Design of Circuits and Systems for Nonvolatile Nanomagnetic Logic

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Nanomagnetic logic (NML), is composed of nanomagnetic dots interacting by magnetic field coupling, and thus is a non charge-based beyond CMOS technology. It can provide exceptionally dense, robust and low power integrated systems without leakage current. The availability of nonvolatile logic states enables instant on/off capability as well as new architectures and functionalities. In our current DFG project "Field-coupled circuits in magnetic multilayers" (2009-2012), different from most other groups we have explored a technology for NML that uses nanomagnets with perpendicular, out-of-plane magnetization. This gives rise to a robust and precisely controllable switching behavior, more degrees of freedom in shape and arrangement of the magnets, and finally a denser layout. As starting point for the renewal project, we have now a processing technology, where we can set the switching threshold of single dots and the direction of signal flow in chains and logic blocks. We have experimentally verified models describing the dependencies between technology parameters, geometry and switching behavior. Further we have demonstrated the basic logic functions of inverter, fan-out and majority gate, where we use a global magnetic field as clock and as energy supply. Now it is time to look further towards more complex circuits and complete system architectures. For that purpose we want to develop a SPICE-like device model for the magnetization of single dots and the dynamics of their coupling with neighbouring dots under action of the clocking field, as well as behavioral models to be used for larger system simulation. With this, we will design clocking and synchronization schemes, including buffer circuits corresponding to CMOS flipflops. The generation of the external clocking fields and their influence on the circuit behaviour will also be investigated and optimized. In addition, we want to use our existing models and measurement data to calculate error rates resulting from non-ideal technological manufacturing processes and thermal noise, and investigate methods for robust design as well as possible error correction schemes.As a completely new approach, we propose to use vertical field coupling in the z-direction for creation of true 3D integrated circuits and systems. This offers, when using several functional layers, a very high packing density and very flexible architectures. This proposal is based upon successful pilot experiments in our own technology. With this and also with the conventional 2D arrangement, we want to design larger systems, mainly an arithmetic logic unit and FPGAs. Those profit a lot from NML due to the inherent nonvolatility and programmability during operation, and especially from the 3D integration, where an extra layer can be used for the programming function.