Effect of resistance-area product on spin-transfer switching in MgO-based magnetic tunnel junction memory cells

We use ultrafast current-induced switching measurements to study spin-transfer switching performance metrics, such as write energy per bit (EW) and switching current density (Jc), as a function of resistance-area product (RA) (hence MgO thickness) in magnetic tunnel junction cells used for magnetoresistive random access memory (MRAM). EW increases with RA, while Jc decreases with increasing RA for both switching directions. The results are discussed in terms of RA optimization for low write energy and current drive capability (hence density) of the MRAM cells. Switching times <2 ns and write energies <0.3 pJ are demonstrated for 135 nm×65 nm CoFeB/MgO/CoFeB devices.