I don't quite understand why they use Ag in a circuit. Silver is known for its serous migration effects under an electrical field. The heat by current makes this even worse. I don't know how they solve the reliablity issue using such a material.
Resistion-I went back and had a look at K-H Kim's thesis. It states "..movement of Ag ions in the a-Si matrix..." Suggesting a belief that those were ions moving towards the cathode, with a positive charge. Belief because there was not much evidence provided to prove the point; perhaps I missed it. It is not clear to me what elements provide for the oxidation-reduction prcess to form a ECM cell and provide the positive charged ions that you suggested need to be neutralized. Describe that for me with the elements available and you can have your positively charged Ag ion.
The thesis also states ".. Current can only flow through the device with a positve bias.." By that I think it is the current for programming to the low resistance state making the Ag electrode positive. The reason for that is because of the non-linear element that is somewhere in structure. Current does flow in the reverse direction for erase.
Resistion-Not so much a complication, for me more a process of elimination of all possibilities. I tried to look at all the possible ways in which an electrochemical cell might be formed from the elements available in the Crossbar memory structure.
Resistion- Hydrogen should be the only other element that is available in a-Si and would have the possiblity of being mobile. (Remember a-Si is a sub hydride of silicon). I am not sure if it possible to make a silver-hydrogen ECM cell where oxidation-reduction takes place in the OIL RIG* sense. I did look at the possibilty that the movement of Ag into the a-Si lattice would displace hydrogen into the void at the depleted surface of the Ag electrode. I would think that would most likely trigger the crystalization of the a-Si and that would not be reversible.
For an Ag-aSi-xtalSi Crossbar memory structure I also looked at the possibility that solid state epitaxy on the single crystal surface might account for the diode/non-linear element (or even be a way of creating one). In the the distant past I did use palladium as a catalyst for low temperature solid state epitaxy of a-Si on xtal crystal after switching for use as a PROM. Some of the details are in my US patent No 4,174,521.
Sorry *OIL-RIG Oxidation Is Loss-Reduction Is Gain, of electrons
Resition-If you mean there is some form of interface layer at the Pt electrode that is responsible for the switching and the mecahnism is oxidation-reduction, then I think it is necessary to show the chemical/electro-chemical reaction involved.
ECM or not, for the moment because Ag does not need much encouragement to move in silicon, amorphous or xtal, then for me heat and electromigration/electric field effects suffice. My worry with the Crossbar device is to create the filament, material must be moved from the silver electrode leaving what must be an Ag depleted spongy like contact region of nano filaments. Does that material return to the same place when the polarity is reversed, my view is that the material forms mutiple short filaments around the region from where the silver was originally removed. That is along the lowest resistance paths.
The nice thing about having an interface layer close to the passive electrode that switches and is responsible for the memory effect is the suspect contact at the Ag electrode depleted region once formed does not get modified. However, I think memory devices that require a forming step different from normal operation do not have much of a future. from my experience with antifuses that used amorphous silicon threshold switching occurred on programming, for the Crossbar device will the first switching event in the virgin a-Si be the same a subsequent ones.
I do have a number of slides that we prepared for a possible article that illustrate what I see as the problem for Crossbar, if you contact me I will send them to you. Also if you want what I think might be an example oxidation and reduction at a single site then perhaps CeRAM might be a better example-more on that later.
Ron, just came across this today, thought back to this discussion. Although it seems the filament growing forward into Si seems different from the deposition "backward" toward silver, it looks like he (founder of Crossbar) is still classifying the Crossbar memory along with the other CBRAMs (as ECM). It is possible the electrochemical reduction is occuring in the silicon instead of a Pt electrode.
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