Summary
SanDisk Corporation has announced 64Gb 4-bits-per-cell (x4) single die flash memory chip using multi-level cell (MLC) technology that it has co-developed with Toshiba Corporation on 43nm process technology node. This announcement came at the ISSCC 2009 conference where SanDisk presented its 3-bits-per-cell (x3) flash memory last year, the winner of the 2009 Lewis Winner Outstanding Paper Award. This is an important announcement for the flash memory industry because of the challenges associated in making x4 flash memory: i) 4-bits-per-cell technology requires working with 16 voltage levels and presents significant challenges in noise, signal coupling, and floating gate issues, ii) it requires sophisticated controller hardware to carry out required signal processing for maintaining high write speed and enabling data retention, and iii) a much higher error rate requires large number of redundant bits to ensure effective error-correcting codes.
Analysis
The controller and flash memory chips are integrated on a multi-chip module (MCM) package to provide a cost-effective integrated solution with write performance of 7.8 MB/s that comparable to existing MLC technologies. As a result, as you go from 32Gb flash memory chip to a 64Gb chip, you are still working at the same speed.
While this clearly gives SanDisk technological advantage in the flash memory competition and a tool in fighting brutal declines in memory prices, there are significant challenges in getting this technology to ramp this to volume production for the same reasons mentioned as challenges earlier in this article. As a result, this technology helping turn around at SanDisk depends upon how quickly SanDisk can bring this to volume production keeping an eye on the economic challenges facing the entire semiconductor industry chain.
Another interesting development during the ISSCC 2009 has been the announcement of a resistive random access memory (RRAM), a non-volatile memory with the potential density of a flash memory and speed of a dynamic RAM (DRAM), by an Australian startup called 4DS. A number of global companies such as Sony, Sharp, Samsung, LSI, Panasonic, Hynix, Micron, and others have explored RRAM in the past. Ferroelectric RAM (FRAM), Magnetic RAM (MRAM), and RRAM along with some other technologies are competing in the race for ‘Universal Memory’ that combines the best attributes of static RAM (SRAM), DRAM, and Flash memory.
