A study for 0.18 /spl mu/m high-density MRAM

In this paper, we study to reduce the switching dispersion and improve 0/1 separation of Magnetic Tunnel Junction (MTJ) elements in order to realize high density MRAM. Various kinds of MTJ sizes and shapes have been evaluated and conclude that in ellipse like shape pattern aspect ratio more than 2 is enough for reproducing and reliable switching characteristics. As regards the reading characteristics, the combination of the optimized MTJ pattern and process makes 21.4 sigma separation between high and low resistance states. In further study of the relation between MTJ shapes and switching distribution, we found a "Saturn" shaped MTJ has best switching behavior. Also the toggle mode MRAM is evaluated and its effectiveness for high speed programming is confirmed.