Digging deeper into a transmission electron microscope image of Intel's Optane by TechInsights.
TechInsights has released some of the results of its analytical work on Intel's Optane in the form of a TEM of Figure 1. It is from a detailed report TechInsights is preparing with the completed version soon to be available to the public.
Of particular interest (see the inset) is what appears to be the structure of the GST based memory element. Based on 20nm technology, it has an aspect ratio of about 2:1, indicating a thickness of about 40nm and width of 20nm.
The memory material appears to be capped at both ends by a barrier or interface layer, annotated in the inset diagram, with a thickness estimated at ~4nm. This interface layer while acting as a chemical reaction/alloying barrier it may also be serving as a heater electrode.
In the pictures released by TechInsights, it is assumed the active memory material is in its crystallized or conducting state. In fact, in the lower blocks of crystallized material, small crystallites appear to be present, although they are not as apparent in the upper blocks. This could be the larger crystallites have formed during the rigours of the processing steps for the upper part of the memory stack.
Received PCM wisdom (I use that oxymoron guardedly) teaches faster write (SET) times can be achieved if a large nucleating site of crystallized material is available from which the crystallization to create the (SET) state can start its growth. This avoids the need for a write time which includes sufficient time for both nucleation and crystal growth. Each Optane memory cell consists of a threshold switch as the memory isolation device and the memory itself. If, as it appears, the PCM element is vertically symmetrical, the role of the interface electrodes/barriers raises for me two interesting speculative possibilities representing new and different directions from what has gone before with respect to heater electrodes.
The first of these speculations is illustrated in Figure 2, where the two interface barriers (colored black) are of highly conducting material and primarily serve to prevent any chemical action between the PCM material and the rest of the electrode structure, with an equally important role of helping to create a symmetrical thermal structure.