As dimensions approach nanometer ranges, CMOS transistors are difficult to operate because of rising power dissipation of chips and the fall in a power gain of smaller transistors, soaring fabrication plant costs, and finally, quantum effects in silicon are predicted to bring about an end to the ongoing miniaturization of CMOS.
While electronics depend on the charge of electrons to generate the binary ones or zeroes of computer data, spintronics depends on the property of electrons called spin. Spintronic materials register binary data via the “up” or “down” spin orientation of electrons—like the north and south of bar magnets—in the materials. While electronics depend on the charge of electrons to generate the binary ones or zeroes of computer data, spintronics depends on the property of electrons called spin. Spintronic materials register binary data via the “up” or “down” spin orientation of electrons—like the north and south of bar magnets—in the materials.
Electron spin is one such effect that offers the opportunity to continue the gains predicted by Moore’s Law, by taking advantage of the confluence of magnetics and semiconductor electronics in the newly emerging discipline of spin electronics. Using either the spin in tandem with the charge or alone, spintronics has some advantages over conventional semiconductor electronics, including higher integration density, non-volatility, decreased power dissipation and faster processing speeds.
Spin electronics (also called spintronics, magnetoelectronics or magnetronics) is “A branch of physics concerned with the storage and transfer of information by means of electron spins in addition to electron charge as in conventional electronics.” Spin-based electronics focuses on devices whose functionality is based primarily on the spin degree of freedom of the carriers. This is in contrast to conventional electronics, which exploits only the charge of the carriers. Spin wave based devices, which utilise collective excitations of electronic spins in magnetic materials as a carrier of information, have huge potential as memory devices that are more energy efficient, faster, and higher in capacity.
In quantum mechanics, spin is an intrinsic form of angular momentum carried by elementary particles. “Spin is a purely quantum phenomenon roughly akin to the spinning of a child’s top or the directional behavior of a compass needle. The top could spin in the clockwise or counterclockwise direction; electrons have spin of a sort in which their compass needles can point either “up” or “down” in relation to a magnetic field,” explain Sankar Das Sarma. Spin therefore lends itself elegantly to a new kind of binary logic of ones and zeros. The movement of spin, like the flow of charge, can also carry information among devices.
One advantage of spin over charge is that spin can be easily manipulated by externally applied magnetic fields, a property already in use in magnetic storage technology. Less energy is needed to change spin than to generate a current to maintain electron charges in a device, so spintronics devices use less power. Another subtler (but potentially significant) property of spin is its long coherence, or relaxation, time—once created it tends to stay that way for a long time, unlike charge states, which are easily destroyed by scattering or collision with defects, impurities or other charges.
Spintronic devices generate little heat and use relatively minuscule amounts of electricity. Spintronic computers would require no energy to maintain data in memory. Spintronic devices based on spin flipping can provide the high switching speed of the order of picoseconds), and hence can overcome the operational speed barrier of CMOS-based devices. There are various kinds of spintronics devices and
They would also start instantly and have the potential to be far more powerful than today’s computers. The spintronic devices will find widespread application in civilian and military markets offering new generation of transistors, lasers and integrated magnetic sensors.
Spintronics provides high speed, high power lasers, lower threshold current, high-density logic, low power, electronic memory devices, optoelectronic devices. This technology is an immense source for polarized light that is circular.
Spin Valve with Giant Magnetoresistance based Memory
One spintronic device that currently has wide commercial application is the spin-valve. Most modern hard disk drives employ spin-valves to read each magnetic bit contained on the spinning platters inside. A spin-valve is essentially a spin “switch” that can be turned on and off by external magnetic fields. Basically, it is composed of two ferromagnetic layers (that is, permanently magnetized) separated by a very thin non-ferromagnetic layer. When these two layers are parallel, electrons can pass through both easily, and when they are antiparallel, few electrons will penetrate both layers.
Depending on the relative orientation of the magnetizations in the magnetic layers, the electrical resistance through the layers’ changes from small (parallel magnetizations) to large (antiparallel magnetizations). Thus, by measuring the total resistance of the spin valve, it is possible to determine if it is in a parallel or antiparallel configuration, and since this is controlled by an external magnetic field, the direction of the external field can be measured.
Since each bit in a hard drive either points in one direction or the other, their orientation can easily be determined with a device using this mechanism. Investigators discovered that they could use this change in resistance (called magnetoresistance, and “giant” because of the large magnitude of the effect in this case) to construct exquisitely sensitive detectors of changing magnetic fields, such as those marking the data on a computer hard-disk platter. These disk drive read/write heads have been wildly successful, permitting the storage of tens of gigabytes of data on notebook computer hard drives, and have created a billions of dollar per year industry.
