Fabrication and Characterizations of Fe/NaCl/Fe Magnetic Tunnel Junctions

Abstract

The tunneling magnetoresistance (TMR) of magnetic tunnel junctions (MTJ) was discovered in the middle of the last century, and it has attracted many researchers’ attention and led to a revolution in the field of data storage and magnetic sensing technologies over the past two decades.

There are different methods of fabricating the magnetic tunnel junctions. The industry tends to use the sputtering method at room temperature, which is more time and cost effective. While in laboratories researchers tend to use high vacuum electron-beam deposition system or Molecular Beam Epitaxy system (MBE) to grow the layers at elevated temperatures to make them epitaxial.

The basic structure of the magnetic tunnel junctions has two ferromagnetic electrode layers separated by a thin insulation barrier layer. Currently most industry is using cobalt-iron alloys as the ferromagnetic electrodes and magnesium oxide as the insulation layer. The most famous and profitable industrial products with this technology are non-volatile data storage and readout devices used in magnetic random access memory (MRAM) and hard disc drives.

In this thesis, high vacuum electron-beam deposition system is used to grow Fe/NaCl/Fe magnetic tunnel junctions on Si (100). We found that epitaxial tunnel junctions were prone to pinholes and electrode oxidation which severely reduced tunneling magnetoresistance. The highest tunneling magnetoresistance achieved in this system was on polycrystalline tunnel barriers with a 0.7nm thin Mg layer insertion, the tunneling magnetoresistance of which was 22.3% at room temperature and 37.8% at 77K in liquid nitrogen.