High-speed STT MRAM incorporating antiferromagnetic layer

A previous theoretical study has shown that spin-polarized current can excite ultra-high frequency spin precessions in collinear antiferromagnetic (AF) films due to the strong antiferromagnetic coupling with the frequency spanning over a wide spectrum from giga-hertz to tera-hertz. In this paper, we present a design to incorporate the AF-based spin torque oscillator into a conventional spin transfer torque magnetic random-access memory. The AF-based oscillator consists of a perpendicular spin polarization layer and an AF layer, separated by a normal metallic interlayer. The AF layer is then exchange-coupled to the free layer on the side that is opposite to the tunnel barrier of the magnetic tunnel junction. Magnetization of the perpendicular spin polarization layer always orients in the opposite direction to that of the reference layer on the other side of the tunnel barrier. When the AF layer thickness and materials are adequately designed, the lateral spin precession in the AF layer excited by the write current provides significant assistance to the magnetization switching of the free layer, resulting in substantial reduction of the switching current threshold and the switching time.