The two significant examples of spintronic devices and technology are non-volatile magnetic memories (MRAMs) and semiconductor spintronics. A magnetoresistive random access memory ( MRAM ) chip is a bidimensional array of magnetoresistive devices with stable remanent states (0 and 1), integrated on a silicon complementary metal–oxide semiconductor (CMOS) circuit allowing to separately address each memory element.
Spin Transfer Torque Random Access Memory (STT-MRAM or STT-RAM) stores information in the magnetic state of Nano magnets, but it is electrically written and read. This combination allows fast-access, non-volatile information storage but with better scalability over traditional MRAM. It relies on the different spin directions of electrons to signal a binary one or zero. The STT is an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve can be modified using a spin-polarized current.
Magnetic Tunneling Junctions (MTJs)
Another type of magnetoresistance that is governed by similar quantum mechanical laws is being exploited as a better mechanism for a much more sensitive magnetic field sensor. Like GMR, tunneling magnetoresistance (TMR) in a multilayer junction filters one spin polarization over another depending on the orientation of an external magnetic field. However, the two technologies differ in their exact filtering mechanism.
In a magnetic tunneling junction (MTJ), the device which employs the tunneling magnetoresistance effect, two magnetic layers are separated by a thin insulating layer. If a bias is placed across the junction, electrons will tunnel through depending on the relative orientation of the two ferromagnetic plates.
TMR effect is larger than GMR effect by about a factor of 10. Currently, TMR MTJ sensors have been used in hard drives.
Spin Torque Effect
When a current of electrons passes through a magnetized ferromagnetic layer, it becomes spin polarized in one direction, much like the polarization of light through a filter. However, spin is the quantum mechanical analogue of angular momentum, and when a current of electrons gets spin polarized by a ferromagnet, a small transfer of angular momentum happens between the current and the magnet.
Classically, when the angular momentum of any object changes, it experiences a torque. Much in the same fashion, the moment of the ferromagnetic layer experiences a torque when polarizing the spins of a current. Thus, by sending a strongly polarized current through a magnetic layer with a moment in a different direction, it is possible to place a torque on the layer’s magnetic moment and change its direction. This changing of the moment by sending a polarized current is called the spin-torque effect, or spin-transfer switching.
Spin transfer switching is currently being looked at as an alternative method to write data in magnetic random access memory (MRAM). The spin-torque effect can also be taken advantage of in the design and realization of ultrahigh-frequency (RF) microwave devices such as frequency standard devices, DC to AC converters, microwave sources, antennas, and isolators.
Magnetic (spin) transistors
In an ordinary transistor, specifically an n-p-n type transistor, two n-type semiconductors are separated by a p-type semiconductor. Near the n-p-n junction, a gate controls the voltage across the p-type semiconductor. The problem with electrically-based transistors is their volatility. When power is shut off, the electrons in the p-type semiconductor are no longer confined to a single region and diffuse throughout, destroying their previous on or off configuration. This is the reason why computers cannot be instantly turned on and off. However, a new type of transistor may change all of this.
In a magnetic transistor, magnetized ferromagnetic layers replace the role of n and p-type semiconductors. Much like in a spin-valve, substantial current can flow through parallel magnetized ferromagnetic layers. However, if, say, in a three layer structure, the middle layer is antiparallel to the two outside layers, the current flow would be quite restricted, resulting in a high overall resistance. If the two outside layers are pinned and the middle layer allowed to be switched by an external magnetic field, a magnetic transistor could be made, with on and off configurations depending on the orientation of the middle magnetized layer. Magnetic (spin) transistors are good candidates for logic devices (spin-logic).
Spintronics based Quantum computer
A long-term and ambitious subfield of spintronics is the application of electron and nuclear spins to quantum information processing and quantum computation. Classical computers push electrons through devices which code information into binary states of ones and zeros. In contrast, quantum computers use laser light to interact with electrons in materials to measure the phenomenon of electron “spin.” These spinning electron states replace the ones and zeros used as the basis for traditional computers, and because they can exist in many spin states simultaneously, this allows for much more complex computing to be performed.
Scientists and engineers from the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (CQC2T), are developing a scalable quantum computer in silicon. They found that a single atom of phosphorus could be used to tightly hold an electron, which also carries a “spin” (like a tiny magnet) that could be used as a quantum bit. Once the systems are scaled up to a large number of qubits, Quantum computers shall be able to execute nontrivial quantum algorithms to simulate quantum systems efficiently, crack modern encryption codes, search through huge databases, as well as solve a wide range of optimization problems.
