The spintronics challenge – Microelectronic devices that exploit the spin of the electron

Microelectronic devices that exploit the spin of the electron as well as its charge promise to revolutionize the electronics industry. The challenge, as Tony Bland, Kiyoung Lee and Stephan Steinmüller describe, is to find a way of integrating semiconductors into such “spintronic” circuits

Eighty years ago theoretical physicists had a problem: they lacked a mathematical description of elementary particles that was consistent with the principles of both Einstein’s special theory of relativity and the newly formed theory of quantum mechanics. In 1927 Erwin Schrödinger had written down the quantum mechanical equation of motion for the electron, but this did not take into account the fact that electrons are relativistic particles. Troubled by this situation, Paul Dirac set about finding a solution.

The equation Dirac arrived at the following year was a mathematical tour de force, which predicted two totally unexpected physical phenomena. The first was the existence of antiparticles, which was proved in 1932 with the discovery of the positron (an anti-electron). The second was that the electron must have an intrinsic angular momentum or “spin” that has only two possible orientations in an applied magnetic field: aligned with the field, or “up”; and anti-aligned, or “down”.

The electron lies at the heart of the microelectronics revolution, where it is shuttled around in semiconductors (usually silicon) to allow transistors and other such devices to operate. Yet these devices — which underpin everything from microwave ovens to cosmological probes — only exploit the charge of the electron, while for 70 years following Dirac’s groundbreaking discovery the electron’s spin has largely been ignored by the device and semiconductor industry.

One reason for this is the phenomenal success in miniaturizing devices. For the last 40 years the number of transistors per unit area that can be etched onto a silicon chip — which, for example, governs the processing power of a computer — has doubled every 18 months, a trend known as Moore’s law. But we are now rapidly approaching the limit of how small and closely packed these transistors can become before the heat that they generate cannot be dissipated fast enough, or unwanted quantum-mechanical effects prevent them from functioning properly.

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~ by vascoteixeira on August 25, 2008.

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