The present disclosure relates to a storage element and a storage device incorporating the storage element. The storage element includes a storage layer which stores a magnetization state of a ferromagnetic layer as information and a fixed magnetization layer in which a magnetization direction is fixed, and changes the magnetization direction of the storage layer by the flow of an electric current.
Along with the dramatic progress of various kinds of information devices from mobile terminals to high-capacity servers, memory and logic elements configuring the information devices demand higher performance such as high integration, high speed, and low power consumption. In particular, the progress of semiconductor nonvolatile memories is remarkable and flash memories are becoming more widely used as high-capacity memory almost as if to eliminate hard disk drives from the market. Meanwhile, anticipating the progress in code storage memory or working memory, FeRAM (Ferroelectric Random Access Memory), MRAM (Magnetic Random Access Memory), PCRAM (Phase-Change Random Access Memory) and the like have been studied so as to replace NOR flash memory, DRAM and the like, which are currently used in general, therewith. Some of these memory types are already in practical use.
Among these, since MRAM records data on the basis of the magnetization direction of a magnetic material, rewriting can be performed rapidly and almost unlimitedly (1015 times or more). Therefore, the MRAM is already used in the fields of industrial automation, airplanes, and the like. Although being expected to be developed as code storage memory or working memory in the future due to the high-speed operation and the reliability thereof, actually there are problems with MRAM in realizing low power consumption and high capacity. These problems are caused by the recording principal of the MRAM in which a current is respectively made to flow through two types of address interconnects (word line and bit line) almost intersecting with each other and magnetization of a magnetic layer of a magnetic storage element, which is located at the intersection of the address interconnects, is reversed by a current electric field generated from each of the address interconnects, thereby recording information. That is, this is a fundamental problem due to the method of reversing the magnetization by the electric current magnetic field generated from the interconnects.
As a solution to this problem, a recording not using the current magnetic field, that is, a method of reversing the magnetization without using a current magnetic field has been discussed. Among these, research relating to spin torque magnetization reversal has been vigorously carried out (for example, refer to Japanese Unexamined Patent Application Publication No. 2003-17782, U.S. Pat. No. 6,256,223, Japanese Unexamined Patent Application Publication No 2008-227388, PHYs. Rev. B, 54.9353 (1996), and J. Magn. Mat., 159, L1 (1996)).
Similar to MRAM, storage elements using spin torque magnetization reversal are in many cases configured with an MTJ (Magnetic Tunnel Junction). This configuration uses a phenomenon that, when spin polarized electrons which pass through a magnetic layer fixed in a given direction enter into another free magnetic layer (where the direction is not fixed), a torque is applied to the magnetic layer (this phenomenon is also referred to as a spin transfer torque). In this case, when a current equal to or greater than a given threshold value is made to flow, the free magnetic layer is reversed. 0 and 1 are rewritten by changing the polarity of the current.
The absolute value of the current for the reversal is equal to or less than 1 mA for an element in the scale of about 0.1 μm. In addition, since this current value reduces in proportion with the element volume, scaling is possible. Furthermore, since a word line which is necessary for generating the recording current magnetic field in the MRAM is not necessary, there is also an advantageous effect in that the cell structure is simple.
Hereinafter, the MRAM using spin torque magnetization reversal is referred to as ST-MRAM (Spin Torque-Magnetic Random Access Memory). Spin torque magnetization reversal may be sometimes referred to as spin injection magnetization reversal. ST-MRAM has attracted much attention as a nonvolatile memory which can realize low power consumption and high capacity while keeping the advantageous effect of MRAM of performing rewriting rapidly and almost unlimitedly.