In recent years, a semiconductor memory with a resistance change element such as a PRAM (phase-change random access memory) or an MRAM (magnetic random access memory), has been attracting attention and being developed, in which the resistance change element is utilized as a memory element. The MRAM is a device which performs a memory operation by storing “1” or “0” information in a memory cell by using a magnetoresistive effect, and has such features as nonvolatility, high-speed operation, high integration and high reliability.
A large number of MRAMs, which use elements exhibiting a tunneling magnetoresistive (TMR) effect, among other magnetoresistive effects, have been reported. One of magnetoresistive effect elements is a magnetic tunnel junction (MTJ) element including a three-layer multilayer structure of a recording layer having a variable magnetization direction, an insulation film as a tunnel barrier, and a reference layer which maintains a predetermined magnetization direction.
The resistance of the MTJ element varies depending on the magnetization directions of the recording layer and reference layer. When these magnetization directions are parallel, the resistance takes a minimum value, and when the magnetization directions are antiparallel, the resistance takes a maximum value, and information is stored by associating the parallel state and antiparallel state with binary information “0” and binary information “1”, respectively.
Write of information to the MTJ element involves a magnetic-field write scheme in which only the magnetization direction in the recording layer is inverted by a current magnetic field resulting from a current flowing through a write wire and a write (spin injection write) scheme using spin angular momentum movement in which the magnetization direction in the recording layer is inverted by passing a spin polarization current through the MTJ element itself.
In the former scheme, when the element size is reduced, the coercivity of a magnetic body constituting the recording layer increases and the write current tends to increase, and thus it is difficult to achieve both the miniaturization and reduction in electric current.
On the other hand, in the latter scheme (spin injection write scheme), as the volume of the magnetic layer constituting the recording layer becomes smaller, the number of spin-polarized electrons to be injected, may be smaller, and thus it is expected that both the miniaturization and reduction in electric current can be easily achieved.
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