Magnetoresistance device including layered ferromagnetic structure, and method of manufacturing the same

Abstract

A layered ferromagnetic structure is composed of a first ferromagnetic layer positioned over a substrate; a second ferromagnetic layer positioned over the first ferromagnetic layer; and a first non-magnetic layer placed between the first and second ferromagnetic layers. The top surface of the first ferromagnetic layer is in contact with the first non-magnetic layer. The first ferromagnetic layer includes a first orientation control buffer that exhibits an effect of enhancing crystalline orientation of a film formed thereon.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a magnetoresistance device, and more particularly relates to a magnetoresistance device having a structure where at least one of free and fixed magnetic layers is composed of a plurality of ferromagnetic layers separated by one or more non-magnetic layers. [0003] 2. Description of the Related Art [0004] Magnetoresistance devices, such as a memory cells of MRAM (Magnetic Random Access Memory) and magnetic heads of recording devices is often composed of a structure provided with a plurality of ferromagnetic layers whose neighbors are separated by a non-magnetic layer; such structure is referred to as the layered ferromagnetic structure, hereinafter. The layered ferromagnetic structure is designed so as to attain desirable functions by using exchange coupling between the adjacent ferromagnetic layers. [0005] One example of the applications of the layered ferromagnetic structure is the M...

AI Technical Summary

Benefits of technology

[0133] Alternatively, a highly-oriented crystalline MgO layer having the NaCl structure may be used as the tunnel barrier layer 5. The use of a crystalline MgO layer exhibiting high (001) orientation as the tunnel barrier layer 5 advantageously achieves a high MR ratio of the magnetic tunnel junction. It should be noted that the present invention causes its advantageous effects, regardless of the material and crystalline structure of the tunnel barrier layer 5.

Problems solved by technology

However, in the MRAM that uses a single-layered ferromagnetic film as the free magnetic layer, the increase in the volume of the free magnetic layer undesirably increases the magnetization and thickness product (namely, the product of the magnetic film thickness and the saturation magnetization) of the free magnetic layer. as the free magnetic layer.

The increase in the magnetization and thickness product of the free magnetic layer increases the magnetic field generated by the magnetization, and thereby undesirably causes the magnetic interference between adjacent memory cells.

Moreover, the increase in the magnetization and thickness product of the free magnetic layer makes it hard to reverse the magnetization of the free magnetic layer.

Achieving sufficiently great exchange coupling may be a problem, especially in the case where a layered ferromagnetic structure is formed on a tunnel barrier layer.

As a result, a ferromagnetic layer formed on the tunnel barrier layer often exhibits poor orientation.

This weakens the exchange coupling between the ferromagnetic layers, and prevents desired properties from being achieved in the layered ferromagnetic structure.

Such situation is especially severe when the ferromagnetic layers within the SAF are formed of NiFe.

It is hard to obtain sufficiently large exchange coupling between NiFe ferromagnetic layers within SAF.

In such situations, large exchange coupling is not obtained, which causes the same problem.

In many cases, crystal structures of SAF films are not well matched with that of the underlying crystalline tunnel barrier film.

Although there is a need for a technique that achieves improved crystal growth of SAF films regardless of the crystal structure the underlying tunnel barrier, no approach has been currently proposed.

Incorporating a layer structure composed of CoFe and NiFe films within each ferromagnetic layer of the SAF may achieve enhanced exchange coupling; however, the use of CoFe films results in the increase in the saturated magnetization and crystal magnetic anisotropy of the SAF.

However, the excessive increase in the exchange coupling energy J undesirably leads to the increase in the spin flop field Hflop.

This implies that the magnitude of the exchange coupling energy is not freely controllable by the thickness of the non-magnetic layer.

The disclosed SAF structure, however, does not address enhancing or controlling the exchange coupling energy.

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