Crossbar says that the technology can put a terabyte onto a single chip. The company has already measured filaments as thin as 6nm, and is confident that it can be shrunk further and that it will support multilevel cells.
Crossbar’s device is a silver filament ReRAM with a difference. For one, the silver filaments are in standard silicon dioxide, probably the most common product manufactured in a semiconductor fab. The other main difference is in the way that bits are addressed – the selection device.
A decided advantage of this technology is that the selection device is built into the cell. Other ReRAMS must use an external selection device, either a diode or transistor, and that can pose problems that The Memory Guy detailed in a prior post. This is an area that has received a lot of research funding but is still a thorny issue for many other technologies. The fact that ferroelectric memory or FeRAM has required a transistor has prevented the technology from shrinking enough to compete against modern NOR.
In Crossbar’s case, the connection between the top and bottom electrodes (shown in the diagram) is incomplete even when the cell is programmed. It takes a positive current to create that last layer of silicon atoms that connect the top electrode to the bottom one. When the read current is reversed then that connection does not form, removing the need for a selection device. A stronger current removes more silver atoms, preventing a weak forward current from creating a conductor.
The market for alternative technologies is limited – OEMs use the cheapest technology they can get away with, even though other technologies offer significantly better specifications. Silicon will retain its dominance over newer materials for as long as it can, and technologies like Crossbar’s will play a niche role until 3D NAND runs out of steam, which currently looks like it will happen 2-3 generations after 2D runs out of steam, which is 2-3 process generations away from where the market is today. For a deeper explanation of this see The Memory Guy’s earlier post on alternative memories.
When that does happen, then there will be a significant shift, and today Crossbar appears to have an important advantage.