Solving the selectivity problem in magnetic random access memories using configurations that form C-states

Anthony S. Arrott

doi:10.1515/ijmr-2002-0167

Article

Solving the selectivity problem in magnetic random access memories using configurations that form C-states

Anthony S. Arrott

Published/Copyright: February 12, 2022

Published by

Become an author with De Gruyter Brill

Author Information

From the journal International Journal of Materials Research Volume 93 Issue 10

Abstract

The selectivity problem in magnetic random access memory is caused by processing problems that are metallurgical in origin. In honor of the 70th birthday of Professor Kronmüller, who has made so many contributions to magnetism and metallurgy, a solution of the selectivity problem is presented in which the metallurgical problems are circumvented by the design of the patterned thin film element to make it insensitive to processing problems. The solution is theoretical, using micromagnetics, the limitations of which call for experiments to support the conclusions.

Keywords: Magnetic random access memory; Micromagnetics; Patterned thin film elements

Prof. Anthony S. Arrott 5026 Reno Road, Washington, DC, 20008, USA Tel.: +1 202 364 6044 Fax: +1 804 524 5439

Dedicated to Professor Dr. Helmut Kronmüller on the occasion of his 70th birthday

The author was introduced to the world of MRAM by Prof. Jing Shi at Motorola. He continued his work on MRAM at Honeywell, Inc. with Dr. X.-D. Zhu. The Center for Interactive Micromagnetics was established with Professor C. Stronach at Virginia State University with the support of the Air Force Office of Scientific Research through Dr. H. C. Weinstock. For the tools for micromagnetics, the author is indebted to Prof. M. Scheinfein whose program LLG Micromagnetic Simulator has been continually upgraded to keep pace with the improvements in micromagnetics, particularly those brought about by Prof. Weinan E and his collaborators at Princeton and New York Universities. Conversations with Dr. R. Koch of IBM have been most helpful. The ultimate debts in micromagnetics are to the late Prof. W. F. Brown, Jr., Prof. A. Aharoni and Prof. A. Hubert. Fortunately, the mantels of these men are still carried by Professor Kronmüller and his students.

References

1 One measure of the hype surrounding the activity in magnetic random access memories is that the insertion of “MRAM” into the “www.google.com” search box produces some 20 000 references.Search in Google Scholar

2 Motorola has patented a selection scheme using ferromagnetic resonance.Search in Google Scholar

3 Switching astroids and most of the concepts discussed here can be found in the book by A. Hubert and R. Schaefer, Magnetic Domains, Springer, Berlin (1998). 148–152 and 201–214.Search in Google Scholar

4 The author has measured more than 100 000 hysteresis loops in pseudo-spin valves of many shapes and sizes at Motorola and Honeywell. Because of the sensitivity of magnetoresistance to variations in the switching processes it is possible to connect the details of the processes to mental images from the results of micromagnetic calculations. Concepts such as thermal excitations, edge-soliton propagation, 360° walls, and end instabilities become everyday experiences. The study of minor loops is, perhaps, the most useful way of distinguishing among many possible interpretations of the magnetoresistance results.Search in Google Scholar

5 Jing Shi, Saied Terhani, MRS symposium on Patterned Magnetic Structures (1998).Search in Google Scholar

6 The generalization of the Stoner –Wolhfarth astroid follows if the relation between the average components of the magnetization, <M_x> and <M_y>, during the switching processes can be fit to a segment of the ellipse {(<M_x>-M_x₀)/M_x₁}²+{(<M_yM_y₀)/M_y₁}²=1 and the internal energy (the sum of the magnetostatic, exchange and anisotropy energies) along this path can be fit to E_int=A+B cos²θ_ε≡A+B{(<M_x-M_x₀)/M_x₁}².Over limited ranges of bias field this is quite accurately the case for switching in a given mode. If the mode changes with bias field, this no longer works.Search in Google Scholar

7 Prof. M. R. Scheinfein, now at Simon Fraser University, created and maintains the LLG Micromagnetics Simulator as a commercially available state-of-the-art package for design and characterization of MRAM bits as well as other technological applications of small magnetic devices.Search in Google Scholar

Received: 2002-05-20

Published Online: 2022-02-12

You are currently not able to access this content.

Articles in the same Issue

https://doi.org/10.1515/ijmr-2002-0167

Keywords for this article

Magnetic random access memory; Micromagnetics; Patterned thin film elements