Spintronics realizes new terahertz sources
German physicists, along with international collaborators, have realised a new concept for the production of electromagnetic radiation using spintronic emitters. Taking the form of thin, multi-layered, metal films and using the spin property of the electron – as opposed to the more conventional semiconductor emitters, which use only the electron charge – Physicists from the Fritz Haber Institute in Berlin and Johannes Gutenberg-University in Mainz (JGU) have developed the pioneering method by isolating a single unified source of terahertz (THz) emission that could provide useful terahertz radiation over a range of frequencies.
Professor Matthias Kläui of the JGU said: “Using this property, we were able to show that it is possible to produce broadband emitters fully covering the 1‑to‑30‑THz range which are also cost efficient in terms of their industrial applications.” The spin of the electron as a quantum property has led to new developments in spintronics in recent years. The optimisation of emitter performance involved Kläui and his team screening numerous materials with varying compositions and geometries, and was augmented by the calculations of theorists at innovative technology development company Forschungszentrum Jülich.
Samridh Jaiswal, an associate of Kläui at Mainz University, added: “The new THz emitter resembles a photodiode or a solar cell: on illuminating the material with an ultrashort laser pulse, an ultrafast spin current is generated. This spin current is then converted to a charge current via the Inverse Spin-Hall effect. Consequently, a transmitter antenna radiates an equivalent electromagnetic pulse with frequencies in the terahertz range
New spintronics breakthrough paves the way to faster computing
Researchers have achieved all-electric control of the spin of electrons in a major breakthrough that brings much faster and more efficient spintronics-based computation closer than ever before. Because a spinning electrically charged particle like an electron has well-known magnetic properties, the most natural way to control electronic spin is to use ferromagnetic materials embedded in spintronic devices. This, however, makes the devices very bulky, which is clearly the opposite of the direction towards which technological progress is pushing.
Led by Dr. Debray, the UC team managed to control the spin of electrons traveling on a wire with an all electrical device for the very first time, reaching a milestone in this new and very promising field that is important mainly because it allows for much smaller spintronic devices to be built.
The team used an indium arsenide “quantum point contact,” a wire only a few hundred nanometers in length whose conductivity can be modified by regulating the voltages at its two ends. The asymmetry that comes from setting two different voltages at the two ends (gates) allows the electrons to become polarized as they enter the wire.
Spintronics breakthrough could lead to single chip for processing and memory
Spintronics is now the preferred technology for manufacturing fast solid state drives (SSDs). In SSDs, so-called “spin valves” harness the magnetic properties of electrons to detect data that is stored in magnetic bits; by contrast, data processing relies on streams of electrons flowing around circuits within a microchip.
Using flexible organic semiconductors, researchers at Queen Mary, University of London and the University of Fribourg have made a discovery that could lead to the simultaneous storing and processing of data on the same computer chip, bringing a dramatic improvement in power efficiency and reduced weight of electronic devices
The Queen Mary/Fribourg team showed that lithium fluoride (LiF), a material with an intrinsic electric field, can modify the spin of electrons transported through the spin valves. This proves that electric fields can manipulate a magnetically polarized current and could lead to computer chips that not only store data, but are capable of manipulating it as well.
The researchers shot muons – unstable subatomic particles – into layers of lithium fluoride and observed their behavior as they decayed, which offered information about the magnetic processes inside the material. Low-energy muons are unique in that they can be placed into a specific layer, making it possible to study the behavior of single layers independently.
“This is especially exciting, as this discovery has been made with flexible organic semiconductors, which are set to be the new generation of displays for mobile devices, TVs and computer monitors, and could offer a step-change in power efficiency and reduced weight of these devices,” said Dr. Alan Drew, who led the research efforts. While devices that combine electron charge and spin are conceptually straightforward, this is the first time researchers have shown it is possible to proactively control the spin of electrons with electric fields.
The spin properties of light could enable spintronics and photonics to co-exist in devices
Researchers at Purdue University have shown that there is a very simple rule that governs light spin and momentum locking. This is a universal property for all optical materials and nanostructures, which makes it potentially very useful for photonic devices. This universality is unique to light and does not occur for electrons. The researchers aim to use these spin properties of light to interface with spintronics so that we might use both photons and electrons in devices.
“In fact, the spintronics dream is a seamless integration of electronic, optoelectronic and magnetoelectronic multifunctionality on a single device that can perform much more than is possible with today’s microelectronic devices,” says Sharma.
Semiconductor Spintronic: Recent Breakthroughs
Researchers are creating numerous breakthroughs in the field including controlling the spin of electrons, manipulating single electrons independently, and the first plastic spintronic computer memory device.
