1. Field of the Invention
The present invention relates to a memory device using a multi-domain states of a ferromagnetic material, and more particularly to a magnetic memory device, in which a ferromagnetic layer for recording magnetic data serves as a sensing layer so as to have a simple structure, shorten a manufacturing process, and reduce the unit cost of production. The planar hall effect or magneto-resistance is used to measure multi-domain states so as to read data stored in a multi-level state.
The present invention relates generally to a memory device designed for memory or data storage. It also is related generally to electronic device which uses single or multi-domain states of ferromagnetic material for data storage. Particularly, this magnetic memory device is composed of thin ferromagnetic film which acts as recording layer as well as sensing layer, resulting in simple structure, shortened manufacturing process, and reduced cost of production. This device reads information data by measuring planar Hall effect or magneto-resistance on multi-domain states of ferromagnetic film and writes information data by external magnetic field generated by extra metal wires.
2. Description of the Related Art
Generally, magnetic memory devices have been recognized as memory devices, which can be substituted for dynamic-RAMs (DRAMs), static-RAMs (SRAMs), flash memories, etc., and will be widely used in mobile instruments, such as smart cards, mobile terminals, and portable telephones, as well as computers.
DRAMs, which are most widely used now, are volatile memories that lose all stored data when the power is shut off, and thus require a long time to operate the DRAMs back to in an initial state. In order to solve the above drawback, Fe (ferroelectric) RAMs are proposed. The Fe RAMs are in a commercially usable state, but require a high voltage in an initial state and have a complicated structure. Magnetic-RAMs (MRAMs) solve the above disadvantages. It has high operation speed at low voltage, and thus are prosperously researched now.
FIG. 1 is a schematic view of a conventional MRAM device.
With reference to FIG. 1, the conventional MRAM device uses a giant magneto-resistance (GMR) effect such that resistance is highly varied when two top and bottom magnetic layers interposed by a non-magnetic layer have different spin directions in comparison with the same spin directions. The device has a complex structure with the multiple magnetic layers based on a spin valve structure.
The conventional MRAM device includes a hard magnetic layer formed under a space layer and serving to perform a sensing function, and a soft magnetic layer formed on the space layer and serving to perform a storing function.
Here, the magnetization direction of the soft magnetic layer is written by applying current along word lines and a variation of resistance due to the magnetization directions of the two magnetic layers is sensed. Thus, the information bits according to the magnetization directions of two layers are written.
However, the conventional MRAM device has a complicated structure due to the multiple magnetic layers forming spin valves and layers firming word lines and read lines, thus having problems, such as a difficulty in a manufacturing process and deterioration in productivity.
Further, since data stored in one cell are 1 bit data representing “0” and “1”, the conventional MRAM device stores a small amount of data in spite of the complicated structure.