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There are essentially two competing memory-storage solutions for mobile consumer electronics--NAND flash and NOR flash. NAND flash is capable of higher density, with 8-Gbit single-die and higher levels in the multidie stacked packages available today. The increased density is vitally important, given the additional functionality being integrated into consumer products. NOR flash, for its part, offers Execute In Place, which allows applications to run from the memory rather than from the RAM.

Compared with NAND flash, the Mbit/millimeter-square rating for the latest generations of NOR flash falls between 2- and 4-Gbit single-level cell NAND flash devices and 1- and 2-Gbit multilevel-cell NAND flash. This rating gives NOR flash a competitive edge against the encroachment of NAND and OneNAND solutions.

The NOR flash market has seen some changes recently, according to iSuppli. Spansion displaced Intel as the leader in the NOR flash market by growing 25.6 percent in the past year. Intel and STMicroelectronics were ranked second and third, respectively, followed by Samsung, Silicon Storage Technology and others. Total NOR flash revenue rose from $7.86 million in 2005 to $8.49 million in 2006.

NOR flash is most commonly used in wireless and embedded applications, specifically in cell phones and automobiles. Typical designs are dual-die solutions with NOR flash and DRAM packaged together.

New, potentially lucrative revenue streams in consumer electronics applications are possible, however, as the density of NOR flash increases. With higher density, NOR flash can prolong the design traction in these applications. New uses also can be found in areas such as publishing and capturing content for music, video, games, e-books and GPS maps.

Smaller process lithographies must be reached if NOR flash is to continue to provide increased density to meet growing storage requirements. The implementation of smaller processes allows more die per wafer to be generated, reducing the overall cost. In addition, die sizes can be maintained while the density doubles.

Intel was the first vendor to introduce 65-nanometer NOR flash solutions with its Strataflash Cellular Memory last year (M18, part number PF48F6000 M0Y0BE). The device was built using Intel's ETOX X 65-nm process. Intel's 90-nm product was significantly redesigned and featured a new sensing architecture, which is more robust and allowed Intel to scale its designs faster. The 65-nm release is proof that the redesign at 90 nm--specifically the work on the sensing scheme--is yielding benefits already. Because Intel was able to maintain the same architecture moving from 90 to 65 nm, the devices are drop-in compatible, which will make the transition easier for cellular OEMs.

The next release was the Spansion 90-nm 1-Gbit MirrorBit (part number S29GL01GP12FAI01). While Spansion has not yet migrated to a 65-nm lithography, it was still able to reach a 1-Gbit density using 90-nm technology. Spansion is also coming out with its QuadBit solution. While MirrorBit can store 2 bits per cell, Quad-Bit can store 4 bits per cell.

Spansion said the 90-nm 1-Gbit device will have a die size of 47 mm². The company also has plans for a 2-Gbit device with a die size of 76 mm².

The latest entrant is from STMicroelectronics (part number M39P0R1080E4ZAD). A second company entering the 65-nm node gives OEMs more options when choosing a NOR flash memory solution. Compared with other devices analyzed, the ST part has the smallest die size, resulting in the highest Mbit/mm square rating.

NOR flash technology is generating a lot of interest, and is still considered the dominant flash technology for the handset and mobile market. Considering the ongoing growth of the cellular industry, it's clear why manufacturers continue to make process improvements to NOR flash. Spansion, in announcing its soon-to-be-released 65-nm MirrorBit, said it has already begun development of a 45-nm NOR flash.

Gregory A. Quirk is technical marketing manager at Semiconductor Insights (Ottawa), a leading technical analyst company focusing on microelectronics.