AUSTIN, Texas Motorola Inc. will demonstrate a non-volatile 1-Mbit magnetoresistive RAM test chip with 50-nanosecond access and program times at this week's VLSI Circuits Symposium in Honolulu.
In several key respects, the MRAM uses a more-advanced technology than earlier Motorola test chips with 256- and 512-kbit densities. It retains the one-transistor/one-magnetic-tunnel-junction (MTJ) structure but integrates copper wiring, a necessary step because MRAMs in future system-on-chip devices will be embedded with controller cores incorporating copper interconnects.
Saied Tehrani, director of MRAM technology in Motorola's Semiconductor Products Sector (Phoenix), said his group added a highly permeable, soft ferromagnetic cladding layer to the copper wires, which focuses the magnetic flux generated by the current flowing through the copper wires. The cladding directs the magnetic field toward the magnetic tunnel junction, helping cut power consumption by a factor of two, he said.
The cladding layer called a flux concentrator also focuses the generated magnetic field over the target cell, reducing crosstalk during programming.
Tehrani said the chip has an improved reference cell, which generates a signal midway between the maximum and minimum resistances. The improved reference cell cuts the per-bit power consumption in half, which, together with the flux concentrators, results in a 4x overall improvement in power consumption.
Motorola's commercialization plans for magnetoresistive random access memory call for sampling next year and early product introductions in 2004.
If all or even most of the claims for MRAM pan out, the technology eventually could displace other forms of embedded memory, including embedded DRAM and SRAM, flash, and ferroelectric (FeRAM) memory, Tehrani said.
MRAM's attributes span several of today's dominant memory types, leading Motorola to call it "the universal memory." The first products to adopt MRAM will use it to replace several conventional types of memory, such as in the stacked packages of SRAM, flash and DRAM die, used in leading-edge cellular phones. Or it could replace large blocks of flash.
"MRAM has the ability to read data very quickly, but it also can be programmed much faster than flash. And it can be programmed an unlimited number of times. We see it initially being used in systems with multiple types of memory," he said.
The access time for the 1-Mbit chip fabricated in a 0.6-micron process is about 50 ns, which may improve to 10 ns in a 0.18-micron process, he said.