Materials for Magnetoresistive Random Access Memory

MRAM technology is based on the storage of data in stable magnetic states using devices that have a large magnetoresistance effect, so that the data can be read by determining the resistance of the device. MRAM is inherently nonvolatile and the magnetic states can be switched extremely fast and with no wear out. In this article, we review the fundamentals of MRAM technology, explain the innovations that have overcome barriers to commercialization, and describe areas where further innovation can advance the technology most significantly. The influence of key structural and magnetic properties of materials used in magnetic tunnel junctions, and optimization of those devices for read and write performance in memory arrays, is discussed in detail. The various approaches to writing data in MRAM arrays are described and compared, with emphasis on toggle MRAM, the type that is in commercial production, and on spin-torque MRAM, which shows great promise for future improvements in power and density. In the final section, we summarize recent demonstrations of advanced MRAM technology.

[1]  S. Takahashi,et al.  Lower-current and fast switching of a perpendicular TMR for high speed and high density spin-transfer-torque MRAM , 2008, 2008 IEEE International Electron Devices Meeting.

[2]  Etienne,et al.  Giant magnetoresistance of (001)Fe/(001)Cr magnetic superlattices. , 1988, Physical review letters.

[3]  S. Tehrani.  Status and Outlook of MRAM Memory Technology (Invited) , 2006, 2006 International Electron Devices Meeting.

[4]  S. Yuasa,et al.  Giant tunneling magnetoresistance up to 410% at room temperature in fully epitaxial Co∕MgO∕Co magnetic tunnel junctions with bcc Co(001) electrodes , 2006 .

[5]  E. Wohlfarth,et al.  A mechanism of magnetic hysteresis in heterogeneous alloys , 1948, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[6]  H. Berg,et al.  Interfacial phenomena related to the fabrication of thin Al oxide tunnel barriers and their thermal evolution , 2001 .

[7]  B. N. Engel,et al.  Fundamentals of MRAM Technology , 2002 .

[8]  J. Simmons.  Generalized Formula for the Electric Tunnel Effect between Similar Electrodes Separated by a Thin Insulating Film , 1963 .

[9]  Robert E. Fontana,et al.  Low-field magnetoresistance in magnetic tunnel junctions prepared by contact masks and lithography: 25% magnetoresistance at 295 K in mega-ohm micron-sized junctions (abstract) , 1997 .

[10]  M. Mentzer,et al.  Fabrication and characterization of a crosstie random access memory , 1982 .

[11]  Saied N. Tehrani,et al.  MgO-based tunnel junction material for high-speed toggle magnetic random access memory , 2006, IEEE Transactions on Magnetics.

[12]  A. Umerski,et al.  Theory of tunneling magnetoresistance of an epitaxial Fe/MgO/Fe(001) junction , 2001 .

[13]  Jagadeesh S. Moodera,et al.  Spin polarized tunneling in ferromagnetic junctions , 1999 .

[14]  V. Soares,et al.  Large tunneling magnetoresistance enhancement by thermal anneal , 1998 .

[15]  A. Pohm,et al.  Design of Curie point written magnetoresistance random access memory cells , 2003 .

[16]  S. Ikeda,et al.  2 Mb SPRAM (SPin-Transfer Torque RAM) With Bit-by-Bit Bi-Directional Current Write and Parallelizing-Direction Current Read , 2008, IEEE Journal of Solid-State Circuits.

[17]  M. Julliere.  Tunneling between ferromagnetic films , 1975 .

[18]  S. Le,et al.  A statistical study of magnetic tunnel junctions for high-density spin torque transfer-MRAM (STT-MRAM) , 2008, 2008 IEEE International Electron Devices Meeting.

[19]  Y. Huai,et al.  Observation of spin-transfer switching in deep submicron-sized and low-resistance magnetic tunnel junctions , 2004, cond-mat/0504486.

[20]  M. Nakayama,et al.  Spin transfer switching in TbCoFe∕CoFeB∕MgO∕CoFeB∕TbCoFe magnetic tunnel junctions with perpendicular magnetic anisotropy , 2008 .

[21]  D. R. Krahn,et al.  The design of a one megabit non-volatile M-R memory chip using 1.5*5 mu m cells , 1988 .

[22]  Jon M. Slaughter,et al.  Magnetic tunnel junction based magnetoresistive random access memory , 2004 .

[23]  J. Slaughter,et al.  High speed toggle MRAM with mgO-based tunnel junctions , 2005, IEEE InternationalElectron Devices Meeting, 2005. IEDM Technical Digest..

[24]  Jian-Gang Zhu,et al.  Spin valve and dual spin valve heads with synthetic antiferromagnets , 1999 .

[25]  I. N. Krivorotov,et al.  Spin-transfer effects in nanoscale magnetic tunnel junctions , 2004, cond-mat/0404002.

[26]  Berger.  Emission of spin waves by a magnetic multilayer traversed by a current. , 1996, Physical review. B, Condensed matter.

