The Future of Electronic Devices

Source: The Hitavada      Date: 10 Jul 2018 12:28:00



By dr kailash r nemade

The field of spintronics is outcome of the discovery of "giant magnetoresistance effect” in the late 1980. The giant magnetoresistance effect occurs when a magnetic field is used to align the spin of electrons, which results in significant change in the resistance of a material. Spintronics, or spin electronics is an emerging field of device engineering, in which electron spin properties instead of, or in addition to electron charge to carry information is exploit for device fabrication. Existing microelectronics with large-scale integrated circuits facing two main problems, first one is power consumption and another is interconnection delay. Spintronics is the hopeful solution with additional virtue such as high-speed capability, virtually unlimited durability, and low operation voltage as the same as logic circuits. In electronic devices, information is stored and transmitted by the flow of electricity in the form of negatively charged subatomic particles called electrons. The zeroes and ones of computer binary code are represented by the presence or absence of electrons within a semiconductor or other material. In Spintronics, information is stored and transmitted using additional property of electrons called spin. Spin is the intrinsic angular momentum of an electron, each electron acts like a tiny bar magnet, like a compass needle, that points either up or down to represent the spin of an electron. Electrons moving through a nonmagnetic material normally have random spins, so the net effect is zero. External magnetic fields can be applied so that the spins are aligned (all up or all down), allowing a new way to store binary data in the form of one’s (all spins up) and zeroes (all spins down).

Spintronics activity mainly retained in ferromagnetic materials above room temperature will potentially lead to a new generation of spintronic devices. A new generation of electronic devices like magnetic sensors, high-speed data couplers, and magnetic random-access memories are possible with the new generation of spintronic technology. The first spintronics device based on the metal oxide semiconductor technology was proposed and fabricated in 1989 by Suprio Datta and Biswajit Das of Purdue University.

The use of electron spin, in addition to charge, emerges with promising new class of devices such as polarized light emitters, chips that integrate memory and microprocessor functions, magnetic devices exhibiting gain, and ultra-low power transistors. Spintronics is highly promising as a key technology for fabrication of next generation devices. Spintronics enable to provide beyond CMOS solutions for the realisation of spin logic circuits in which logic gates acting on the spin process information coded and propagated by spin currents.

Spintronics based wireless communication is novel approach in the present communication system. The intensive development in spintronics technology suggests that the spin–torque nano– oscillator (STNO), owing to its small chip size and high tunability, can be a new solution not only for memory and radio–frequency devices, but also for wireless communication. Typically, spin–torque nano–oscillators (STNO) are compact having dimensions less than 100 nm, without an LC resonance tank because they are based on the spin–transfer torque on nano–magnetic structures. In STNOs, oscillation occurs around static equilibrium at Gigahertz frequencies, which can be tuned by choosing the material parameters and device structure. The STNOs have critical disadvantages such as lower output power and poorer spectral purity in comparison with LC voltage–controlled oscillators (VCOs). But this issue can be resolved by adopting direct modulation with binary amplitude shift keying (ASK) despite major drawbacks of STNOs. This modulation scheme enables us to demonstrate STNO–based wireless communication with a decent data rate at a distance between the transmitter (T) and receiver (R) of 1 m. There are two types of circuit structures for binary ASK modulation which do not use intermodulation; one is modulation by turning on and off the oscillator directly, and the other is the modulation by switching on and off the on–state oscillator to the antenna. The main advantages of this technology is provides near field communication with low power consumption, Low dc consumption at the micro-watt level, nano-sized dimensions and cost effectiveness.

The desire to build smaller, faster, cheaper electronics has prompted a number of researchers to try using the ‘spin’ of an electron in transistors. These ‘spintronic’ transistors could be highly energy-efficient than traditional transistors in a smaller space. In addition, in optoelectronic applications, LASER and light-emitting diodes (LEDs) that take advantage of the spin of electrons could increase the data-carrying capacity of light. Electronic systems that use the spin of an electron–a quantum mechanical property that comes in two varieties: up or down–would work similarly to today’s transistors but have several advantages. Presently, electrical current alone is responsible for the logic functions in circuits. Current flowing through a transistor represents a 1; the absence of current, a 0. If the spin of an electron could be controlled, a “spin up” electron could represent a 1, and “spin down” a 0. Unlike electrical current, spin can be maintained even if the power is off, and a spintronic circuit would use less power because a current wouldn’t need to be constantly applied. Hence, companies such as Freescale Semiconductor are exploring spin-based solid-state memory. A second advantage is that using spin can further increase the information-storing and transmitting capacity of electrons, effectively making microprocessors run faster. Recently, IBM introduced GMR sensors into the read head of the newest generation of its hard disk products. The ‘spin transistor’ invented in the early 1990s. The desired spins are injected into a normal metal by passing a current from the magnetic metal to the normal metal. The spin-injected current induces a local imbalance in the spin-up/spin-down ratio, which can be detected by a nearby magnetic film.

The research team behind the current study has now taken the first step towards transferring spin-oriented electrons between a topological insulator and a conventional semiconductor. They generated electrons with the same spin in gallium arsenide (GaAs), a semiconductor commonly used in electronics. To achieve this, they used circularly polarized light, in which the electric field rotates either clockwise or counter-clockwise when seen in the direction of travel of the light. The spin-polarised electrons could then be transferred from GaAs to a topological insulator, to generate a directional electric current on the surface. The researchers could control the orientation of spin of the electrons, and the direction and the strength of the electric current in the topological insulator bismuth telluride, Bi 2 Te3. This flexibility has, according to the researchers, not been available before. All of this was accomplished without applying an external electric voltage, demonstrating the potential of efficient conversion from light energy to electricity. Findings are significant for design of novel spintronic devices that exploit interaction of matter with light, a technology known as "opto-spintronics." IBM, Motorola and Honeywell all have research teams attempting to develop a robust technology to use these devices to produce very high-density memory products-comparable to dynamic random-access memory - at speeds approaching those obtainable in static random-access memory (SRAM), with fewer masking steps and lower power. Honeywell has already demonstrated a fully functional 16 KB GMR memory, made with underlying electronics that can withstand the high radiation environment of satellites required. IBM estimates that their devices will scale to densities greater than 50 GB.
(The author is Head & Assistant Professor, Department of Physics, Indira Mahavidyalaya, Kalamb, Yavatmal & can be contacted at [email protected])