PSA-STT-MRAM solution for extended temperature stability

Abstract

The concept of Perpendicular Shape Anisotropy (PSA) spin transfer torque (STT) MRAM has been recently proposed as a solution to achieve downsize scalability of MRAM below sub-10 nm technology nodes, down to 3-4 nm cell size lateral dimensions. In conventional p-STT-MRAM, at sub-20 nm diameters, the perpendicular anisotropy arising from the MgO/CoFeB interface becomes too weak to ensure sufficient stability of the storage layer magnetization. In addition, this interfacial anisotropy decreases rapidly with increasing temperature, resulting in a significant drawback for applications having to operate on a wide temperature range. Here, we combine both coercivity and electron holography measurements as function of temperature to show that in a PSA storage layer, the source of anisotropy is much more robust versus temperature compared to the interfacial anisotropy of conventional STT-MRAM stacks. This allows to considerably reduce the temperature dependence of coercivity. This property is quite beneficial for applications having to operate on an extended temperature range, such as automotive (-40°C to 150°C), or to fulfill solder reflow compliance requiring 1 minute retention at 260°C.