08 March 2014

Magnetic materials can make future computer processor more efficient

multiferroic material
Anyone who has ever taken the term “laptop” seriously can attest to the extraordinary amount of heat they produce when the processor is cranking away. Despite years of advances in processor design, there is still a lot of heat produced as a by-product of running a CPU. This is all wasted energy that could be used for more productive purposes, but first we need a new approach to microprocessor design. A team of UCLA engineers might have figured out a way to make integrated circuits far more efficient by using a class of magnetic materials called multiferroics.

The standard processors in your computer, phone, and even your TV rely on millions or billions of transistors packaged as an integrated circuit. A transistor is essentially a tiny electronic switch that, when chained together, act as logic gates (AND, OR, etc.) Directing current through a transistor involves a certain amount of inefficiency, resulting in heat generation and the loss of electrons. There’s really no way around that as long as you’re moving electrons from one place to another, and the problem only gets worse as more transistors are packed into smaller spaces. A multiferroic material sidesteps the issue using a phenomenon known as spin waves.

A multiferroic material can be switched on and off at will simply by applying alternating voltage. Doing so allows it to carry power from one point to another through the cascading spins of electrons rather than by actually moving them. This complex magnetic effect is called a spin wave bus, but you can think of it a bit like an ocean wave. The energy of the wave moves in toward shore, but individual water molecules don’t have to go anywhere they just move up and down as the wave passes.

Spin Wave Bus

The team actually designed a chip to test the ability of a multiferroic material to maintain a stable spin wave bus. The device used in this experiment consisted of a nickel-based film atop a piezoelectric substrate the piezoelectric layer is where the initial voltage was applied to generate the spin wave. Down the middle of the chip was a 5 micrometer wide ferromagnetic stripe where all the action took place (that’s the gold line across the middle of the image at the top, and the green strip in the diagram above). This stripe acted as a waveguide for the spin wave bus, directing power from one end of the circuit to the other without moving any electrons.

This approach was successful in generating a voltage-driven spin wave, though it’s still a long way from replacing regular charge currents. The team believes that the improved efficiency offered by a spin wave bus could one day make processors at least 1,000 times more efficient. That could allow for a new generation of devices that do more work while using less power and generating less heat. Perhaps there will come a day when you can leave a laptop on your lap without fear of grievous bodily injury thanks to spin waves.

Research paper: doi: 10.1063/1.4865916 - "Electric-field-induced spin wave generation using multiferroic magnetoelectric cells

University of California, Los Angeles


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