1. Field of the Invention
The present general inventive concept disclosed herein relates to a semiconductor device and a method of fabricating the same, and more particularly, to a magnetic memory device and a method of fabricating the same.
2. Description of the Related Art
Typical semiconductor electronic devices use electrical characteristics depending on the charge quantities, whereas spintronic devices use the electrical characteristics depending on the spins of electrons. Examples of the spintronic devices are magnetic memory devices that use the spin of electrons to store data and read the stored data. The magnetic memory devices can be classified into a giant magneto-resistance (GMR) element using a GMR effect and a tunneling magneto-resistance (TMR) element using a TMR effect.
The GMR effect, which was first discovered in an Fe/Cr artificial lattice by M. N Baibich et al. in 1998, is generally a magneto-resistance effect that occurs when a ferromagnetic layer and a nonmagnetic layer form an artificial lattice. It is known that a relatively large magneto-resistance (MR) can be achieved even under the condition of a weak magnetic field when an anti-ferromagnetic layer/a ferromagnetic layer/a nonmagnetic layer/a ferromagnetic layer such as IrMn/NiFe/Cu/NiFe are sequentially stacked. However, since there is exchange coupling between thin layers in an artificial lattice structure, the GMR element using the artificial lattice structure is lower in MR than the TMR element.
The TMR effect is a magneto-resistance effect that occurs when a pair of ferromagnetic layers have a thin tunnel insulating layer interposed therebetween. The TMR effect was already discovered in the 1970s, but a TMR element based on the TMR effect started to attract public attention after it was proved in 1995 by Moodera et al. that the TMR element can achieve a large MR of 18%. In particular, since the TMR element has little exchange coupling between ferromagnetic layers, it can achieve a large MR even under the condition of a weak magnetic field. For example, it was proved that a magnetic tunnel junction (MTJ) device using an aluminum oxide layer or a magnesium oxide layer as a tunnel insulating layer can achieve a large MR of about 70% to about 200%.
FIG. 1 is a graph illustrating the characteristics of a GMR element and a TMR element.
Referring to FIG. 1, the TMR element is much larger in MR than the GMR element. Also, the TMR element is much smaller than the GMR element in terms of a switching current for data storage. In this respect, the TMR element can provide the characteristics of a large MR and a small switching current required for magnetic memories.
However, a further-reduced switching current is required in order to further increase the integration level of magnetic memories. In the case of the TMR element, the switching current can be reduced by increasing the thickness of the tunnel insulating layer, but an increase in the tunnel insulating layer's thickness leads to a decrease in the MR. On the other hand, a decrease in the tunnel insulating layer's thickness may lead to not only an increase in the write current but also a decrease in the reliability and endurance of the product.