High-Performance Shape-Anisotropy Magnetic Tunnel Junctions down to 2.3 nm
Butsurin Jinnai, Junta Igarashi, K. Watanabe, Takuya Funatsu, H. Sato, Shunsuke Fukami, Hideo Ohno
Abstract
We show scalability down to 2.3 nm and high performance at single-digit nanometers of shape-anisotropy magnetic tunnel junctions (MTJs) employing a multilayered ferromagnetic structure. We reveal that a free layer with two ferromagnets separated by a MgO layer behaves as a single magnet at small device dimensions owing to magnetostatic coupling in addition to exchange coupling. This nature, in turn, leads to a notable performance increase of the MTJs in the single-digit-nm regime: thermal stability factor Δ of higher than 100 at room temperature; stable switching at temperatures of 150°C or higher; and spin-transfer torque (STT) switching with a dc voltage (intrinsic critical current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C0</sub> of 8.5 μA) and with a 10-ns pulse below 1.0 V. Also, we find that switching efficiency (Δ/I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C0</sub> ) increases by a factor of three or more as the size decreases. The results show that the shape-anisotropy MTJ provides a route to high-density and high-performance STT-MRAMs in the era of the ultimate scaling.