Magnetic Memory: Fundamentals and Technology

by Denny D. Tang , Yuan-Jen Lee

• ISBN13: 9780521449649
• ISBN10: 0521449642
• Edition: 1st
• Format: Hardcover
• Copyright: 2010-06-07
• Publisher: Cambridge University Press

Summary

If you are a semiconductor engineer or a magnetics physicist developing magnetic memory, get the information you need with this, the first book on magnetic memory. From magnetics to the engineering design of memory, this practical book explains key magnetic properties and how they are related to memory performance, characterization methods of magnetic films, and tunneling magnetoresistance effect devices. It also covers memory cell options, array architecture, circuit models, and read-write engineering issues. You'll understand the soft fail nature of magnetic memory, which is very different from that of semiconductor memory, as well as methods to deal with the issue. You'll also get invaluable problem-solving insights from real-world memory case studies. This is an essential book for semiconductor engineers who need to understand magnetics, and for magnetics physicists who work with MRAM. It is also a valuable reference for graduate students working in electronic/magnetic device research.

Author Biography

Denny D. Tang is vice President of MagIC Technologies, Inc., and has over 30 years' experience in the semiconductor industry. After receiving his Ph.D. in Electrical Engineering from the University of Michigan in 1975, he spent 15 years at IBM T.J. Watson Research Center, Yorktown Heights, NY, 11 Years at IBM Almaden Research Center, San Jose, CA, and 6 years at Taiwan Semiconductor Manufacturing Company (TSMC). He is a Fellow of the IEEE, TSMC, and the industrial Technology Research Institute (ITRI).
Yuan-Jen Lee is a Senior Engineer at Magic Technologies, Inc., where he develops advanced magnetic memory technology. He received his Ph.D. from the National Taiwan University in 2003, after which he worked for ITRI, Hsinchu, Taiwan, developing toggle MRAM and spin-torque MRAM.

