New-Tech Europe Magazine | Q2 2022

Exploring liquid-based memories for ultrahigh-density storage applications

Maarten Rosmeulen, IMEC

A slowdown of the storage density scaling trend Today’s memory landscape comprises diverse types of memory, each of which plays its part in storing the data and feeding them back and forth to the computational part of the electronic system. In traditional computer hierarchies, fast and more expensive active memories (static random access memory (SRAM) and dynamic RAM (DRAM)) are distinguished from higher- latency and lower-cost storage solutions. Storing large amounts of data is primarily accomplished by NAND-Flash, hard disk drive (HDD), and tape technologies. While tape storage remains limited to long-term archiving, HDD and NAND- Flash are used for online and nearline storage applications: they both need to be accessed more frequently than tapes, with access times ranging from microseconds to seconds. NAND-Flash offers the lowest latency and power consumption of these two storage types. This non-volatile memory is present in all major electronic

end-use markets, such as smartphones, servers, PCs, tablets, and USB drives. Researchers have been able to significantly improve the bit density of the various storage solutions throughout the years to keep up with the growing demand for bits per volume. However, for some years now, HDD technology has not been able to follow the historical productivity trendline. A similar time lag is expected for NAND-Flash technology. 3D-NAND-Flash is projected to reach storage densities of up to 70Gbit/mm2 by 2029, which is a slowing down of circa four years with respect to the historical density scaling roadmap. Entering the post-NAND era After NAND-Flash scaling has saturated, we expect different storage technologies to co-exist, each trading off size, energy consumption, latency, and cost. New concepts for storage are being investigated, not to replace the existing storage solutions but to complement them in the latency/productivity space. Think

about DNA storage, targeting low-cost, ultrahigh-density but slow archival applications (such as preservation of (surveillance) video, medical and scientific data), or ferro-electric memory technology, projected to find its place in the lower-latency storage market segment. All these memories will be organized in different tiers and will jointly address the storage needs of the >100 zettabyte data era. In this article, we propose two new liquid-based storage concepts – colloidal and electrolithic memory – with the potential for ultrahigh-density nearline storage applications. These storage solutions could, for example, make archived ‘inactive’ data such as email archives, image & sound files, or other large documents accessible to users within seconds. From 2030 on, they might find their place between HDD and tapes, at significantly higher bit per volume but slower than 3D-NAND- Flash.

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