MAY 20258 APACAPACIN MY OPINIONCode storage plays a crucial role in modern electronics, enabling the execution of bootloaders, firmware, and other essential software. While the storage industry has seen significant advances, code storage has unique requirements that set it apart from general-purpose data storage. This article examines the current state of code storage, its challenges, and potential future developments.THE CURRENT LANDSCAPE OF CODE STORAGEMost code storage applications typically require capacities under 1 Gb. Bootloaders and firmware, for instance, often require at most 128 Mb. In contrast, the overwhelming majority of data storage today relies on 3D NAND Flash, which stacks memory cells in up to over 200 layers, each cell storing multiple bits using TLC (3-bit) or QLC (4-bit) technology. However, despite its efficiency for near Tb-scale storage, 3D NAND is not well suited for small-scale code storage, as a single layer already exceeds 1 GB capacity. For neither sub-1 GB code storage, NOR Flash remains the most common solution due to its low cost, high reliability, fast read speeds, and execute-in-place (XiP) capability. These advantages make it ideal for embedded systems, where fast and direct execution is necessary. However, NOR Flash has its limitations. When approaching 1 GB or higher capacities, it becomes expensive due to larger chip area requirements. Its scaling is constrained by channel hot electron injection, which limits gate lengths to above 100 nm.For applications requiring more than 1 GB but still negligible compared to general data storage, 2D NAND Flash is often used as a cost-effective alternative. 2D NAND benefits from its smaller cell size because it relies on Fowler-Nordheim tunneling rather than hot electron injection. However, NAND Flash has a fundamental drawback for code storag it does not support XiP, meaning code must be copied into DRAM before execution.As storage needs increase further, beyond 128 GB, 3D NAND becomes the dominant solution, offering the required density and scalability. However, the lack of XiP remains a fundamental limitation.Potential Disruptor: Faster, Low-Voltage Nonvolatile Memories New types of nonvolatile memory, including magnetic RAM (MRAM), resistive RAM (ReRAM), phase change memory (PCM), and ferroelectric RAM (FeRAM), offer potential advantages over Flash memory, such as higher speed and lower operating voltage. These technologies THE FUTURE OF CODE STORAGEBY FREDERICK CHEN, SR. TECHNOLOGY MANAGER - ADVANCED TECHNOLOGY DEVELOPMENT, WINBOND
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