Researchers from TSMC, Sandford University, ITRI and National Yang Ming Chiao Tung University have fabricate a 64-kb SOT-MRAM based β-phase Tungsten that offers a spin–orbit torque switching of 1 ns, data retention of more than 10 years and a tunnelling magnetoresistance of 146%.
The researchers say that Tungsten is a promising heavy metal for such applications and can generate large spin–orbit torques when stabilized in its β-phase. However, the α-phase, which has a lower spin-Hall angle, is more thermodynamically stable. It is thus challenging to integrate metastable β-tungsten into complementary metal–oxide–semiconductor processes while maintaining phase stability under the back-end-of-line thermal constraints (400 °C for extended durations).
The researchers have demonstrated that the insertion of thin layers of cobalt can be used to stabilize β-tungsten under back-end-of-line-compatible thermal conditions. The composite β-tungsten layers can maintain their phase up to 400 °C for 10 h and can withstand 700 °C for 30 min. The film stacks exhibit a spin-Hall conductivity of around 4,500 Ω−1 cm−1, which was measured by means of spin-torque ferromagnetic resonance and harmonic Hall resistance measurements.
