AI and high-performance computing (HPC) are evolving at an unprecedented pace, pushing traditional memory technologies such as DRAM and NAND flash to their limits. To meet the growing demands of the AI era, the industry is exploring emerging memory technologies which go beyond traditional memory.
Among these new memory technologies, storage-class memory1 (SCM) has emerged as a key development as it can bridge the performance gap between DRAM and NAND flash. Recognizing the potential of SCM, SK hynix has developed selector-only memory2 (SOM), a groundbreaking innovation that redefines SCM and strengthens the company’s AI memory portfolio.
1Storage-class memory: A class of emerging non-volatile memory technologies that combines the speed of DRAM with the persistent storage capabilities of NAND flash. It bridges the gap between DRAM and NAND flash in terms of performance, cost, and storage capacity.
2Selector-only memory (SOM): A cross-point memory device featuring a chalcogenide-based film which can perform both selector and memory functions.
This final episode of Rulebreakers’ Revolutions explores the journey behind SOM’s development, the key role of SK hynix’s rigorous R&D approach, and the implications for the future of AI and HPC.
![[Rulebreakers’ Revolutions] How SK hynix’s SOM Paves the Way for Next-Gen Memory in the AI Era](https://d36ae2cxtn9mcr.cloudfront.net/wp-content/uploads/2025/02/28011045/SK-hynix_Rulebreaker8_SOM_01.png "[Rulebreakers’ Revolutions] How SK hynix’s SOM Paves the Way for Next-Gen Memory in the AI Era")
The Mission: Going Beyond Traditional Memory With Next-Gen SCM
The AI era has sparked a data explosion. AI systems, from large language models3 (LLMs) to multimodal AI4, require high-performance memory to rapidly access and process this vast amount of data and perform complex computations. This next-generation performance must be balanced with affordability and energy-efficiency, placing further pressure on memory technologies.
3Large language model (LLM): Advanced AI systems trained on vast amounts of text data to understand and generate human-like text based on the context they are given.
4Multimodal AI: Machine learning models capable of processing and integrate different types of data, including text, audio, and video.
To meet these increasing demands, HPC systems are transitioning from traditional CPU-centric models to memory-centric architectures. By supporting data processing directly within memory, these memory-centric systems can minimize data movement to ultimately improve system performance and efficiency.
Amid this shift, the industry is exploring new memory technologies which can surpass the capabilities of traditional memory. Among them, SCM has emerged as a promising solution by bridging the performance gap between DRAM and NAND flash. As a non-volatile memory, SCM combines the speed and cost-efficiency of DRAM with the high capacity of NAND flash. Additionally, the advent of CXL®5 technology has enabled seamless connections between memory and devices such as CPUs, GPUs, and accelerators, creating new opportunities for SCM adoption in advanced computing.
5Compute Express Link®(CXL®): A next-generation interface that connects the CPU, GPU, memory, and other components to efficiently enhance the performance of high-performance computing systems.
Recognizing the capabilities of the technology, SK hynix took on the challenge of developing a next-generation SCM product—SOM—which could revolutionize the industry.
SK hynix’s SOM goes beyond traditional memory, breaking the barriers to next-generation memory
Beyond 3DXP: Rigorous R&D and Collaboration Unlock SOM
Before developing SOM, SK hynix had made great progress with an alternative SCM technology—3D XPoint (3DXP). Developed in the mid-2010s, 3DXP was a non-volatile storage technology that used phase-change memory (PCM)6 to store data through changes in material resistance states. It employed a transistor-less, cross-point architecture7 featuring selectors8 and memory cells placed at the intersection of perpendicular wires. By stacking 3DXP cells in a three-dimensional architecture without transistors, the product offered high memory density.
6Phase-change memory (PCM): A technology which enables non-volatile electrical data storage at the nanometer scale. PCM memory switching involves heating materials so they switch between amorphous and crystalline states, which correspond to the binary digits 0 and 1, respectively.
7Cross-point architecture: A memory architecture where data is stored at the intersection, or “cross-point”, of two or more lines in a grid-like structure.
8Selector: A device in a memory array that regulates the flow of current to and from a memory cell. This enables precise access to a specific cell while blocking unwanted paths for more accurate read and write operations.
Despite the potential of 3DXP, SK hynix identified challenges regarding the product’s scalability beyond 20 nm process technology. As a result, the company switched its attention to an alternative next-generation SCM product.
The company set about developing SOM, a groundbreaking cross-point memory device that uses a single chalcogenide9 -based film, known as dual-functional material (DFM), to perform both selector and memory functions. Compared to 3DXP, SOM eliminates the need for the separate selector and PCM setup. Instead, selectors in SOM are deployed without standalone memory cells to improve selector functionality. Moreover, SOM utilizes an optimized cross-point array with lower cell stack aspect ratios10 for better scalability and higher memory density.
9Chalcogenide: A chemical compound consisting of at least one chalcogen anion, such as sulfur, and an electropositive element, such as metal.
10Aspect ratio: Height-to-width ratio of memory cells.
One of the biggest changes from 3DXP was the inclusion of DFM in place of phase-change material. As a result of this switch, SOM offers advanced specifications. Firstly, the write speed is significantly improved as DFM, unlike PCM, does not require time to perform phase changes. While PCM required a high write current for joule heating during phase transitions, the use of DFM significantly reduced the necessary write current. In addition, DFM offers increased stability when operating at high temperatures, reducing thermal disturbance11. DFM’s improved heat resistance also ensures it offers enhanced cyclic endurance compared to PCM, boosting overall durability.
