Low-resistance spin-dependent tunnel junctions with ZrAlOx barriers

Abstract

Spin-dependent tunnel junctions with ZrAlO x barriers were fabricated with low resistanceϫarea product 4 ⍀ϫ m 2 , and tunnel magnetoresistance of 15.2%. Barrier fabrication was done by natural oxidation ͑5 min, at oxidation pressures ranging from 0.5 to 10 Torr͒. The junctions were deposited on top of 600 Å thick, ion beam smoothed, low resistance, Al electrodes. X-ray photoelectron spectroscopy analysis indicates the presence of AlO x , ZrO 2 , some remnant metallic Zr, but no metallic Al in the as-deposited barriers. High resolution transmission electron microscopy indicates that ZrAlO x forms an amorphous barrier that is smoother than pure crystalline ZrO x or pure amorphous AlO x barriers. These low resistance tunnel junctions are attractive for read head applications above 100 Gbit/in 2 where competitive signal to noise ratios imply resistanceϫarea product below a few ⍀ϫ m 2 , and tunneling magnetoresonance signals near or above 20%.

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

“…5,8,9,[11][12][13] Among low-resistance barrier MTJs, a MTJ with a ZrAlO x barrier ͑thickness 0.7 nm͒, which was fabricated by inserting a Zr layer between Al/ ferromagnet layers, had low resistance and a moderate tunnelling MR ͑TMR͒ ratio ͑15.3%͒ after annealing, but it had a high bias-voltage dependence ͑210 mV͒. 11 In this letter, we investigate how microstructural changes of Al resulting from alloying it with Zr affect the quality of the tunnel barrier and the subsequent MR characteristics. Especially, we demonstrate that alloying Al with Zr enhances the TMR, and bias-voltage dependence of the MTJ in terms of the microstructural development of Al-Zr alloy films.…”

“…The most important characteristics that affect MTJ device performance are proper junction resistance, microstructural quality, and the stability of the tunnel barrier. Various oxidation methods, 1-4 new barrier materials, [5][6][7][8][9] and modified AlO x materials 10,11 have been used to complement these tunnel barrier characteristics. HfO 2 , 6 AlN, AlON, 7 Al/Hf/Al 10 have relatively high-quality tunnel barriers, but a small magneto resistance ͑MR͒ ratio or a high resistance.…”

TEM and EELS measurements of interface roughness in epitaxial Fe/MgO/Fe magnetic tunnel junctions

“…Most of the experimental and theoretical studies on MTJs have shown that the tunnel magnetoresistance ͑TMR͒ strongly depends on the atomic structure of the barrier and of the magnetic electrodes. This can clearly be seen from the comparison between polycrystalline and single-crystal MTJs: the tunnel magnetoresistance of the junctions which use a polycrystalline or an amorphous barrier [3][4][5][6] is indeed lowered by the low barrier height, the interface roughness, the difficulty to control the degree of oxidation throughout the amorphous insulating layer, 7 the magnetism of the polycrystalline ferromagnetic electrodes, and the complexity of the transport mechanisms across the disordered insulator. The situation is different for single-crystal oxide barriers grown in epitaxial orientation with respect to the magnetic films, for which recent calculations have predicted high TMR values.…”

Performance of Fe3O4/AlOx/CoFe magnetic tunnel junctions based on half-metallic Fe3O4 electrodes

“…Most of the experiments have been carried out by using ferromagnetic materials of Co, Ni, Fe, and their alloys as magnetic electrodes and an insulating Al 2 O 3 barrier [1][2][3]. Magentoresistance (MR) ratio of MTJ is given by…”