Emerging Next Generation Memory Technologies
Over the past few decades, dynamic random-access memory (DRAM) and NAND flash memory have dominated the memory and storage industry as the primary technologies for volatile memory and non-volatile solid-state storage, respectively. However, both technologies are facing significant scaling challenges that are limiting future performance and cost improvements. This has resulted in a renewed focus on developing "next-generation" non-volatile memory technologies that can serve as possible replacements for existing memory and storage solutions. Some of the most promising emerging non-volatile memory technologies include resistive random-access memory (RRAM), spin-transfer torque magnetic random-access memory (STT-MRAM), and phase-change memory (PCM).
Resistive Random-Access Memory (RRAM)
RRAM is one of the most promising emerging Next Generation Memory Technologies
. It uses a metal-insulator-metal structure to allow electric currents to switch the resistance state of the insulator layer to represent data. RRAM offers simple fabrication process compatibility with back-end-of-line CMOS logic, high scalability with cell dimensions of tens of nanometers, fast switching speed of less than 10 nanoseconds, and high endurance of up to 1 trillion write cycles. RRAM is being developed as a potential non-volatile memory option that could provide byte-addressability like DRAM but with better performance and lower power consumption than NAND flash. Some industry players are targeting RRAM to replace SRAM and DRAM in memory hierarchies, while others envision it for storage-class memory applications.
Spin-Transfer Torque Magnetic RAM (STT-MRAM)
STT-MRAM uses magnetic tunnel junctions with two magnetic layers separated by an oxide barrier to represent data as parallel or anti-parallel magnetization states. The data state can be written by passing a spin-polarized current through the magnetic tunnel junction to toggle the magnetic orientation of the free layer. STT-MRAM retains data without power and offers almost unlimited programming endurance. It provides fast read/write times below 10 nanoseconds and data retention for years without refresh. STT-MRAM leverages manufacturing technology similar to DRAM and flash and can serve as a non-volatile and high-performance byte-addressable alternative to existing memory types. Major vendors are developing STT-MRAM for enterprise storage cache replacements, main memory, and embedded applications.
Phase-Change Memory (PCM)
PCM uses the amorphous and crystalline states of chalcogenic materials like germanium-antimony-tellurium (GST) to represent binary data. The chalcogenide materials can be switched between the states by applying heat produced from the flow of electric currents. The amorphous state represents a reset bit (1), while the crystalline state is a set bit (0). PCM provides high scalability down to cell sizes of 20-50 nanometers, fast switching times below 50 nanoseconds, and good endurance above 1012 cycles. It could potentially replace both flash memory and DRAM main memory. Significant industry efforts are ongoing to improve programming power consumption and design 3D cell structures for high-density PCM. The technology is already being incorporated in some commercial solid-state drives.
Future Prospects and Conclusion
Emerging next generation memory technologies like RRAM, STT-MRAM, and PCM promise performance advantages over NAND flash and compete with the density, cost, and capability limitations facing traditional memory types. They are being developed for applications spanning storage, main memory, embedded and specialized memory niches. Overcoming engineering challenges around cell scalability, manufacturing variability, and end-to-end device design will be crucial to make these memories commercially viable. Memory vendors and major chip makers are heavily investing in all the memory types to bring products to market in the next 3-5 years. With an expected ten-fold growth in global semiconductor memory and storage demand by 2030, next-generation memories are poised to transform computing architectures and enable new applications and form factors.