Researchers from the University of Tokyo (Japan), Tokyo Institute of Technology (Japan) and Ho Chi Minh University of Pedagogy (Vietnam) have overcome a significant obstacle to the development of next-generation device technologies. The team has become the first to report growing iron-doped ferromagnetic semiconductors working at room temperature—a longstanding physical constraint.
But until now, ferromagnetic semiconductors have only worked under experimental conditions at extremely low, cold temperatures, typically lower than 200 K (-73oC), which is much colder than the freezing point of water, 273.15 K. Here, K (Kelvin) is a temperature scale which, like the Celsius (oC) scale, has 100 degrees between boiling (373.15 K = 100oC) and freezing (273.15 K = 0oC) of water.
Doping is the practice of adding atoms of impurities to a semiconductor lattice to modify electrical structure and properties. Ferromagnetic semiconductors are valued for their potential to enhance device functionality by utilizing the spin degrees of freedom of electrons in semiconductor devices
“Bridging semiconductor and magnetism is desirable because it would provide new opportunities of utilizing spin degrees of freedom in semiconductor devices,” explained research leader Masaaki Tanaka, Ph.D., of the Department of Electrical Engineering & Information Systems, and Center for Spintronics Research Network, University of Tokyo.
Potential applications of ferromagnetic-semiconductors include designing new and improved devices, such as spin transistors. “Spin transistors are expected to be used as the basic element of low-power-consumption, non-volatile and reconfigurable logic circuits,” Tanaka explained.
Breakthrough in spin wave-based information processing technology
While spin wave based devices are one of the most promising alternatives to current semiconductor technology, spin wave signal propagation is anisotropic in nature — its properties vary in different directions — thus posing challenges for practical industrial applications of such devices.
A research team led by Professor Adekunle Adeyeye from the Department of Electrical and Computer Engineering at the NUS Faculty of Engineering, has recently achieved a significant breakthrough in spin wave information processing technology. His team has successfully developed a novel method for the simultaneous propagation of spin wave signals in multiple directions at the same frequency, without the need for any external magnetic field.
Using a novel structure comprising different layers of magnetic materials to generate spin wave signals, this approach allows for ultra-low power operations, making it suitable for device integration as well as energy-efficient operation at room temperature.
“The ability to propagate spin waves signal in arbitrary directions is a key requirement for actual circuitry implementation. Hence, the implication of our invention is far-reaching and addresses a key challenge for the industrial application of spin wave technology. This will pave the way for non-charge based information processing and realisation of such devices,” said Dr Arabinda Haldar, who is the first author of the study and was formerly a Research Fellow with the Department at NUS. Dr Haldar is currently an Assistant Professor at Indian Institute of Technology Hyderabad.
This discovery builds on an earlier study by the team that was published in Nature Nanotechnology in 2016, in which a novel device that could transmit and manipulate spin wave signals without the need for any external magnetic field or current was developed. The research team has filed patents for these two inventions.
“Collectively, both discoveries would make possible the on-demand control of spin waves, as well as the local manipulation of information and reprogramming of magnetic circuits, thus enabling the implementation of spin wave based computing and coherent processing of data,” said Prof Adeyeye.
DARPA’s Semiconductor Technology Advanced Research Network (STARnet)
Semiconductor Research Corporation (SRC) and the Defense Advanced Research Projects Agency (DARPA) has launched a $194 million initiative, the Semiconductor Technology Advanced Research Network (STARnet) to help maintain U.S. leadership in semiconductor technology that is vital to U.S. prosperity, security and intelligence.
One of the six academic teams is Center for Spintronic Materials, Interfaces, and Novel Architectures (C_SPIN): C_SPIN hosted at the University of Minnesota focuses on magnetic materials, spin transport, novel spin-transport materials, spintronic devices, circuits and novel architectures and create the fundamental building blocks that allow revolutionary spin-based multi-functional, scalable memory devices and computational architectures to be realized.
“Without the nanoelectronics sector there would be no viable defence sector, and without defence, investment in nanoelectronics would not be feasible”, said Michael Sieber, EDA assisting one roundtable.
The Global Spintronics Market was valued at USD 303.8 million in 2020, and it is projected to be worth USD 4,558.5 million by 2026, registering a CAGR of 50.4%, during the period 2021-2026 . The spintronics market is in its nascent stage, in which a significant portion of the market is still highly dependent on researches and technological innovations. Moreover, the supply side of the market was affected at the initial phase of COVID-19 due to nationwide lockdown and factory closure across the world. However, the scenario expanded the scope of the market studied as the industries, like data centers and cloud computing, witnessed a massive surge in demand and adoption.
