Annealing Effect on Low-Resistance Ferromagnetic Tunnel Junctions

Abstract

The stacking structure and fabrication process of tunnel junctions were investigated. The stacking structure of the tunnel junctions fabricated was Ta/(Cu,Pt)/Fe20Ni80/IrMn/Co75Fe25/Al-oxide/Co75Fe25/Fe20Ni80/Ta. When the Al thickness, oxidation time, and annealing temperature were 0.8 nm, 15 s (10 s), and 300°C (250°C), the tunnel magnetoresistance (TMR) ratio and the resistance obtained were 49% (31%) and 1.1 kΩµm2 (230 Ωµm2), respectively. In order to investigate the annealing temperature dependence of the TMR ratio, the local electrical properties were measured for a Ta/Fe20Ni80/Pt/Fe20Ni80/IrMn/Co75Fe25/Al-oxide multilayer. The current image became very homogeneous after annealing at around 300°C for 1 h. The increase of the TMR ratio of the junction after annealing can be well explained by taking into account both an increase of barrier height and a decrease of barrier height fluctuation. After further annealing at above 350°C, the barrier height decreased and leakage currents were detected.

Tunnel magnetoresistance with plasma oxidation time in doubly oxidized barrier process

“…The junction resistance, however, increased monotonically with increasing oxidation time. Similar behavior of tunnel junction was reported by other researchers in which the MR ratio peaked at an optimal oxidation condition while the junction resistance increased continuously with the oxidation time [13,14]. It is noted that even though the MR ratio started to drop due to probable over-oxidation of the first Al layer, the MR ratio is still greater than that of the junction with the maximum MR ratio of 24 % in the singly oxidized tunnel barrier [15].…”

Statistical properties of currents flowing through tunnel junctions

“…This type of experiments has been reproduced by several groups with similar results [10,11,12,13,14,15]. They are especially useful for barrier optimization, for instance with respect to oxidation [16,17] or annealing [13,18].…”

Microstructural observation on effect of oxidation method of AlOx in magnetic tunnel junction by high resolution transmission electron microscopy

“…3͑c͒ is shown by an arrow. It has been suggested that the oxygen will enter a metallic Al layer through the grain boundaries at an early stage of oxidation and diffuse into the grain afterwards 8 but it has not been verified in terms of oxide microstructures. Smith et al 9 also proposed the grain boundary diffusion as a possible mechanism for different barrier height in the oxide layer but their interest was in the crystalline or amorphous nature of the oxide layer.…”