Why is Micron stock down? CXMT's 4F's square DRAM breakthrough explained

Micron Technology shares fell Monday, October 12, as Chinese memory maker ChangXin Memory Technologies (CXMT) released a next-gen DRAM design that can reshape the global memory-chip landscape.

Micron (MU) stock dropped 3.58% to $992.21 in early trading, down roughly 15% from its June all-time high. South Korean rivals also tumbled, with SK Hynix down 4.52%, Samsung Electronics losing 4.39%, and KOSPI falling to 3.5%.

The selloff followed CXMT’s announcement over the weekend that it had achieved “key progress” on a new memory-cell architecture focusing on increasing storage density (an area the world’s largest memory makers are all racing to dominate).

What is the 4F square design?

The "4F square" structure is at the heart of the innovation, in which each memory cell takes up an area of four squares of F, where F is the smallest line width of a semiconductor device. This makes possible the packing of more memory cells into a single chip, resulting in higher storage density.

Currently, mainstream DRAM chips use the 6F square cell structure. Switching to the 4F square structure amounts to a paradigm shift from horizontal to vertical transistor channels.

According to CXMT, the secret of its architecture lies in the Vertical Surrounding Gate transistor, which employs a vertical gate structure to solve the problem of leakage while drastically decreasing the unit area.

Significance of DRAM chips

According to CXMT president Cao Kanyu, the company aims to unveil a new memory solution for servers based on the new architecture by the end of 2026, including the next-generation DDR5 RDIMM by the end of 2026. The new architecture can raise the memory density by 30%–50%.

The major manufacturers of the world’s leading DRAMs are all working towards the technology. SK Hynix came up with the roadmap for 4F square in 2025. It was also stated that Samsung would start mass-producing sub-10 nanometre DRAM on this roadmap by 2028.

What next for Micron?

There is another possible issue for Micron from Taiwan, where the union wants a permanent share of profits, in which 15% of operational profit should be given to the employees as a quarterly bonus. Taiwan accounts for more than 80% of Micron's workforce.

The overall semiconductor industry has been suffering. The positioning in the options market for chip ETFs has been heavily put-biased.