The spintronics market is at a nascent phase of development, with huge growth potential over the forecast period. There have been significant investments in research to develop suitable devices capable of being deployed across the world in a broad range of applications.
In recent years, spintronics has been extensively deployed in data storage devices, due to its faster data transmission capabilities and increased storage capacities, when compared to conventional storage devices. It is used to compress massive amounts of data into a small area, as an instance, approximately one trillion bits per square inch (1.5 Gbit/mm²) or roughly 1 TB data can be stored on a single-sided 3.5″ diameter disc.
There have been comprehensive experimental efforts to control the electron displacement over long distances, although maintaining electron spin coherence after transfer remains a challenge. Since individual electron spins can be displaced coherently over a distance of 5 µm, controlling the spin of electrons for long distances was a challenge for the industry.
Spintronics Market Segmentation
The spintronics market has been segmented based on type, application, and region.
By type, the Spintronics Market has been segmented into metal-based devices and semiconductor-based devices. Among these, the metal-based devices are segmented into giant magneto resistance-based device (GMR), tunnel magneto resistance-based device (TMR), spin-transfer torque device, and spin-wave logic device, and the semiconductor-based devices are segmented into spin diode, spin filter, and spin field effect transistor (FET).
By application, the Spintronics Market has been segmented into (electric vehicles, industrial motors, data storage, magnetic random access memory (MRAM), semiconductor lasers, spintronics couplers, magnetic sensing, and others.
One of the prominent applications of spintronics is in electric vehicles (EVs). This is primarily attributed to the crucial role played by spintronics sensors in enhancing the battery performance of the EV. Without an exact measurement of the remaining battery capacity, reliable information on the remaining distance that can be traveled will be hard to determine. Moreover, enhancing the precision of battery monitoring enables the ability to check the charge and discharge condition of the battery, which is essential to calculate the remaining battery capacity, and prevents conditions that deteriorate the battery cell, thereby providing increased battery life.
According to Consors Finanz Automobile Barometer 2019, 69% of consumers in Germany decide against buying an electric vehicle because they expect the battery to run out while driving on the road. To avoid such instances, automakers and transportation infrastructure companies offer services such as showcasing precise battery consumption estimates and providing information about service and parking areas where such vehicles can charge the battery. These efforts will increase as EVs spread, and the electricity supply infrastructure witnessed considerable development in the future. These factors are poised to significantly increase the usage of spintronic devices such as TMR sensors in electric vehicles.
Among several types of current sensors used for battery monitoring, a typical measuring method is a type called a closed loop. Closed-loop current sensors have a large core consisting of a coil to generate magnetic flux for sensing. This has given challenges so far, such as decreased flexibility in battery monitoring design and an inability to reduce vehicle weight.
In February 2020, such challenges were solved by a new closed-loop tunnel magnetoresistance (TMR) current sensor developed by TDK, wherein a coreless sensor is utilized. The TMR current sensor, into which the magnetism detecting section (consisting of a coil, TMR element, and resistor) and the application-specific integrated circuit (ASIC) are integrated as one package, can measure a large current of almost 1200 A with high-precision, with an error as small as less than 1% in a non-contact manner. Besides, its low power consumption and small size can contribute to realizing high-precision battery monitoring.
This technology helps in creating a prototype device which used in industry as a read head and a memory-storage cell is the giant-magneto resistive (GMR) sandwich structure which consists of alternating ferromagnetic and non-magnetic metal layers. Depending on the relative orientation of the magnetizations in the magnetic layers, the device resistance changes from small (parallel magnetizations) to large (antiparallel magnetizations). Spintronic technology in general holds promises for digital electronics. It has been tested in mass-storage components namely hard drives.
By region, the Spintronics Market has been segmented into North America, Europe, Asia-Pacific, and the rest of the world.
Some of the major players in this digital scent technology market include IBM Corporation, NVE Corporation, Plures Technologies, Quantum Wise, NVE Corporation, Organic Spintronics, Advanced Micro Sensors, and Everspin Technologies, Inc.
- August 2020- Spin Memory Inc. announced a new solution ‘Universal Selector Technology’ that will significantly improve the capabilities of existing and emerging memory technologies. It is a completely new way of designing dynamic random-access memory (DRAM), magneto resistive random-access memory (MRAM), Resistive RAM (ReRAM), and other emerging memory technologies.
- July 2020- Crocus Technology Inc. announced the launch of CT110, a high resolution, isolated, contact current sensor based on Crocus’ patented and unique TMR technology. The CT110 provides highly accurate current measurements over a wide operating temperature range in a miniature form-factor. The CT110 offers design simplicity, reduced circuit complexity, and inherent isolation.