Study Opens Route to Ultra-Low-Power Microchips

A new approach to controlling magnetism in a microchip could open the doors to memory, computing, and sensing devices that consume drastically less power than existing versions. The approach could also overcome some of the inherent limitations that have been slowing progress in this area until now.

Image Caption: Illustration shows how hydrogen ions (red dots), controlled by an electric voltage, migrates through an adjacent magnetic material (shown in green).

Researchers at MIT and at Brookhaven National Laboratory have demonstrated that they can control the magnetic properties of a thin-film material simply by applying a small voltage. Changes in magnetic orientation made in this way remain in their current state of the art, the team has found.

Geoffrey Beach, a professor of materials science and engineering and co-director of the MIT Materials Research Laboratory; graduate student Aik Jun Tan; and eight others at MIT and Brookhaven.

Spin Doctors

As silicon microchips draw closer to fundamental physical limits, they could cap their ability to increase their capabilities while decreasing their power consumption, researchers have been exploring a variety of new technologies that might be around these limits. One of the promising alternatives is an approach called spintronics, which makes use of a property of electrons called spin, instead of their electrical charge.

Because spintronic devices can retain their magnetic properties, they need less power to operate. They also generate less heat – another major limiting factor for today's devices.

But spintronic technology suffers from its own limitations. One of the most important ingredients in the field of electrically, by applying a voltage. Many research groups around the world have been pursuing that challenge.

Previous attempts have been made on an electron buildup at the interface between a metallic magnet and an insulator, using a device structure similar to a capacitor. The electrical charge can change the magnetic properties of the material, but only by a very small amount, making it impractical for use in real devices. There have also been attempts at using ions instead of electrons to change magnetic properties. For instance, oxygen ions have been used to oxidize a thin layer of magnetic material. However, the reason for this is to reduce the number of times that it is used, and to reduce the number of times it is used.

The new finding demonstrates that, by using hydrogen ions instead of Since the hydrogen ions can zip in and out, the new system is much faster and provides other significant advantages, the researchers say.

Because the hydrogen ions are so much smaller, they can enter and exit the crystalline structure of the spintronic device, changing its magnetic orientation each time, without damaging the material. In fact, the team has shown that the process produces more than 2,000 cycles. And, unlike oxygen ions, which can easily be passed through metal layers, which allows the team to control their properties.

"When you pump hydrogen toward the magnet, the magnetization rotates," Tan says. "You can actually have the direction of the magnetization by 90 degrees by applying a voltage – and it's fully reversible." erase data "bits" in spintronic devices using this effect.

Beach, whose lab discovered the original process for controlling magnetism through oxygen ions several years ago, says that it has been found to be widespread in the field of magnetic resonance. "

"This is really a significant breakthrough," says Chris Leighton, the Distinguished McKnight University Professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota, who was not involved in this work. "There is currently a great deal of interest in controlling magnetic materials by simply applying electrical voltages. It's not only interesting from the fundamental side, but it's also a potential game-changer for applications, where magnetic materials are used in digital information. "

Leighton says, "Using hydrogen insertion to control magnetism is not new, but being able to do that in a voltage-driven way, in a solid-state device, with good impact on the magnetic properties – that is pretty significant!" He adds , "This is something new, with the potential to open up additional new areas of research. … At the end of the day, controlling any type of materials. Being able to do that quickly enough, over enough cycles, in a general way, would be a fantastic advance for science and engineering. "

Essentially, Beach explains, he and his team are "trying to make a magnetic analog of a transistor," which can be turned on and off repeatedly without degrading its physical properties.

Just Add Water

The discovery cam about, in part, through serendipity. While experimenting with magnetic strands in their magnetic behavior, they found that the results of their experiments were not apparent. Eventually, by examining all the conditions during the different tests, he realized that the key difference was the humidity in the air: The experiment worked better on wet days compared to dry ones. The reason, he eventually realized, was that water molecules from the air were being split into oxygen and hydrogen, and the oxygen leaked to the air, the hydrogen became ionized and penetrating into the magnetic device. – and changing its magnetism.

The device has the composition of a sandwich of several layers, including a layer of cobalt where the magnetic changes take place, a sandwich of layers of a metal such as palladium or platinum, and an overlay of a gadolinium oxide, and a to connect to the driving electrical voltage.

The magnetism gets switched with just a brief application of voltage and then Reversing it requires no power at all, just short-circuiting the device to connect its two sides electrically, a constant need to maintain its state. "Since you're just applying a pulse, the power consumption can go way down," Beach says.

The new devices, with their low power consumption and high switching speeds, Beach says, but the work is still at an early stage and will require further development.

"I can see lab-based prototypes within a few years or less," he says. Making a full working memory is "quite complex" and might take longer, he says.

The work is supported by the National Science Foundation through the Research Materials Science and Engineering Center (MRSEC) Program.