The day may be coming soon when designers will no longer differentiate between volatile and nonvolatile memory. While still years away from making SRAM and DRAM obsolete, new technologies including ferroelectric and magnetoresistive random-access memory are entering the market, and they seem destined to change forever the way engineers look at system design.
For many years, memory manufacturers have improved upon the speeds and densities of memory devices. Yet while many gains have been made architecturally as well as in process terms, the delineations have not really changed much. Overall, there still are two types of memory—volatile and nonvolatile. Designers use both in PCs, cell phones, laptops and other embedded devices from which we boot
(nonvolatile) and initialize (volatile).
The dominant volatile SRAM or DRAM (or PSRAM) technologies are fast, dense and relatively low in cost. Several manufacturers have similar and compatible products. Nonvolatile memory falls into a few subcategories too. ROM is read-only, mask or one-time programmed. E2PROM is reprogrammed on a location-by-location basis and is ideal for individual parameters or small data blocks. Flash is /great for larger data sets, executable code and long parameter strings.
But rewritable nonvolatile memories (E2PROM and flash) have problems with write speeds and endurance. It takes nanoseconds to modify volatile memory locations. It takes microseconds, milliseconds or seconds to modify rewritable nonvolatile memory.
Worse, today's nonvolatile rewritable technologies wear out quickly if their contents are constantly changing. If it were possible to rewrite these nonvolatile memory technologies quickly without impacting their life expectancy, things would change. And this is what may be happening as several key players pursue activities and benchmarks in this area.
The oldest technology in use for this purpose is still making inroads. Ramtron International, which pioneered ferroelectric technology, last year introduced its largest part yet, at 256 kbits (www.eeProductCenter.com (article ID: 21800363). Ramtron has been leveraging this technology in other areas as well, such as microprocessor companion devices (www.eeProductCenter.com, article ID: 21401429 ) and smaller packaging for commonly used configurations (www.eeProductCenter.com, article ID: 55301248 ). The company also offers the smaller, 16-kbit version of its ferroelectric nonvolatile RAM (FM25L16) with an SPI serial interface.
Small cell, giant MR
But Ramtron is not the only kid on the block anymore. Major players are showcasing their achievements in this area. A collaboration last year between IBM Corp. and Infineon Technologies AG served notice that serious players were involved in exploiting this technology (www.eeProductCenter.com, article ID: 14100086 ). While only 128 kbits in density, the fruit of the partnership was the smallest-geometry cell fabbed to date that implemented spin-based giant magnetoresistive (GMR) nonvolatile memory cells.
IBM has been using GMR for disk drive read heads for several years, but this collaboration marked the first application of GMR for creating a unified general-purpose memory chip.
Freescale Semiconductor Inc. is another pioneer in GMR types of memory as well as other novel technologies. One of interest is the Silicon Nano Structures (Sonos) memory, which has already successfully yielded a 4-Mbit device (www.eeProductCenter.com, article ID: 17100130).
More recently, Fujitsu Ltd. made waves when it announced that its 1-Mbit ferroelectric RAM was in production (www.ee
ProductCenter.com, article ID: 54201299). Fujitsu showed with the 1-Mbit announcement showed that it understands the need for a unified type of memory.
What's more, Fujitsu says it has found ways of improving the FRAM using a 0.35-micron 1T1C cell technology. It is the first company to mass-produce a megabit-class FRAM.
Two developments announced just last month pushed nonvolatile technology further into the limelight. First, Renesas Technology Corp. announced MRAM technology for system-on-a-chip use (www.eeProductCenter.com, article ID: 55800776). Having fabricated the new technology on its 130-nanometer CMOS process, Renesas demonstrated high-speed operation (143 MHz) at or above a 1.2-V operating voltage. Extensive endurance testing showed no degradation after 1 trillion rewrites, according to the company.
Also last month, NEC Corp. and Toshiba Corp. disclosed that they had designed a new cell that halves power consumption during data writes and cuts the writing errors of their novel MRAM architecture (www.eeProductCenter.com, article ID: 55800786). This technology is going to be used to create high-speed and high-density devices, the companies said.