Nonvolatile MRAM and its unit structure


Because of its excellent performance, MRAM can quickly replace DRAM memory and EEPROM flash memory, which are widely used at present, as a new generation of computer memory. At present, MRAM is the best candidate for the new generation of computer memory, but it is not the only one. At the same time, fram (ferroelectric random access memory) and Oum (Ovshinsky electric unified random access memory) coexist with MRAM. Each of them has its own advantages in science and technology, and the market forecast is still difficult to predict.


Structure of MRAM device

A two-dimensional MRAM storage array is shown in Figure 1MRAMThe device is composed of orthogonal word lines and bit lines. Each MRAM cell is located at the intersection of word lines and bit lines. Through the coding of each word line and bit line, a specific MRAM unit in the device can be addressed and the data can be written or read out.


Figure 1 two dimensional MRAM cell memory array
Write state memory cell ‘0’


Structure of MRAM cell

The structure of MRAM cell is shown in Fig. 2, which is composed of four layers. The functions of each layer are described from top to bottom as follows:

The first free layer is a magnetic film for storing information, and the direction of the written magnetic field can be the same as or opposite to the direction of the arrow in the figure;

The second layer is a non-magnetic film with a thickness of only 1 ~ 2 nm, which has a tunneling barrier effect on electrons with different spin orientations;

The third pinning layer is a film with a fixed magnetic field direction in the MRAM cell,

The fourth exchange layer: antiferromagnetic film. When the MRAM memory cell exchanges information with the external circuit, the magnetic field direction of the pinning layer is kept unchanged.

In the first three layers, a non-magnetic film is sandwiched between two magnetic films. The three-layer structure is generally called spin valve or tunneling magneto resistive junction. It plays an important role in the memory function of MRAM cell, such as writing ‘0’ or ‘1’.