Researchers Create First Bipolar Magnetic Junction Transistor

Over the past 50 years, computers have gotten faster and smaller due to miniaturization of integrated circuits.  According to Moore’s Law, which states that the number of transistors that can be placed on an integrated circuit will double about every two years, these improvements should continue.

But soon, transistor size will reach atomic dimensions— a major barrier for scientists and engineers in the miniaturization of transistors.

One possible solution are magnetic semiconductor devices, which use electron spin to control conduction. Researchers at the McCormick School of Engineering and Applied Science at Northwestern University have created for the first time a bipolar magnetic junction transistor and that shows amplification and operation at room temperature.

Graduate student Nikhil Rangaraju, postdoctoral fellow John A. Peters, and Bruce W. Wessels, Walter P. Murphy Professor of Materials Science and Engineering, designed and created the device. Their results are published online in the journal Physical Review Letters.

Over the past 10 years, Wessels and his group have been working to create semiconductor alloys that are magnetic. He found it in thin films of the alloy Indium-Manganese-Arsenic, which Wessels previously used to create semiconductor diodes. Now that the group has created a transistor that uses the magnetization to control the amplification, they’ve created a semiconductor that is multifunctional: It can potentially process and store digital information. For example, in a computer, the hard drive that stores information is magnetic, while the semiconductor memory processes it. A semiconductor magnetic junction transistor could potentially do both jobs.

Researchers have previously created magnetic semiconductor devices, but Wessels and his group are the first to create one that can control spin and amplify signals at room temperature — two  operations essential to computer processing.

Creating this device has taken two years of microfabrication, characterizing, and measurement, which they performed at McCormick and at Argonne National Laboratory’s Center for Nanoscale Materials.

Potential immediate applications for the device include magnetic sensors (like the kind used in magnetic resonance imaging MRIs), and in the future, this device could be used as a basic building block for a new kind of computer logic.

Next researchers hope to improve the device performance and integrate it with other devices onto one chip.

“It’s almost like the holy grail of computer logic to get devices that show magnetism and semiconduction at the same time,” Wessels said. “Could this be an answer to the limits of Moore’s Law? We have hope.”