix material of one component, reducing its electrical conductivity. The two effects combined result in the high resistance memory state. This is shown in the upper left of figure 1, with the inter-particle detail on the far right. Red lines in figure 1 are used to indicate blocked current flow. In the rosy world of speculation, we do not have to specify the fine detail of the mechanism, only the concept.

The lower sequence in figure 1 shows a possible model where the high resistance surface coating is formed only on the leading edge of the nanoparticles. Once again, the combined effect of the barrier and inter-particle element depletion required to create the barrier results in a high resistance bulk material and the high resistance state of the memory. In this case, for example, the nanoparticles could be a something like a tantalum/titanium or tantalum/titanium oxide nanoparticle in a matrix of an oxide of manganese compound. The result would be nanoparticle rectifier junctions floating in a non-conducting matrix.

Depending on the particular mechanism, a pulse of higher amplitude might be used to reverse the process by thermal means or for the Ta/TaO or Ti/TiO in an oxide matrix nanoparticle example model a current pulse in the opposite direction would be used, with some degree of compliance. It is obvious without compliance that the process would result in barriers on the opposite leading edge and the same value of resistance.

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