First Look:

Hitachi, Renesas develop nonvolatile phase change memory 

By Hank Brineen
iApplianceWeb
(02/19/07, 1:54 AM GMT)

Tokyo, Japan -  Putting in a bid for the next nonvolatile universal memory for mobile and portable devices, Hitachi and Renesas have developed a 512-kbyte (4-Mbit equivalent) phase change memory module operating at a 1.5-V power supply voltage, which achieves 416-kbyte/sec high-speed write and read speeds with a 20-nanosecond1 access time.

The new memory device is targeted at uses with microcontrollers, which have become core components in various kinds of wired and wirelessly connected control and information devices ranging from industrial equipment to in-vehicle systems, home electronics, and mobile phones.

As products become more sophisticated, connected and versatile, the amount of information handled by these microcontrollers has been rapidly increasing. Therefore, these microcontrollers require higher levels of performance and density in on-chip nonvolatile memory for storing data and programs.

At the same time, phase change memory is becoming a promising candidate for next-generation on-chip nonvolatile memory due to its high endurance of write cycles, simple structure, and ease of fabrication.

Phase change memory is a type of nonvolatile memory that exploits two-phase changes in electrical resistance of a film caused by Joule heat, which is generated by a current — an amorphous state3 (high resistance) and a crystalline state (low resistance).

Using these differences in electrical resistance as “1” and “0” information, it performs storage and readout operations. Hitachi and Renesas Technology have previously developed a low-power-operation phase change memory that can be written with a 1.5-V power supply voltage and 100-μA current using tantalum pentoxide for the interfacial layer.

As the write voltage can be lowered compared with conventional on-chip nonvolatile memory, this memory offers advantages such as eliminating a need for a power supply circuit that generates a high voltage within a chip, helping to reduce the module size, and achieving a high level of density.

However, because the readout current is small, it is critical to have a memory array circuit technology that enables high-speed operation despite its small current.

To learn more, go to www.hitachi.com or www.renesas.com.

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