1Basic Memory Device Trends Toward the Vertical

1.1 Overview of 3D Vertical Memory Book

This book explores the current trend toward building electronic system chips in three dimensions (3D) and focuses on the memory part of these systems. This move to 3D is part of a long trend toward performance improvement and cost reduction of memories and memory system chips.

Thirty years ago it was thought that if the chips could just be scaled and more transistors added every few years, the cost would continue to drop and the performance and capacity of the chips would continue to increase. The industry then struggled with the effect of scaling to small dimensions on the functionality and reliability of the memory technology. Along the way dynamic RAMs (DRAMs) replaced static RAMs (SRAMs) as the high-volume memory component. Twenty years ago the memory wall became the challenge. This gap in performance between DRAM memory technology and fast processor technology was solved by the clocked synchronous DRAM. Nonvolatile memories were developed. The quest for fast, high-density, nonvolatile memories became more urgent, so the NAND flash was invented, made synchronous, and became the mainstream memory component. Meanwhile the ability to integrate millions of transistors on scaled chips led to an increased effort to merge the memories and processors on the same chip. The many advantages of embedded memory on chip were explored and systems-on-chip became prevalent. Now systems-on-chip exhibit ...

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