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In this paper, recent developments in magnetic tunnel junctions (MTJs) are reported with their potential impacts on integrated circuits. MTJs consist of two metal ferromagnets separated by a thin insulator and exhibit two resistances, low (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) or high (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ap</sub> ) depending on the relative direction of ferromagnet magnetizations, parallel (P) or antiparallel (AP), respectively. Tunnel magnetoresistance (TMR) ratios, defined as (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ap</sub> $R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> )/R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> as high as 361%, have been obtained in MTJs with Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> fixed and free layers made by sputtering with an industry-standard exchange-bias structure and post deposition annealing at Ta = 400 degC. The corresponding output voltage swing DeltaV is over 500 mV, which is five times greater than that of the conventional amorphous Al-O-barrier MTJs. The highest TMR ratio obtained so far is 500% in a pseudospin-valve MTJ annealed at Ta = 475 degC, showing a high potential of the current material system. In addition to this high-output voltage swing, current-induced magnetization switching (CIMS) takes place at the critical current densities (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CO</sub> ) on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in these MgO-barrier MTJs. Furthermore, high antiferromagnetic coupling between the two CoFeB layers in a synthetic ferrimagnetic free layer has been shown to result in a high thermal-stability factor with a reduced J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CO</sub> compared to single free-layer MTJs. The high TMR ratio enabled by the MgO-barrier MTJs, together with the demonstration of CIMS at a low J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CO</sub> , allows development of not only scalable magnetoresistive random-access memory with feature sizes below 90 nm but also new memory-in-logic CMOS circuits that can overcome a number of bottlenecks in the current integrated-circuit architecture
Published in: IEEE Transactions on Electron Devices
Volume 54, Issue 5, pp. 991-1002