Logic gates based on spin waves
F. Ciubotaru1,*, G. Talmelli1,2, T. Devolder3, N. Träger4,
J. Gräfe4, I. Radu1, C. Adelmann1
1IMEC, 3001 Leuven, Belgium
2KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, 3001 Leuven, Belgium
3Centre de Nanosciences et de Nanotechnologies, CNRS, Université Paris-Sud and
Université Paris-Saclay, 91120 Palaiseau, France
4Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany
*E-mail: [email protected]
In conventional computational circuits, complex logic operation is performed through combinations of NAND gates. In the actual hardware, the NAND gates are implemented using transistors. While CMOS device scaling is being pushed to its ultimate limits, new paradigm-shifting technologies are required, which could completely change the way the circuits are built. The majority gate (MG) is a promising concept since it possesses a higher expressive logic power with respect to e.g. NAND or NOR gates and thus may reduce circuit complexity. Majority gates based on the interference of spin waves (SW) are promising alternatives to CMOS technology and have high potential for power and area reduction per computing throughput. The basic functionality of a such device has already been proved [1] at a mm scale using YIG films, while the device scalability to micro- and nanometer dimensions was demonstrated by micromagnetic simulations [2,3]. However, these SWMG devices are based on a “trident” shape, which leads to issues due to spin wave reflection at the bends and is difficult to implement in scaled CMOS technology due to lithography limitations.
In this work, we report on the demonstration of logic gates based on the spin wave interference in sub-micron-sized ferromagnetic waveguides using a sequential “in-line” layout of input and output antennas. The waveguides consist of CoFeB stripes of 30 nm thickness, electrically isolated from the antennas by 40 nm of SiN. The spin waves are excited by the Oersted field produced by RF currents flowing through U-shaped Au antennas (500 nm wide, 100 nm thick) and detected by the same type of transducer.
Calibrating independently the phase (0 or π) and amplitude of the spin waves generated by each input for a specific frequency/field combination, we could control the spin wave amplitude at the output, due to the wave interference. Thus, we prove the AND, OR and MG logic functions, and we show that they can operate over a rather large frequency span. Additionally, we demonstrate the inverted function of the majority gate can be obtained by the same device by tuning the operation frequency.
Furthermore, we reveal the continuous-wave operation in real time of a spin wave majority gate by time- and space-resolved x-ray magnetic circular dichroism using an X-ray microscope at Bessy II synchrotron.
This work has received funding from the European Union's Horizon 2020 research and innovation program within the FET-OPEN project CHIRON under grant agreement No. 801055.
References
[1] T. Fisher et al., Applied Physics Letters, 110, 152401 (2017)
[2] S. Klinger et al., Applied Physics Letters, APL 105, 152410 (2014)
[3] O. Zografos et al., AIP Advances, 7 (5), 056020 (2017)