*7.2.3 MRAM: spintronic synaptic devices*

Magneto-Resistive Random Access Memory (MRAM) is a kind of non-volatile memory (NVM) that can retain saved data even if the power is out or is unintentionally turned off. MRAM, commonly known as Magnetic RAM, is not brand-new. MRAM has been available on the market for more than 20 years, but recent advancements in the technology have allowed it to be employed successfully in both new and old applications.

Magnetic Tunnel Junction (MTJ), a part of MRAM technology, is a combination of two ferromagnetic layers and an insulating layer. MRAM stores a logic 1 or a logic 0 by altering the resistance of an MTJ. Two ferromagnetic layers' relative spin orientations determine the resistance of the MTJ, which has two resistance options: high resistance and low resistance.

According to **Figure 10**. The free layer of the MTJ can have its magnetic direction modified by applying polarised currents or magnetic fields, whereas the reference layer of the MTJ maintains a constant magnetic direction. The resistance of the MTJ is minimal when the directions of the reference layer and the free layer coincide (a logic 0 is stored). However, resistance is strong if they are going in opposite directions (a logic 1 is stored).

Toggle mode technology, in which a magnetic field modifies the electron spin to program/write bits, was utilised by the initial generation of MRAM devices. Although it was simpler to build toggle MRAM, scaling it down is challenging. As the write lines get smaller and other difficulties arise, the current needed to flip the bit does not decrease in value. Following generations of MRAM devices began utilising a different technique known as Spin-Transfer Torque (STT) MRAM. SST MRAM uses a spinpolarised current to change the spin of electrons, making device scaling down simpler and less expensive. However, the majority of STT MRAM devices now available use a perpendicular strategy in which electrons spin horizontally and change perpendicular to the plane (**Figure 11**). This perpendicular method provides the benefit of offering higher density memory products by permitting lower switching currents with fewer transistors and less power consumption.

*Neuromorphic Computing between Reality and Future Needs DOI: http://dx.doi.org/10.5772/intechopen.110097*

#### **Figure 10.**

*Structure of a MTJ. (a) Anti-parallel (high resistance) and (b) parallel (low resistance) [250].*

#### **Figure 11.** *Perpendicular MTJ diagram [251].*

STT-MRAM products now on the market have the benefit of being faster and using less power than NVM flash memory devices. They could also compete with volatile memory units like SRAM and DRAM due to their potential speed as well as their ability to be scaled down even smaller than 10 nm. They are even more appealing to embedded memory applications because of this property. STT-MRAM has inherent limitations, much like many other technologies, and only time will tell if this technology will take the place of DRAM or SRAM. STT-MRAM technology offers intriguing applications in neuromorphic computing, automotive microcontrollers, and systemon-chips (SoCs).
