A new spin on memory

Aug. 9, 2001
The world'sfirst half-metallic ferromagnet could revolutionize computer memory, say scientists at Johns Hopkins University, Baltimore. "Dynamic random-access memory (DRAM) in today's computers stores data in tiny capacitors.

The world’s first half-metallic ferromagnet could revolutionize computer memory, say scientists at Johns Hopkins University, Baltimore. “Dynamic random-access memory (DRAM) in today’s computers stores data in tiny capacitors. These capacitors leak electronic charge and need refreshing periodically to prevent data loss,” explains Chia-Ling Chien, professor of physics at the University. “In contrast, the new CrO2 magnetic random-access memory (MRAM) retains data without power.”

A CVD process grows thin films of the material into magnetic tunnel junctions consisting of an insulator sandwiched between two electrodes, say researchers doing the fab at Brown University and IBM. Modulating the magnetization orientation of each electrode causes the junction to switch between high and low electrical resistance (digital logic). It may also be possible to increase the high-resistance configuration to an insulator which should ease MRAM development. Single-crystal films of the material could also bring improved magnetic sensors for reading information from higher density computer hard drives.

The trick to MRAM and other related technologies involves harnessing electron spin. Emerging spintronic and magnetoelectronic devices manipulate both electron charge and spin. Most modern hard drives use giant magnetoresistance read heads, for instance. The spin of each electron behaves as a tiny magnet with north (up) and south (down). The percentage of electrons with spin up indicates spin polarization. Most magnets have about 40% spin polarization, though theorists 15 years ago predicted materials with 100% spin polarization were possible. Such half-metallic materials have only one spin band, hence the name. JHU scientists say the new CrO2 thin films are about 96% spin polarized.

Wireless matches wired speed
Wireless LANs based on the new 802.11b Ethernet standard are more cross-compatible and cost less than those built around earlier standards. But the equipment works at a maximum 11 Mbit/sec rate, slow compared to the 100 Mbit/sec rate of wired Ethernet. Now the wireless standard is closing the gap. Texas Instruments recently announced a reference design for a 100-Mbit/sec Ethernet-compliant, full-duplex wireless optical LAN.

Here, each LAN-connected PC contains an interface card to drive an external optical transceiver. An 850-nm infrared laser and photodetector in the transceiver aim at a ceiling or wall-mounted basestation. The basestation is fitted with a DSPdriven MEMS mirror that simultaneously tracks up to 24 transceiver infrared light signals. And it maintains the connection at distances to 50 m, even when the PCs are moved about, provided there is a clear line-ofsight path. This dedicated, switched point-to-point architecture is faster than competing systems that share multipoint connections such as IrDA (2 m at 16 Mbits/sec), HomeRF (50 m at 10 Mbits/sec), Bluetooth (30 m at 1 Mbit/sec), and others.

Though LANs are the primary focus, the technology is also suitable for short-range optical links between buildings, broadband "last-mile" connections to homes and businesses, and video feeds. The reference design and related components are expected sometime this year. For more information, visit: www.ti.com/sc/alp

Speedier silicon
Intel recently introduced the Pentium 4 1.7-GHz processor built with the latest 0.18-µm fab technology. The P4 is designed to handle high bandwidth jobs such as video, audio, and 3D graphics.

A combination of Intel Netburst Microarchitecture, a 400-MHz bus, and a 850 chipset with dual RDRAM banks, pushes throughput to 3.2 gigabytes/sec. Price: $352 in quantities of 1,000.

Information comes from Penton Media’s Peddie Report

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