Working principle and technology of MRAM


Ram is a storage technology that uses electron spin to store information. Nonvolatile MRAM has the potential to become a general-purpose memory, which can combine the density of storage memory with the speed of SRAM memory, and always maintain nonvolatile and high energy efficiency. MRAM memory chip can resist high radiation and can operate under extreme temperature conditions, and can be tamper proof.


The data in MRAM chip is stored by magnetic storage element. These elements are composed of two ferromagnetic plates separated by a thin insulating layer, and each ferromagnetic plate can remain magnetized. This structure is called magnetic tunnel junction (MTJ). One of the two plates is a permanent magnet set to a specific polarity during manufacturing; The magnetic susceptibility of another plate can be changed with the stored data. Renesas electronics recently added MRAM devices, which use a proprietary spin transfer torque based on vertical magnetic tunnel junction (p-mtj)MRAM  (STT-MRAM)。 The p-mtj includes a fixed and unalterable magnetic layer, a dielectric barrier layer and a changeable ferromagnetic storage layer.


In the programming operation, the magnetic field direction of the storage layer is electrically switched from the parallel state (low resistance state “0”) to the anti parallel state (high resistance state “1”) according to the current direction of the p-mtj element. These two different resistance states are used for data storage and sensing.