High density and low power design of MRAM

Advanced memory concepts for DRAM and nonvolatile memories

“…Recently MgO tunnel barriers attained as high as 260% magneto resistance [19], and multi-bit MRAM cell with 2MTJs in parallel was introduced [20]. Multi-layered MRAM as shown in Fig.…”

Consideration of optimum resistance values of MTJ in multilayered MRAM with various detection methods

“…The current in each case is represented by Eqs. (1) to (4). In this case, compared to the resistance of the MTJ, the resistance of the switching transistor was sufficiently small when on and could be ignored.…”

“…Recently, MTJ films which use MgO and have a magnetoresistance ratio (MR) exceeding 1 have been developed [3]. A method was proposed to connect two magnetic tunnel junctions (MTJ) in parallel on a single layer to produce multivalues, but the area shrinkage effect is small [4]. However, by sharing the selection transistor, serially connecting the multiple layers of the MTJ to the transistor, and making the number of information bits stored in the area of one cell multivalued, the bit unit cost can be reduced to (1/number of deposited layers) [5].…”

“…The MTJ resistance is determined by the junction area and the thickness of the tunnel insulation film. To create a resistance difference, the techniques are to vary the thickness of the tunnel insulation film or the area [4]. Here, we can approximate Ri = R 0 (1 -bV), for i = 1, 2, and consider the voltage dependence of R, where b is the voltage dependence coefficient of the resistance, and R 0 is the resistance at time V = 0.…”

Advanced memory concepts for DRAM and nonvolatile memories

“…Recently, MgO tunnel barriers have attained magnetic resistance of as high as 260% [19], and multi-bit MRAM cell with 2 MTJs in parallel was introduced [20]. Multilayered MRAM as shown in Figure 10 is a promising candidate for low-cost MRAM.…”