Table of Contents

Preface	p. ix
Acknowledgments	p. x
Basic electromagnetism	p. 1
Introduction	p. 1
Magnetic forces, poles and fields	p. 1
Magnetic dipoles	p. 2
Ampere's circuital law	p. 3
Biot-Savart Law	p. 5
Magnetic moments	p. 5
Magnetic dipole energy	p. 6
Magnetic flux	p. 7
Magnetic induction	p. 7
Classical Maxwell equations of electromagnetism	p. 8
Inductance	p. 9
Equation tables	p. 10
Homework	p. 11
References	p. 12
Magnetic films	p. 13
Origin of magnetization	p. 13
Russell-Saunders coupling	p. 16
jj coupling	p. 16
Introduction of magnetic materials	p. 17
Diamagnetism	p. 18
Paramagnetism	p. 20
Ferromagnetism	p. 23
Antiferromagnetism	p. 28
Ferrimagnetism	p. 30
Ferromagnet/antiferromagnet bilayer structure	p. 30
Intuitive picture in exchange bias	p. 31
Positive exchange bias	p. 33
Theories of exchange bias	p. 35
AFM domain wall model	p. 36
Random field model	p. 38
Interlayer exchange coupling in ferromagnet/metal/ferromagnet multilayer	p. 39
Ruderman-Kittel-Kasuya-Yosida interaction	p. 41
Néel coupling	p. 44
Micromagnetic simulation	p. 46
Anisotropy energy	p. 46
Exchange energy	p. 47
Magnetostatic energy	p. 47
Zeeman energy	p. 48
Homework	p. 48
References	p. 49
Properties of patterned ferromagnetic films	p. 51
Introduction	p. 51
Edge poles and demagnetizing field	p. 51
Demagnetizing factor of elliptic-shaped film	p. 52
Edge curling	p. 54
Magnetic domain	p. 55
Transition region between domains: domain wall	p. 55
Bloch wall and Néel wall	p. 57
C-state, S-state and vortex	p. 58
Magnetization behavior under an external field	p. 59
Magnetization rotation in a full film	p. 60
Magnetization rotation in a patterned film	p. 61
Magnetization switching	p. 62
Magnetization rotation and switching under a field in the easy-axis direction	p. 63
Magnetization rotation and switching under two orthogonal applied fields	p. 64
Magnetization behavior of a synthetic antiferromagnetic film stack	p. 68
Homework	p. 71
References	p. 72
Magnetoresistance effects	p. 74
Introduction	p. 74
Anisotropic magnetoresistance	p. 74
Giant magnetoresistance	p. 77
Tunneling magnetoresistance	p. 79
Giant tunneling magnetoresistance	p. 83
Tunneling magnetoresistance in perpendicular magnetic tunneling junction	p. 88
Homework	p. 89
References	p. 89
Field-write mode MRAMs	p. 91
Introduction	p. 91
Magnetic tunnel junction RAM cell	p. 93
Cross-point array	p. 93
1T-1MTJ cell	p. 94
Read signal	p. 95
Sense reference cell	p. 96
Sense amplifier	p. 98
Write bit cell with magnetic field	p. 100
Write-field conversion efficiency	p. 100
Write-line cladding	p. 101
Astroid-mode MRAM	p. 102
Switching-energy barrier of Astroid-mode write	p. 102
Write-error rate of a bit cell	p. 105
Write soft error rate of an array of memory cells	p. 105
Homework	p. 106
Solution to the write disturbance problem	p. 106
Toggle-mode MRAM	p. 109
Toggle-mode cell	p. 109
Switching of SAF free layer in toggle-mode write	p. 111
Energy diagram of toggle operation	p. 112
Write-current reduction	p. 116
Characterization method of MRAM chip write performance	p. 116
Thermally assisted field write	p. 118
Multi-transistor cells for high-speed MRAM operation	p. 119
References	p. 120
Spin-torque-transfer mode MRAM	p. 122
Introduction	p. 122
Spin polarization of free electrons in ferromagnets	p. 122
Interaction between polarized free electrons and magnetization-macroscopic model	p. 124
Spin-torque transfer in a multilayer thin-film stack	p. 126
Spin-transfer torque and switching threshold current density	p. 129
Switching characteristics and threshold in magnetic tunnel junctions	p. 131
Regimes of write pulse width	p. 132
Switching probability in the thermal regime	p. 133
Spin-torque-transfer switching under a magnetic field	p. 140
Magnetic back-hopping	p. 141
Reliability of tunnel barriers in MTJs	p. 143
SPICE model of MTJs and memory cells	p. 144
Memory cell operation	p. 146
I-V characteristics of STT memory cell during write	p. 148
Read and write voltage window of STT memory cell	p. 150
Sense signal margin	p. 151
Homework	p. 152
Write-to-breakdown-voltage margin	p. 152
Data retention and Eb extraction method	p. 153
Thermal stability of STT memory chip	p. 154
Homework	p. 155
Write-current reduction	p. 156
Nanocurrent-channel film-stack structure	p. 157
Double-spin-filter structure	p. 159
Perpendicular MTJ	p. 159
Direct observation of magnetization reversal	p. 161
References	p. 163
Applications of MTJ-based technology	p. 165
Introduction	p. 165
MRAM market position	p. 165
MTJ applications in CMOS SoC chips	p. 169
Embedded memory in logic chips	p. 169
Unbalanced MTJ flip-flop	p. 169
Non-volatile multiplexer	p. 172
MTJ data register	p. 172
System-on-chip power reduction	p. 173
Runtime reconfigurable electronic system	p. 175
References	p. 175
Unit conversion table for cgs and SI units	p. 176
Dimensions of units of magnetism	p. 177
Physical constants	p. 178
Gaussian distribution and quantile plots	p. 179
Weibull distribution	p. 181
Time-dependent dielectric breakdown (TDDB) of magnetic tunnel junction devices	p. 183
Binomial distribution and Poisson distribution	p. 185
Defect density and the breakdown/TMR distribution of MTJ devices	p. 187
Fe, Ni and Co material parameters	p. 189
Soft error, hard fail and design margin	p. 190
Index	p. 193
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