Hitachi tips STT-RAM, mulls memory spinoff

SAN JOSE, Calif. -- At the Symposium on VLSI Technology to be held in Honolulu, Hawaii, from June 15-17, Hitachi Ltd. is expected to provide more details about its spin-transfer torque RAM (SPRAM) technology.

Japan's Hitachi (Tokyo) is also mulling plans to spinoff its SPRAM R&D efforts into a new company, but no decision has been made.

SPRAM is a next-generation MRAM. MRAM is a memory that uses the magnetism of electron spin to provide non-volatility. The technology is said to have unlimited endurance, but to date, MRAM has proven difficult to manufacture in mass volumes.

Spin transfer torque random access memory (STT-RAM) technology is a second-generation magnetic-RAM technology that is said to solve some of the problems posed by conventional MRAM structures. Avalanche, Crocus Technology, Everspin, Grandis, Hynix, IBM-TDK, Qualcomm, Renesas, Samsung, TSMC, Toshiba and others are looking at STT-RAM.

Grandis Inc.--a developer of STT-RAM technology--recently updated its product roadmap with some ambitious efforts in mind: It hopes to replace DRAM, and eventually, NAND, with its next-generation MRAM.

In contrast, Everspin--a spin-off of Freescale Semiconductor Inc.--is positioning its 16-Mbit MRAM for the SRAM replacement, data retention and related markets.

Meanwhile, Hitachi and its partner, Tohoku University, refer to their STT-RAM technology as SPRAM, which has been in R&D since 2002. ''Multi-level-cell spin-transfer torque memory is formed with series-connected magnetotunnel junctions (MTJ),'' according to Hitachi. ''The series MTJs (with differently sized areas) have shown multi-level resistance due to the combination of their magnetization directions.''

The entities presented a paper on a 2-Mbit chip in 2007, followed by a 32-Mbit device last year. Last month, the entities reported SPRAM for 6F² and 4F² cell sizes, which are reportedly seen as a DRAM replacement.

''By using this scheme, the SPRAM can afford to accept the DDRx-SDRAM compatible interface, because the proposed scheme is (a) similar sequence to the DRAM operation,'' according to a recent paper.

At VLSI, Hitachi intends to take the next step, which is possibly a NAND replacement. ''SPRAM will truly cover the area of the NAND flash memory, file memory region with infinite number of writing cycles,'' according to Hitachi.

In its roadmap, Hitachi plans to devise a 16- and 64-Mbit device in 2012, and a 256-Mbit and 1-Gbit chip by 2015.

However, Hitachi will most likely not sell the device under its own name. For the most part, Hitachi exited the IC business several years ago. So, as a result, Hitachi is ''thinking about spinning off'' its SPRAM technology into a new company. The formulation of our production is being discussed,'' according to Hitachi.

Hitachi may end up competing against its own offspring. Ironically, several years ago, Hitachi and Mitsubishi spun-off their chip businesses into a company called Renesas Technology Corp. Japan's Renesas is developing MRAMs and STT-RAM, reportedly based on technology from Grandis Inc.

Recently, Renesas acquired NEC Electronics Corp., which is also developing its own MRAM. To date, however, Renesas and NEC have not combined their MRAM efforts.