New discovery aims to improve the design of microelectronic devices

The research was published in ACS Nanoa peer-reviewed scientific journal whose cover appears on its home page.

Advances in computer technology continue to drive demand for high-performance data storage solutions. Spintronic magnetic tunnel junctions (MTJs)—nanostructured devices that use electron spin to enhance hard drives, sensors, and other microelectronic systems, including magnetic random-access memory (MRAM)—are promising alternatives for the next generation of memory devices.

MTJs have become essential non-volatile memory elements in products such as smart watches and mass-storage computers, offering promise for use in energy-efficient artificial intelligence applications.

Using an advanced electron microscope, the researchers looked at the nanopillars in these systems, which are incredibly small, transparent layers inside the device. The researchers ran a current through the device to see how it worked. As they increased the current, they could watch the device degrade and eventually die in real time.

“Real-time transmission electron microscopy (TEM) experiments can be challenging, even for experienced researchers,” said Dr. Hwanhui Yun, first author of the paper and a research assistant professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota. “But after dozens of failures and optimizations, they consistently produced working samples.”

From this, they discovered that over time, with continuous current, the device’s layers compress, causing it to fail. Previous studies have theorized about this, but this is the first time scientists have been able to observe the phenomenon. Once the device forms a “hole” (a squeeze), it is in the early stages of degradation. As the researchers added more and more current to the device, the device melted and burned out completely.

“What’s remarkable about this discovery is that we observed this burnout at a much lower temperature than previous studies had thought possible,” said Andre Mkhoyan, senior author of the paper and professor and Ray D. and Mary T. Johnson Chair in the University of Minnesota Department of Chemical Engineering and Materials Sciences. “The temperature was almost half what was previously expected.”

By taking a closer look at the device on the atomic scale, the researchers realized that the materials that are tiny have completely different properties, including melting points. This means that the device will fail completely at a completely different time than anyone has seen before.

“There is a great need to understand the interfaces between layers in real time under real operating conditions, such as current and voltage application, but no one has achieved this level of understanding before,” said Jian-Ping Wang, senior author of the paper and McKnight Distinguished Professor and Robert F. Hartmann Chair in Electrical and Computer Engineering at the University of Minnesota.

“We are very pleased to announce that the team has made a discovery that will have a direct impact on the next generation of microelectronic devices in our semiconductor industry,” Wang added.

Scientists hope that this knowledge will be used in the future to improve the design of computer memory units, which will translate into longer life and increased efficiency.

In addition to Yun, Mkhoyan and Wang, the team included Deyuan Lyu, a postdoctoral researcher in the Department of Electrical Engineering and Computer Science at the University of Minnesota, assistant professor Yang Lv, former postdoctoral researcher Brandon Zink and researchers from the Department of Physics at the University of Arizona.

This work was funded by SMART, one of seven nCORE Centers, a Semiconductor Research Corp. program sponsored by the National Institute of Standards and Technology (NIST); the University of Minnesota Grant-in-Aid; the National Science Foundation (NSF); and the Defense Advanced Research Projects Agency (DARPA). The work was completed in collaboration with the University of Minnesota Characterization Facility and the Minnesota Nano Center.