Magnetic Memory Technology

Spin-transfer-Torque MRAM and Beyond

Denny D. Tang, Chi-Feng Pai

• Publisher: Wiley-IEEE Press
• Year: 2020
• ISBN:
  9781119562283
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

STAY UP TO DATE ON THE STATE OF MRAM TECHNOLOGY AND ITS APPLICATIONS WITH THIS COMPREHENSIVE RESOURCE

Magnetic Memory Technology: Spin-Transfer-Torque MRAM and Beyond delivers a combination of foundational and advanced treatments of the subjects necessary for students and professionals to fully understand MRAM and other non-volatile memories, like PCM, and ReRAM. The authors offer readers a thorough introduction to the fundamentals of magnetism and electron spin, as well as a comprehensive analysis of the physics of magnetic tunnel junction (MTJ) devices as it relates to memory applications.

This book explores MRAM's unique ability to provide memory without requiring the atoms inside the device to move when switching states. The resulting power savings and reliability are what give MRAM its extraordinary potential. The authors describe the current state of academic research in MRAM technology, which focuses on the reduction of the amount of energy needed to reorient magnetization.

Among other topics, readers will benefit from the book's discussions of:

• An introduction to basic electromagnetism, including the fundamentals of magnetic force and other concepts
• An thorough description of magnetism and magnetic materials, including the classification and properties of magnetic thin film properties and their material preparation and characterization
• A comprehensive description of Giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) devices and their equivalent electrical model
• Spin current and spin dynamics, including the properties of spin current, the Ordinary Hall Effect, the Anomalous Hall Effect, and the spin Hall effect
• Different categories of magnetic random-access memory, including field-write mode MRAM, Spin-Torque-Transfer (STT) MRAM, Spin-Orbit Torque (SOT) MRAM, and others

Perfect for senior undergraduate and graduate students studying electrical engineering, similar programs, or courses on topics like spintronics, Magnetic Memory Technology: Spin-Transfer-Torque MRAM and Beyond also belongs on the bookshelves of engineers and other professionals involved in the design, development, and manufacture of MRAM technologies.

1
Basic Electromagnetism

1.1 Introduction

This chapter introduces basic electromagnetism. Starting from the simple attractive (or repelling) force between magnets, we define magnetic field, dipole moment, torque, and magnetic energy and its equivalence to current. At the end, we give a few methods to calculate magnetic field from electric current and from magnetic pole on material surface.

1.2 Magnetic Force, Pole, Field, and Dipole

Since electrostatic phenomenon was studied earlier than magnetostatic one, magnetic phenomena were described in analogy to electrical phenomena. Magnetic pole was defined as the source of magnetic field and force. Magnetic poles exert magnetic force to each other, like electric charges. In centimeter‐gram‐second (cgs) units, the force is proportional to the strength of the magnetic poles, defined as

(1.1)

where r is the distance between two poles, the unit is cm, the force is F, and the unit is dyne. So far, the unit of the poles are not defined; however, the dimension of a pole is

. When the distance between the poles is 1 cm, one unit of p₁ exerts a 1 dyne force to a unit of p₂, and vice versa. Like in Coulomb's law, the force can be described as a magnetic field H, produced by pole p₁ and exerts on p₂. Thus,

(1.2)

where H is defined as

(1.3)

Thus, a magnetic field H of unit strength exerts a force of 1 dyne onto 1 unit of magnetic pole. The unit of the magnetic field in cgs unit is oersted (Oe). To get a feeling about the strength of magnetic field, the magnetic field at the end of a magnetic bar on the classroom whiteboard can be as high as 200–1000 Oe, while the earth magnetic field is smaller than 0.5 Oe.

In 1820, H.C. Oersted discovered that a compass needle could be deflected when electric current passes through a wire nearby the compass. That is the first time electricity is linked to magnetic phenomenon. Subsequent work...