As the decade closes, the major battleground in memory technology lies squarely with nonvolatile (NV) devices. Even as flash—the king of NV memory—continues adapting to increase its utility, challengers based on magnetic and anti-fuse technologies are rising to wrest away a growing number of applications. At the same time, market forces are eroding the profitability needed to fund further flash technology developments.
Despite its limitations, flash is the dominant nonvolatile-memory technology in both system and system-on-a-chip (SoC) designs. The industry addressed the cost and endurance issues by improving process technology and implementing wear-leveling algorithms. Designers have learned how to work around the relatively slow erase and write speeds when using flash for working system memory, and they’ve massively adopted flash for read-intensive applications such as program and parameter storage.
Flash is poised to continue increasing its dominance by taking over applications currently served by other NV technologies such as EEPROM. For instance, Silicon Storage Technology (SST) recently developed a serial quad I/O (SQI) NOR flash family that challenges serial EEPROM for configuration storage while providing a low-pin-count alternative to byte-wide flash for code storage.
Introduced in 2008 at 16-Mbit density, the 26VF016 SQI device will ramp to production early this year with density increases quickly following. According to Douglas Lee, SST’s vice president for memory products, the company expects to sample 32-Mbit devices in the first quarter of 2009 and 64-Mbit devices by the middle of the year.
Interface Expands Flash Applications
The SQI architecture helps address a growing trend suffered by high-integration processors regarding pad-limited I/O. With their four-pin multiplexed serial data interface, SQI devices make it possible to reduce the memory bus to six lines (Fig. 1). This reduction doesn’t compromise memory bandwidth, however. The devices can operate at clock rates to 80 MHz and offer a continuous burst read at more than 300 Mbytes/s—fast enough for processors to execute code in place and eliminate the need for buffer memory.
Flash memory is also becoming increasingly available with interfaces that allow it to replace hard-disk drives as system mass storage. According to Tahir Husain, manager for Internet computing at SST, using a solid-state drive instead of a memory card for mass storage helps eliminate the need for redesign as higher-capacity flash devices become available. Hussain notes that memory controllers often lag in their ability to handle density increases.
The NANDrive, though, is available in pin-compatible solid-state drives with memory capacity in a range from 128 Mbytes to 8 Gbytes. The company expects to introduce a 16-Gbyte product in 2009.
But despite such adaptations to expand their market, flash memory will face increasing threats to its dominance in the coming months. Analyst firm IC Insights says that reduced demand due to economic conditions and excess fabrication capacity are eroding flash prices. ABI Research also notes price erosion, predicting a 60% drop in average sales price (ASP) per megabyte. The resulting profitability reduction is creating upheaval in the industry, which may result in vendors pulling out of the market or being absorbed by larger rivals.
Flash memory is also seeing competition from rising new technologies. In applications where memory is seldom written to more than once, such as code or archive data storage, anti-fuse technologies are becoming significant alternatives. One reason is the high level of data security provided by anti-fuse memory.
According to Jim Lipman, marketing director at memory IP developer Sidense, most of the developers the company surveyed indicated that data security is a significant concern. Lipman stated that code intellectual property and digital-rights-management keys for stored media are two areas where data security is of particular importance.
Competing NV Technologies emerge
Anti-fuse memory is more secure than flash because of the extreme difficulty in extracting the programming pattern from an anti-fuse device. Electronic scanning can non-destructively identify the charge state of flash-memory cells, giving software pirates an opening they can exploit. Anti-fuse memory, on the other hand, will not yield its secrets without destructive vertical etching to expose the programmed links, a method that’s expensive, time consuming, and error-prone.
The main applications for anti-fuse memory technology, however, are as a replacement for flash in on-chip storage rather than in standalone devices. As an embedded memory, anti-fuse technology holds several advantages over flash, including reliable data retention at high temperatures and scalability to advanced semiconductor processes. Embedded flash, according to Lipman, is typically a generation or two behind the state-of-the art in process technology.
A rising technology that threatens to one day replace flash as the dominant NV memory for both embedded and standalone applications uses magnetism rather than charges or fuses to store information. Magnetic RAM (MRAM) has been slow getting off the ground, but has now entered the market and will become increasingly available in the next year and beyond.
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