[27]  S. Ikeda,et al.  Effect of electrode composition on the tunnel magnetoresistance of pseudo-spin-valve magnetic tunnel junction with a MgO tunnel barrier , 2007 .

[28]  L. J. Schwee,et al.  The concept and initial studies of a crosstie random access memory (CRAM) , 1982 .

[29]  K. Yakushiji,et al.  Magnetization reversal by spin-transfer torque in 90° configuration with a perpendicular spin polarizer , 2006 .

[30]  J. Katine,et al.  Device implications of spin-transfer torques , 2008 .

[31]  H. Meng,et al.  Spin transfer in nanomagnetic devices with perpendicular anisotropy , 2006 .

[32]  A. Omair,et al.  A 4-Mb 0.18-/spl mu/m 1T1MTJ toggle MRAM with balanced three input sensing scheme and locally mirrored unidirectional write drivers , 2005, IEEE Journal of Solid-State Circuits.

[33]  J. Katine,et al.  Current-induced magnetization reversal in nanopillars with perpendicular anisotropy , 2006 .

[34]  D. C. Ralph,et al.  Magnetoresistance and spin-transfer torque in magnetic tunnel junctions , 2008 .

[35]  Young Chung,et al.  Resistance Drift of Aluminum Oxide Magnetic Tunnel Junction Devices , 2006, 2006 IEEE International Reliability Physics Symposium Proceedings.

[36]  Kinder,et al.  Large magnetoresistance at room temperature in ferromagnetic thin film tunnel junctions. , 1995, Physical review letters.

[37]  H. Goronkin,et al.  High density nonvolatile magnetoresistive RAM , 1996, International Electron Devices Meeting. Technical Digest.

[38]  J. Bass,et al.  Erratum: Excitation of a Magnetic Multilayer by an Electric Current [Phys. Rev. Lett. 80, 4281 (1998)] , 1998 .

[39]  Ralph,et al.  Current-driven magnetization reversal and spin-wave excitations in Co /Cu /Co pillars , 1999, Physical review letters.

[40]  M. DeHerrera,et al.  Intrinsic Reliability of AlOx-Based Magnetic Tunnel Junctions , 2006, IEEE Transactions on Magnetics.

[41]  W. Brinkman,et al.  Tunneling Conductance of Asymmetrical Barriers , 1970 .

[42]  A. Panchula,et al.  Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers , 2004, Nature materials.

[43]  M. Hosomi,et al.  A novel nonvolatile memory with spin torque transfer magnetization switching: spin-ram , 2005, IEEE InternationalElectron Devices Meeting, 2005. IEDM Technical Digest..

[44]  R. W. Dave,et al.  A 4-Mb toggle MRAM based on a novel bit and switching method , 2005, IEEE Transactions on Magnetics.

[45]  Jon M. Slaughter,et al.  Magnetoresistive random access memory using magnetic tunnel junctions , 2003, Proc. IEEE.

[46]  J. Slonczewski.  Current-driven excitation of magnetic multilayers , 1996 .

[47]  T. Schulthess,et al.  Spin-dependent tunneling conductance of Fe | MgO | Fe sandwiches , 2001 .

[48]  D. Ralph,et al.  Spin transfer torques , 2007, 0711.4608.

[49]  S. Yuasa,et al.  Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions , 2004, Nature materials.

[50]  S. Cardoso,et al.  Dynamic Thermomagnetic Writing in Tunnel Junction Cells Incorporating Two GeSbTe Thermal Barriers , 2006, IEEE Transactions on Magnetics.

[51]  Saied N. Tehrani,et al.  Thermally activated magnetization reversal in submicron magnetic tunnel junctions for magnetoresistive random access memory , 2002 .

[52]  P. Brown,et al.  Reliability of 4 Mbit MRAM , 2005, 2005 IEEE International Reliability Physics Symposium, 2005. Proceedings. 43rd Annual..

[53]  B. Dieny,et al.  Thermally assisted switching in exchange-biased storage layer magnetic tunnel junctions , 2004, IEEE Transactions on Magnetics.

[54]  Saied N. Tehrani,et al.  Recent developments in magnetic tunnel junction MRAM , 2000 .

[55]  Saied N. Tehrani,et al.  High density submicron magnetoresistive random access memory (invited) , 1999 .

[56]  S. Parkin,et al.  Magnetic tunnel junctions thermally stable to above 300 °C , 1999 .

[57]  J. Daughton.  Magnetoresistive memory technology , 1992 .

[58]  A. Pohm,et al.  Curie point written magnetoresistive memory , 2000 .

[59]  T. Daibou,et al.  Tunnel Magnetoresistance Over 100% in MgO-Based Magnetic Tunnel Junction Films With Perpendicular Magnetic L1$_{0}$-FePt Electrodes , 2008, IEEE Transactions on Magnetics.

[60]  T. Miyazaki,et al.  Giant magnetic tunneling e ect in Fe/Al2O3/Fe junction , 1995 .