SanDisk may have just concluded a multibillion-dollar patent licensing lawsuit with Samsung which could determine the future of both SanDisk and the flash industry at large. As SanDisk considers a $5.8 billion takeover offer by the flash giant, private arbitration has given Sandisk rights to a technology that may well hold the future of flash memory, the Wall Street Journal reported Monday.
But first, a little technical background. Flash memory stores information in the voltage levels of floating gate transistors and is nonvolatile because those levels do not require power to maintain. Traditionally, digital information storage, including SRAM, DRAM, and early Flash, stored information by toggling each cell between two states; a neutral and a charged state; this is a single-level cell, or SLC, design. In what has heretofore been referred to as multi-level cell (MLC) flash, each cell has a neutral voltage and three levels of charged state, for a total of four states capable of storing two bits of information. While this scheme allows more data storage per transistor—and is hence much cheaper—reading 
more finely differentiated voltages requires finer measurement, which is in turn slower and more error-prone. It also reduces the usable life of the Flash thus produced. So SLC has been deemed superior in terms of performance and lifecycle, but MLC has been catching up and is currently dominating the rising SSD segment.
The Samsung versus SanDisk story centers on technology patents from a small Israeli company called M-Systems. M-Systems released some of the first NAND flash drives for use in rugged industrial and military computers, the onboard systems for the Israeli Defense Force tanks and aircraft. A number of years ago, M-Systems invented techniques that allow even finer voltage level setting and measurement in NAND cells, allowing them to store three bits (eight levels) or even four bits (16 levels) per flash cell. Referred to as X3 and X4 technology, this technique holds the promise of reducing flash costs still further.
Although the digital revolution is ultimately based on the accuracy and speed with which distinctions between only two voltage levels can be discerned, flash memory need not be as fast nor as durable as other forms of semiconductor products. In addition, the operating voltages of flash are much higher than those of DRAM, making more voltage levels feasible in each cell with the same voltage drop between levels. The cost advantages of current MLC technology are quite significant versus SLC, while its speed, longevity, and reliability difficulties are undergoing rapid improvement. As technology advances, it is reasonable to expect X4 technology to attain the same advantages over MLC that MLC now has over SLC. So X4 may well be the future path for the industry.
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