Effect of Zr concentration on the microstructure of Al and the magnetoresistance properties of the magnetic tunnel junction with a Zr-alloyed Al–oxide barrier

We studied the composition dependence of the microstructure of Al–Zr alloy films and the tunneling magnetoresistance (TMR) behavior of magnetic tunnel junctions (MTJ) with a Zr-alloyed Al–oxide barrier. A highly stable MTJ with a superior-quality 9.89 at. % Zr alloyed Al–oxide barrier was achieved with 39.5% TMR and a bias voltage of 711 mV at half (Vh) TMR. The microstructure of Al changed systematically from polycrystalline to single phase amorphous to duplex phases composed of an amorphous Al–Zr phase and a crystalline AlZr compound, probably Al3Zr, as the Zr concentration increased. The microstructure of the Al–Zr alloy before oxidation has a dominant effect on the TMR characteristics and MTJ stability. A single amorphous Al–Zr alloy (∼10 at. % Zr) film has superior surface uniformity; consequently, an ultrahigh-quality oxide barrier was formed after oxidation.