Magnetoresistive Random Access Memory (MRAM) is a non-volatile memory technology that has read and write response times comparable to volatile memory. MRAM typically uses a magnetic memory cell or device to store information by changing electrical resistance of a magnetic tunnel junction (MTJ) element. The resistance state changes corresponding to that of the magnetic orientation of a free layer relating to a fixed magnetic layer of the MTJ element, which may be in either a parallel (P) state or an anti-parallel (AP) state.
The write operation in MRAM cell requires a bidirectional current to achieve switching between the P and AP resistive states. The current required to switch the magnetization direction of the MTJ element between the resistive states (e.g., P to AP, or AP to P) may be different. Generally, the access transistor coupled to the MTJ element becomes source-degenerated during one of the state transitions. This may lead to a significant reduction in drive strength and adversely affect the operation of the MTJ element. During the other state transition, when the access transistor is not source-degenerated, excessive current may flow through the MRAM cell, resulting in unnecessary power consumption. This may degrade MTJ reliability due to a higher voltage drop across MTJ. Consequently, conventional MRAM cells require high write power and have poor write-ability.
From the foregoing discussion, it is desirable to provide low power magnetic memory cells with improved reliability and writing performance in memory applications.