11Thermal Disturbance: A phenomenon where heat generated while programming one memory cell unintentionally affects the state of neighboring cells due to heat diffusion, potentially disrupting their data integrity.
SOM replaces the phase-change material used in 3DXP with DFM
The successful development of SOM would not have been possible without SK hynix’s rigorous approach to R&D and smooth internal collaboration. For example, the company discovered DFM during research on chalcogenide-based selector and memory materials. By applying a new bipolar operation instead of the conventional unipolar operation, the team found it could achieve both selector and memory characteristics simultaneously.
The company’s R&D approach also enabled a significant reduction in SOM’s power consumption compared to pre-development expectations. When conventional optimization approaches proved insufficient, this prompted a radical reexamination of materials, design, and operational algorithms. In response, various research teams came together to collaborate on the project and develop new approaches. They tested the application of new materials and operational techniques through simulations, addressing any potential issues. This meticulous process cut power consumption by approximately one-third from initial predictions, a crucial advancement in the development of SOM.
Unveiling the World’s Smallest SOM
SK hynix has successfully developed the world’s smallest SOM, the first fully integrated12 16nm half-pitch13 SOM. This revolutionary achievement in the SCM field was presented at the prestigious 2024 IEEE Symposium on VLSI Technology and Circuits (2024 VLSI Symposium).
12Fully integrated: Complete integration of circuits and manufacturing processes at the cell array level, unlike basic single-cell prototypes in academic research.
13Half-pitch: Half of the minimum center-to-center distance between interconnect lines in a semiconductor.
Compared to 3DXP, SOM offers a reduction in write speed from 500 nanoseconds (ns) to 30 ns and write current, which dropped from 100 microamps (µA) to 20 µA. In addition, cyclic endurance increased from 10 million to over 100 million cycles, highlighting SOM’s increased durability. SOM was also shown to have advanced persistency, the ability to retain data under extreme conditions, as tests proved it could retain data for over 10 years at 125°C.
SOM offers outstanding capabilities from rapid write speed to advanced persistency
Significantly, the 16nm SOM is the smallest, most scalable and high-performing cross-point memory solution on the market. As the AI landscape continues its evolution, the successful development of SOM strengthens SK hynix’s AI memory leadership, complementing products such as HBM, AiMX, and CXL Memory Module (CMM)-DDR5.
Looking forward, the research behind SOM will contribute to broader advancements in next-generation memory technology. Its impact extends to the growing field of heterogeneous integration, enabling innovative system integration approaches that cater to AI data centers and diverse AI solution providers. As computing architectures shift towards memory-centric computing, SOM’s technological breakthroughs will play a crucial role in shaping the future of AI and HPC.
Rulebreaker Interview: Myoungsub Kim, Global Revolutionary Technology Center (RTC)
To find out more about the company’s innovative approach to SOM development, the SK hynix Newsroom spoke with Myoungsub Kim of the Global Revolutionary Technology Center (RTC), which conducts R&D of next-generation semiconductors. Kim discusses the major challenges faced when developing SOM as well as the rulebreaking mindset adopted by employees.
What were the major challenges that you faced during the SOM development process?
“The main challenge was making the decision to become a first mover and begin R&D of the world’s first half-pitch 16nm SOM. This process involved transitioning from focusing on conventional PCRAM-based 3DXP memory while also preparing for the scalability and performance advantages of SOM, despite the uncertainties involved.”
What is your proudest moment when leading SOM R&D?
“At the 2022 IEEE International Electron Devices Meeting (IEDM) conference, we were the first in the industry to claim the potential performance and scalability advantages of SOM. This led to my proudest moment when we were able to prove these claims at the 2024 VLSI Symposium. We presented our research on the world’s first fully process-integrated half-pitch 16nm SOM, achieving the industry’s smallest size.”
What aspects of SK hynix’s corporate culture help foster creativity and overcome limitations?
“Above all, SK hynix’s new Code of Conduct is founded on SKMS’s VWBE14 and SUPEX15 principles. In particular, the pursuit of ‘bar raising,’ which encourages employees to continually obtain higher standards in the pursuit of excellence, and the ‘one team’ approach, which fosters collaboration as a unified team, have enabled us to continuously showcase our creativity and overcome limitations.
14Voluntarily, Willingly, Brain, Engagement (VWBE): One of the employee values emphasized by SK Management System (SKMS).
15SUPEX: An SK hynix philosophy carrying the meaning “super excellent,” SUPEX represents the company’s mission to achieve the highest possible levels of achievement.
“To sum up, I believe there is a recipe for innovation: embrace new changes with a spirit of challenge, experiment in the face of uncertainty without fear of failure, and learn with flexibility.”
<Other articles from this series>
[Rulebreakers’ Revolutions] How MR-MUF’s Heat Control Breakthrough Elevated HBM to New Heights
[Rulebreakers’ Revolutions] Innovative Design Scheme Helps HBM3E Reach New Heights
[Rulebreakers’ Revolutions] How SK hynix’s Design Innovations Pushed GDDR7 to New Limits of Speed
[Rulebreakers’ Revolutions] How CXL Tech Expands Data Center Memory Scaling Boundaries in the AI Era
