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

Abstract

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.

Effect of new materials as under and cap layers on thermal stability of synthetic bottom spin valves

“…However, Ta-based SVs degrade relatively quickly at elevated temperatures due to interlayer diffusion [3]. In this study, we investigated the effect of a new TiAl [4] and amorphous ZrAl alloy films [5] as under-and capping layer on the thermal stability and interdiffusion behavior of synthetic bottom-SVs at elevated temperatures.…”

The formation of amorphous alloy oxides as barriers used in magnetic tunnel junctions

“…23 This degradation is often attributed to a lack of uniform interfaces and other defects as a result of the presence of columnar grain boundaries in the polycrystalline precursor metal films prior to oxidation. 24,25 Since a precursor metallic phase in the amorphous state has no grain boundaries, 22 it is reasonable to expect that a continuous thin layer of oxide would form when exposed to an oxidizing atmosphere, causing an improved performance of a MTJ. Indeed, Bae et al reported the initial oxidizing paths of the crystalline precursors were the grain boundaries and then through the grains, leading to the formation of nonuniform interfaces and other defects 26,27 as well as the partial oxidation of the ferromagnetic layer below the tunnel barrier layer before completion of the Al oxidation.…”

“…Indeed, Bae et al reported the initial oxidizing paths of the crystalline precursors were the grain boundaries and then through the grains, leading to the formation of nonuniform interfaces and other defects 26,27 as well as the partial oxidation of the ferromagnetic layer below the tunnel barrier layer before completion of the Al oxidation. 28 However, since an amorphous phase was found in Al-Zr alloys via different experimental techniques, 22,[29][30][31][32][33] we choose to use this binary as a model system for both theoretical and experimental investigations in the present study. We will first present a thermodynamic formulation to predict alloy compositions of Al-Zr with tendencies to form amorphous thin films when these films are prepared using rapid quenching techniques such as sputter deposition.…”

“…[8][9][10][11][12] Alternative materials have also been actively studied to improve the quality of the tunnel barriers. [13][14][15][16][17][18][19][20][21][22] Among them, some alloy oxides show attractive properties to be used as MTJ tunnel barriers. The superior performance of these alloy oxide barriers is attributed to the formation of an amorphous structure in the preoxidation state in addition to a relatively low-energy band gap.…”

Tunnel barrier fabrication on Si and its impact on a spin transistor

“…Both of these tunnel barriers have been shown to spin inject with TMRs greater than 50% for Al 2 O 3 and 40% for ZrO 2 or Al 2 O 3 /ZrO 2 mixtures [6][7][8].…”