Abstract
Despite hitting major roadblocks in 2-D scaling, NAND flash continues to scale in the vertical direction and dominate the commercial nonvolatile memory market. However, several emerging nonvolatile technologies are under development by major commercial foundries or are already in small volume production, motivated by storage-class memory and embedded application drivers. These include spin-transfer torque magnetic random access memory (STT-MRAM), resistive random access memory (ReRAM), phase change random access memory (PCRAM), and conductive bridge random access memory (CBRAM). Emerging memories have improved resilience to radiation effects compared to flash, which is based on storing charge, and hence may offer an expanded selection from which radiation-tolerant system designers can choose from in the future. This review discusses the material and device physics, fabrication, operational principles, and commercial status of scaled 2-D flash, 3-D flash, and emerging memory technologies. Radiation effects relevant to each of these memories are described, including the physics of and errors caused by total ionizing dose, displacement damage, and single-event effects, with an eye toward the future role of emerging technologies in radiation environments.
Highlights
M EMORY is a key ingredient in computing
From the perspective of radiation effects, technologies can broadly be split into two categories based on their storage mechanisms: charge-based storage and resistance-based storage devices
floating gate (FG) memories tend to be sensitive to relatively low radiation doses due to the direct interaction of ionizing radiation with their stored charge
Summary
M EMORY is a key ingredient in computing. The other key ingredient, logic, relies on one device—the transistor, and one circuit primitive, complementary metal– oxide–semiconductor (CMOS), to carry out all computations. The majority of modern caches store each bit in a static random access memory (SRAM) cell, which typically consists of six transistors These transistors can be optimized for speed or density depending on the application and utilize the same CMOS process technology as the logic core. It would be inefficient to store all of a system’s data on the main memory, due to the relatively high cost of DRAM These considerations define the requirements for the third level on the hierarchy: storage. Nonvolatile memory (NVM) is of low cost and high density, allowing typical personal computing systems to utilize GBs to terabytes (TB) of persistent storage This data can still be accessed with latencies on the order of 10–1000 μs for a modern solid state drive (SSD), depending on the specific details. These have the advantage that they can be integrated into the back end-of-line (BEOL) of an existing CMOS logic process, suggesting that embedded memory may be an important application for these emerging technologies [3]
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