CeRAM paper broadens material scope, highlights role of carbon
Researchers drawn from Cerfe Labs, Symetrix and several universities have published a detailed paper on correlated electron random access memory (CeRAM) that provides additional insights into this emerging non-volatile memory.
CeRAM has been proposed as a bulk-switching non-volatile memory with the potential to outperform resistive RAMs, which are usually based on the making and breaking of filamentary conduction paths between electrodes (see ARM spin-off to develop CeRAM memory). However, some ReRAM technologies have been subject to more R&D and are either already in the market (see MCUs with embedded PCM meet automotive needs) or closer to market (see Weebit moves ReRAM on to ‘secret-sauce’ materials).
The CeRAM paper, published in the American Institute of Physics journal APL Materials, provides detailed conductive characteristics and theoretical analysis of carbon-doped transition-metal oxides. It records the observation of the non-volatile memory effect in additional materials to the nickel-oxide of earlier work by Symetrix. The intended level of carbon-doping is about 1 percent.
CeRAM is notably different from other emerging NVMs in that it is not based on the physical re-organization of the crystal lattice. Such physical reorganization brings with it requirements for ‘forming’ and potential wear-out mechanisms. Instead CeRAM relies on carbon-doping to create additional energy band gaps so that a naturally insulating metal-oxide can be switched between conducting and insulating states. This so-called correlated electron or electron orbital Mott transition is reversible, inherently fast and takes place throughout the bulk of a material.
However, proving that this is exactly what is going on in specific materials and device structures – and that other mechanisms are either not present or can be discounted – is difficult. This paper goes some way to achieving that.
Familiar transition metal-oxides
Results are given for NiO, PbNiO3, HfO2, YTiO3, and Bi2O3 showing the universal nature of correlated electron switching. These are measured on 1T1R memory cells down to 47nm diameter. Although intriguingly both ReRAMs and CeRAM are moving towards similar transition-metal material systems. Some of these are already in use in CMOS IC production as insulators.
The paper reports write times of 2ns, high temperature retention (24 hours at 473 K), and 90 percent functional yield in 1kbit arrays. The fact that device switching allows the setting of variable resistance levels, which offers the possibility of multi-level cell memories and scope for analog neuromorphic in-memory computing.
Cerfe Labs Inc. (Austin, Texas) was founded in 2020 by senior research executives from processor licensor ARM to develop bulk-switching, non-volatile memories capable of scaling to advanced nodes. The name is a portmanteau of Cerfe’s primary areas of interest; CeRAM and ferroelectric memories.
Cerfe is working on CeRAM under a license from the original developers of the technology at Symetrix Corp. (Colorado Springs, Colo.).
The paper has appeared in the American Institute of Physics journal APL Materials under the title Universal non-polar switching in carbon-doped transition metal oxides (TMOs) and post TMOs
Related links and articles:
ARM spin-off to develop CeRAM memory
MCUs with embedded PCM meet automotive needs
Weebit moves ReRAM on to ‘secret-sauce’ materials