An STT-MTJ device operating below 4 K

We report the cryogenic characterization of an out-of-plane anisotropy magnetic tunnel junction with an electrical Critical Diameter of 192 nm over measured sample-stage (nominal) temperatures from 2 to 300 K using spin-transfer torque (STT) switching. Even in the low-temperature limit, the critical switching current density remains below 4 MA/cm2. After determining the magnetic properties of the film stack, we performed device-level measurements using magnetic-field and DC write-current sweeps. The tunnel magnetoresistance decreases approximately linearly with nominal temperatures, from 203% to 119%. The critical STT switching voltage remains nearly constant (<0.6 V) below 50 K and decreases monotonically at higher nominal temperatures, underscoring the suitability of STT magnetoresistive random-access memory for cryogenic memory applications. The free layer (FL) temperature during switching was estimated using finite-element simulations, which indicate that Joule heating can increase the device temperature by up to 120 K. Under the assumption of linearly extrapolated thermal conductivities, the critical switching voltage exhibits an approximately linear dependence on the FL temperature, in good agreement with the macrospin model. For a 400 ns program-erase cycle at 2 K, the mean dissipated power of the investigated device is 0.14 mW, indicating that the current density must be further reduced to enable large-scale array operation within realistic thermal budgets.