Schematic drawing of the multiferroic tunnel junction of two polarization configurations. The red layer is the ferroelectric barrier and the green layer is the interface that undergoes metal-to-insulator as well as magnetic-phase transition when the barrier polarization is reversed. Credit: Li lab, Penn State University

New material interface improves functioning of non-silicon-based electronic devices

February 19, 2013

(—For the first time, researchers have designed a special material interface that has been shown to add to and to improve the functioning of non-silicon-based electronic devices, such as those used in certain kinds of random access memory (RAM). According to Qi Li, a professor of physics at Penn State University and the leader of the research team, the new method could be used to design improved, more-efficient, multilevel and multifunctional devices, as well as enhanced nanoelectronic components—such as non-volatile information storage and processing; and spintronic components—an emerging technology that uses the natural spin of the electron to power devices. The research has been accepted for publication in the journal Nature Materials.

Li explained that most modern-day electronic chips—integrated circuits that serve as the building blocks for semiconductor electronic devices such as solar cells, personal computers, and cell phones—use silicon transistors to process “logical states,” or the binary system of ones and zeros used by computers. This binary information is stored for fast access in RAM and also permanently in a magnetic form on hard disks. In this system, the numeral 1 can be understood as “on”—with a current of electrons flowing freely—and the numeral 0 as “off”—with a current blocked. However, in recent years, Li said, researchers in laboratories across the world have been experimenting with different, non-silicon materials that “can toggle between a multilevel state system and can bring the memory into logic operation,” and also function with greater speed and less power consumption than are possible with current technology.

Now, in a new research study, Li and her colleagues have designed and tested an alternative way of creating a device that is compatible with non-silicon technology and that combines into one device both an electronic and a magnetic junction. “Magnetic tunnel junctions—which include two magnetic metallic layers with a very thin insulator barrier in between—have been used for binary-state devices, such as magnetic random-access memories (MRAM). Tunneling itself is a quantum-mechanical effect,” Li said. “Our goal was to create a multifunctional device with improved function by adding what we call a ferroelectric-magnetic interface—a ferroelectric layer replacing the insulator barrier and a special interface layer, less than one nanometer thick, built into the device that acts to change from metal to insulator as well as from ferromagnetic to antiferromagnetic in response to the negative or positive charge polarization of the barrier.” Thanks to this interface and through a phenomenon called the tunneling electroresistance effect, Li said, “we have found that the binary-state resistance difference, or the 1/0 system, is enhanced by up to 10,000 percent. This device is considered a quaternary-state device because we have integrated ferroelectric tunneling—which can be used as a switch or memory—into magnetic tunnel junctions, a type of magnetic memory.”

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