Leibson's Law

NAND Flash manufacturing cost reductions of 60% per year sustained over nearly a decade have driven many technology changes, developments, compromises, and innovations. Prices have fallen even faster over the past five years, but the precipitous price decline could easily slow due to technical forces and in all likelihood, they will. Further, NAND Flash specifications are changing and will continue to change in predictable and unpredictable ways due to these forces. These changes will create new capabilities for NAND users, will impose extra performance burdens, and may ultimately limit the flexibility of NAND Flash in future device generations compared to what is available today.

This paper describes these trends in a series of warnings, enumerates the steps the semiconductor industry is taking to smooth product transition for NAND Flash users, and highlights developments that may create problems for NAND Flash users in the immediate future. NAND Flash trends discussed in this paper include:

• Page-size trends and their impact on NAND devices and controllers
• Changes to the spare area on NAND Flash devices
• Changing page architectures and ways to use the new architectures
• Increasing bit error rates and the associated rise in error correction code (ECC) complexity

NAND Flash manufacturers employ a broad variety of technology roadmaps, semiconductor implementation methodologies, and cost/performance optimization-and-tradeoff strategies to develop and manufacture NAND Flash devices. Diverse applications for NAND Flash memories drive similarly diverse performance specifications and requirements. "One Technology Roadmap Does Not Fit All" is an important guiding principle here. Consequently, products from some NAND Flash vendors may take somewhat different approaches to those described in this paper even though the vendors are responding to the same technical and market pressures considered below.

NAND-Flash controller designers may find the warnings and comments in this paper useful as they analyze important trends in NAND Flash management. In particular, advanced NAND Flash devices need extensive software management and error-correcting methodologies to create fully-functional memory subsystems that provide error-free data storage and they'll need even more management and better ECC methodologies in the near future. From Denali. http://j.mp/tAjUo