MRAM (2)

1. MRAM (2)

2. Advantage MRAM have a longevity because of the very important number of reader/write cycles that they can bear. ( The write time is not clearly determined; it is reasonable that this time will be lower than 10 ns for addressing bit-memory. ) The commercial memories are in a constant competition for reducing bit memory size and increasing density. ( MRAM can satisfy this target because of the bit-memory matrix addressing structure. ) In this new kind of memory, a bit, “0” or “1”, is stored as the orientation of the magnetic moment in a small size thin film element, thereby, nonvolatile because no electric power is needed to maintain the memory state.

3. Comparison of a number of characteristics for different Random Access Memories

4. These two states will constitute the two binary states in MRAM devices.

5. A schematic drawing of the operating mechanism of a spin-valve memory element

6. MRAM device pseudospin-valve design magnetic tunneling junction design vertical CPP/GMR multilayer design

7. pseudospin-valve A schematic drawing of the pseudospin-valve memory elements in a memory array along with the xy grid of word lines and digital lines for providing magnetic field to address each individual memory element

8. magnetic tunneling junction A schematic drawing of the readout mechanism for a magnetic tunneling junction memory design

9. vertical CPP/GMR multilayer A schematic drawing of the readout mechanism for a vertical CPP/GMR multilayer design

11. Repeated experimental measurements of the magnetoresistance for a rectangular pseudospin-valve memory element (Courtesy of Dr. Saied Tehrani). The irrepeatability in the measurements is due to the nonrepeatable domain configurations in the element during switching

12. Micromagnetic simulation of the switching process for a rectangular NiFeCo thin .lm element 1 × 5 m and 20 nm thick. The initial remanent state contains no magnetization vortices Micromagnetic simulation of the switching process for a rectangular NiFeCo thin .lm element 1 × 5 m and 20 nm thick. The initial remanent state contains two residual magnetization vortices at the ends of the element

13. Calculated switching field as a function of element width for a NiFeCo thin .lm element with and without residual vortices in the initial remanent state. The element is 1 × 5 m and 20nm thick

14. Formation of a 360. domain wall during switching of a thin NiFeCo film element 0.2 × 2.5 m and 2 nm thick. The two rows of color pictures at each stage during switching represent the longitudinal and the transverse magnetization component, respectively

15. A simulated magnetization reversal process for a pseudospin-valve memory element of an “eye” shape. The width of the element is 0.2 m and the end-to-end length is 0.6 m. The color represents the longitudinal component of the magnetization. The magnetization in both the hard and the soft layers reverses virtually by rotating in unison

16. Calculated switching fields for single-layer magnetic elements of four different shapes at 0.1 m element width. The variation of the switching field across different shapes is more than 100%

17. Illustration of the ring-shaped magnetic memory element supporting the circular magnetization mode as a stable flux-closure con.guration. The bit line connecting multiple bits in series shows the current-perpendicular-to-plane (CPP) mode. A memory stack consists of at least two magnetic layers: a hard magnetic layer (for storing a memory state) and a soft magnetic layer (for the dynamic readout)

18. Simulated magnetization processes during switching for both a soft layer and a hard layer with the assistance of a word line current field. The presence of the outward radial magnetic field yields a virtually coherent magnetization rotation during switching. Such a switching mode is very robust and repeatable

19. 待續………

20. References The Micromagnetics of Magnetoresistive Random Access Memory Jian-Gang Zhu (1) and Youfeng Zheng (2) (1) Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh, Pennsylvania, USA jzhu@ece.cmu.edu (2) Headway Technology, Inc. Milpitas, California, USA Magnetic tunnel junction device with perpendicular magnetization films for high-density magnetic random access memory Naoki Nishimura,a) Tadahiko Hirai, Akio Koganei, Takashi Ikeda, Kazuhisa Okano, Yoshinobu Sekiguchi, and Yoshiyuki Osada Semiconductor Device Development Center, Canon, Inc., 3-30-2, Shimomaruko, Ohta-ku, Tokyo, 146-8501, Japan ~Received 27 November 2001; accepted for publication 17 January 2002! Domain configurations of nanostructured Permalloy elements R. D. Gomez,a) T. V. Luu, and A. O. Pak Laboratory for Physical Sciences, 8050 Greenmead Drive, College Park, Maryland 20740 and Department of Electrical Engineering, University of Maryland, College Park, Maryland 20742 K. J. Kirk and J. N. Chapman Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom Magnetization vortices and anomalous switching in patterned NiFeCo submicron arrays Jing Shia) and S. Tehrani Motorola Phoenix Corporate Research Laboratories, 2100 E. Elliot Road, Tempe, Arizona 85284 T. Zhu SSEC, Honeywell, 12001 State Highway 55, Plymouth, Minnesota 55441 Y. F. Zheng and J.-G. Zhu Department of Electrical and Computer Engineering, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213 ~Received 22 July 1998; accepted for publication 5 March 1999!