Magnetic tunnel contact

Schematic structure of a magnetic tunnel resistor

A magnetic tunnel junction (engl. Magnetic tunnel junction MTJ), short MTK is a spintronisches component which the TMR effect exploited. This is a component consisting of two ferromagnets , which are separated by a thin insulator . If the insulating layer is thin enough (typically a few nanometers ), electrons can tunnel between the two ferromagnets .

construction

Modern magnetic tunnel contacts consist of several layers placed one on top of the other. In the core there are two ferromagnetic layers, the direction of magnetization of which can be switched by an external magnetic field. These ferromagnetic layers are separated by an electrically insulating oxide layer. There are also additional outer separating layers which increase the thermal stability of the magnetic tunnel contact. The individual layers are only a few atomic layers thin.

Clear description

With the help of an external magnetic field , the direction of magnetization of the two ferromagnetic layers can be controlled independently of one another. If the magnetizations are aligned in the same way, the probability that electrons tunnel through the insulator layer is greater than with opposing (anti-parallel) alignment. This allows the electrical resistance of the contact to be switched back and forth between two different resistance states ( and ). ${\ displaystyle \ left \ vert 0 \ right \ rangle}$ ${\ displaystyle \ left \ vert 1 \ right \ rangle}$

Since the magnetization is retained even without additional power supply, magnetic tunnel contacts are suitable for use in non-volatile memories .

Manufacturing

Magnetic tunnel contacts are manufactured using thin-film technology. Magnetron sputtering is used to produce layers on an industrial scale, but molecular beam epitaxy , laser beam evaporation , electron beam evaporation and ion beam sputtering are also used on a laboratory scale . The actual contacts are produced with photolithography .

Tunnel barriers made of magnesium oxide (MgO) have been developed since 2000. In 2009, CoFeB / MgO / CoFeB contacts achieved relative changes in resistance of up to 600% at room temperature; at 4.2 K even more than 1100%.

application

The read heads of modern hard disk drives today work on the basis of magnetic tunnel contacts. Corresponding magnetic tunnel contacts are also used as Hall sensors .

Magnetoresistive RAM (MRAM) uses magnetic tunnel contacts as a storage element. In the future, use in pure spintronic circuits is also conceivable.

Individual evidence

↑ Weisheng Zhao, Xiaoxuan Zhao, Boyu Zhang, Kaihua Cao, Lezhi Wang, Wang Kang, Qian Shi, Mengxing Wang, Yu Zhang, You Wang, Shouzhong Peng, Jacques-Olivier Klein, Lirida Alves de Barros Naviner, Dafine Ravelosona: Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy. In: Materials. January 12, 2016, accessed March 1, 2017 .

[materials16-1] Weisheng Zhao, Xiaoxuan Zhao, Boyu Zhang, Kaihua Cao, Lezhi Wang, Wang Kang, Qian Shi, Mengxing Wang, Yu Zhang, You Wang, Shouzhong Peng, Jacques-Olivier Klein, Lirida Alves de Barros Naviner, Dafine Ravelosona: Failure Analysis in Magnetic Tunnel Junction Nanopillar with Interfacial Perpendicular Magnetic Anisotropy. In: Materials. January 12, 2016, accessed March 1, 2017 .