For decades, the capacity of primary memory in memory modules has doubled in a predictable binary scale, from, for example, 4 to 8, 16, 32, 64 GB and so on. That this happened is a combination of the manufacturers with new generations aiming to double the capacity and being able to do this by shrinking the distance between transistors in memory circuits of the Dynamic Random Access Memory (DRAM) type.
The complexity of DRAM and the fact that capacitors must have a certain size to hold a charge mean that the technology has basically reached the end of the road in terms of shrinkage. The next generation of DRAM from Samsung and SK Hynix will be manufactured at 12 nanometers, and it won’t be much smaller than that. The duo and its American competitor are therefore working on the next paradigm shift spelled 3D DRAM. The concept behind 3D DRAM is not to rely on shrinking transistors and capacitors, but to take existing sizes and “build on top” with layers of memory cells on the same circuit.
This is already done with another different type of memory – NAND – used in everything from SSDs to phones and USB sticks. The technology known as 3D NAND was commercialized by Samsung back in 2013 and came about in response to the shrinking of NAND for similar reasons as DRAM stopping at 16 nanometers. Today, Samsung is joined by SK Hynix, Micron and YMTC, all providing 3D NAND with around 170-230 memory cells stacked on top of each other and capacities of up to 1 terabit (128 gigabytes) per circuit.
Micron’s latest generation of 3D NAND has 232 layers of memory cells
Until 3D DRAM is a reality, development on the capacity front is expected to stagnate, especially at the consumer level. To meet the difficulties, non-binary sizes are included in the DDR5 specification, allowing for “in-between sizes” such as 24, 48 and 96 GB. Memory modules in capacities of 24 and 48 GB have just started to find their way onto the market.
On the server side, continued advancement is to be expected, but this through costly solutions that are only economically justifiable for customers with strong purchasing power in data centers. One way to increase capacity without further shrinkage is through Through-Silicon Via (TSV) technology, where vertical wiring paths in memory circuits allow these to be stacked on top of each other to increase capacity per memory module. In that way, Samsung will deliver DDR5 modules of 512 GB and 1 TB each.
By next year or so, details about the electrical characteristics of 3D DRAM will be revealed, determining the direction of their development. – Cha Seon-yong, chef på SK Hynix Future Technology Research
The commercialization of 3D DRAM is still a long way off and only in 2024 is SK Hynix expected to reveal the first details of its variant. Where in time Samsung and Micron stand with their respective technologies is not known, but it is likely that they both also have several years to go before they have 3D DRAM that is ready for store shelves.
Source: Business Korea
