Top-pinned STT-MRAM devices with high thermal stability hybrid freelayers for high densitymemory applications

New free layer (FL) materials and designs have recently drawn a lot of interest as the devices of spin-transfer -torque magnetic random access memory (STT-MRAM) keep scaling down. The so-called dual-MgO FL consisting of two CoFeB/MgO interfaces is under development. However, the perpendicular magnetic anisotropy (PMA) from two CoFeB/Mg0 interfaces is insufficient to provide the required thermal stability (A) for long data retention time for devices with critical diameter (CD) below 20nm. In our earlier work, a new FL design, the hybrid FL, was proposed. This hybrid free layer (HFL) design consists of a single layer of CoFeB coupled via a spacer to a [Co/Ni] multilayer [1]. Here, we report on the electrical and magnetic properties of the hybrid free layers in top-pinned magnetic tunnel junction (TP-MTJ) devices with various electrical CD (e -CD). We show that HFL's can provide larger coercivity (H e ) and retention (A) than dual-MgO.