Magnetic tunneling applied to memory (invited)

Random access magnetoresistive memories have been designed using anisotropic magnetoresistive ~AMR! material and more recently giant magnetoresistive ~GMR! material. The thin films in these memories have low sheet resistivities ~about 10 V/sq!, resulting in cell resistances of 10 to 100 V at competitive areal densities. High sense currents of a mA or more are required to get signals on the order of a few mV. Spin dependent tunneling ~SDT! devices are intrinsically high impedance, with typical equivalent resistance values of 10– 10 V for a square micron area. SDT cells have the potential for signals on the order of 10 mV with lower sense currents, and hence, faster access times than GMR memory. A GMR pseudospin valve memory concept is presented for comparison with SDT memory. Three different design approaches are discussed for SDT memory: ~1! high-density memory arrays similar to those in AMR and GMR memories, ~2! a transistor per cell approach similar to semiconductor dynamic random access memory, and ~3! embedded SDT devices in a flip–flop cell similar to semiconductor static random access memory. The conclusions are: ~1! SDT memory is potentially higher speed than GMR memory, ~2! SDT memory has no area advantage compared with dense GMR memory, and ~3! risks with SDT memory include ~a! processing ultrathin dielectric layers uniformly and reliably that are compatible with integrated circuits and ~b! attaining sufficiently low impedance levels to get a satisfactory signal-to-noise ratio in a small area cell. © 1997 American Institute of Physics. @S0021-8979~97!56908-8#