Samsung Electronics and SK hynix are accelerating their research and development (R&D) of three-dimensional (3D) DRAM, and they are reported to plan to develop and initiate verification work on the initial prototype of '4F² DRAM' as early as this year, which changes the DRAM structure from horizontal to vertical. 4F² DRAM is a product that enhances performance, data transfer speed, and power efficiency by changing the structure of planar DRAM, which faces limits of miniaturization, to a vertical configuration. Samsung Electronics and SK hynix are reportedly planning to make changes to DRAM structure based on 4F² DRAM and then develop 3D DRAM.
DRAM stores data in cell units, which is the basic unit that can hold a piece of digital information, and the area occupied by one cell is expressed as F². Until now, a 6F² cell, with a bitline, which is a vertical line used to read and write data, occupying 3 units and a wordline, which is a horizontal line, occupying 2 units, was common. However, in order to reduce the size of DRAM and increase its integration density, there is a plan to develop 4F² DRAM by reducing these to 2 units each and arranging transistors, which serve as switches for DRAM, in a vertical structure.
According to industry sources on the 18th, Samsung Electronics and SK hynix have been accelerating the development of 4F² DRAM prototypes. A semiconductor industry official noted, "Before developing 3D DRAM, we plan to develop a level of 4F² DRAM prototypes that can operate products by the end of the year to verify performance and other factors," and said, "After verifying the commercial viability of the products in the market, we aim to transition to 3D DRAM based on the changed structure." Unlike Samsung Electronics and SK hynix, it is known that the U.S. company Micron will not develop 4F² DRAM and will proceed directly to developing 3D DRAM.
As Samsung Electronics and SK hynix faced the limits of miniaturization in planar DRAM, they pondered ways to overcome this. The performance and power efficiency improve as the line width of DRAM narrows, increasing its integration density. Currently, Samsung Electronics, SK hynix, and Micron are competing in the market for DRAM products of around 10 nanometers (nm), or one billionth of a meter. The product that has maximally reduced the line width to date is the 10 nm 6th generation (1c) DRAM, but from 10 nm and below, there is a prevailing view that changes to the DRAM structure are inevitable due to the rising manufacturing costs associated with the complexity of more advanced processes.
For these reasons, memory semiconductor corporations are opting to change the DRAM structure from planar to vertical to enhance performance and power efficiency. Samsung Electronics is reported to plan to introduce 4F² structured DRAM in the next generation after the 10 nm 7th generation (1d) DRAM product, while SK hynix plans to release it one generation later. If the roadmaps of memory semiconductor companies are realized, DRAM with a changed structure from planar to vertical could be mass-produced within three years. Overall performance of 4F² DRAM is expected to improve by nearly 50% compared to existing models.
As the DRAM structure undergoes significant changes, it is expected that there will also be changes in the processes, materials, and equipment introduced into manufacturing. Samsung Electronics, SK hynix, and others are collaborating with global semiconductor equipment companies like Applied Materials to develop processes. As the complexity of processes increases, they are reportedly exploring ways to ensure stable manufacturing and mass production, not just simple product development.
Lee Byung-hoon, a professor in the Department of Semiconductor Engineering at Pohang University of Science and Technology (POSTECH), said, "The costs of miniaturizing DRAM in planar structures are rising steeply, and there is a task to enhance performance. Currently, changing DRAM to a vertical structure is viewed as the only alternative," and he noted, "As significant changes to the DRAM structure are inevitable, the complexity of development and processes will be considerable."