AIST Develops GMR Device for Spin Injection MRAM Based on Perpendicular Magnetization

Nov 9, 2007 18:31 Motoyuki Ooishi, Nikkei Electronics

Japan's National Institute of Advanced Industrial Science and Technology (AIST) developed a current-perpendicular-to-the-plane (CPP) GMR device.

The CPP GMR device is developed by combining the spin injection magnetization reversal (spin injection) method and perpendicular magnetization technology. AIST aims at developing an MRAM with a capacity of 1 Gbit. The new device was presented at 52nd Annual Conference on Magnetism and Magnetic Materials (MMM), an international conference on magnetic recording now being held in Tampa, Florida.

The CPP GMR device is a GMR device that passes the sense current in the perpendicular direction to the film surface. AIST employed Fe/PT laminated films for the free and pinned layers, respectively, and used Au for the spacer. The free and pinned layers leverage the perpendicular magnetization of magnetic layer.

The Fe/PT laminated films used in the free and pinned layers were both formed by alternately stacking Fe and Pt atoms one by one. The films were formed by ultrahigh vacuum deposition (MBE process).

AIST reportedly succeeded in making the free layer extremely thin, 1-2nm to be exact, by stacking the atoms one by one. The thin free layer thus formed resulted in a reduction of switching (write) current, AIST said. The current density at the time of switching is 1 x 10⁷A/cm².

According to AIST, the device has a Δ value (Eu/kT), an indicator of thermal stability, of 60 or higher. Here, Eu, k and T denote the energy of magnetic body, Boltzmann constant and temperature, respectively. When the Δ value of the device used in a nonvolatile memory exceeds 60, the device is considered to be capable of retaining data for 10 years.

According to AIST, the biggest factor for achieving the Δ value exceeding 60 is the adoption of the perpendicular magnetization.

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