Fabrication of Prototype Magnetic Coupled Spin-Torque Devices for Non-volatile Logic Applications
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Fabrication of Prototype Magnetic Coupled Spin-Torque Devices for Non-volatile Logic Applications Larkhoon Leem1, James S. Harris1, Charles Rettner2, Brian Hughes2, Xin Jiang2, See-hun Yang2 and Stuart Parkin2 1 Department of Electrical Engineering, Stanford University, Stanford, CA 94305, U.S.A. 2 IBM Almaden Research Center, San Jose, CA 95120, U.S.A. ABSTRACT A Magnetic Coupled Spin-torque Device (MCSTD) is a collective system of three interacting magnetic tunnel junctions (MTJs) that forms a novel magnetic logic gate. The fundamental principle of the MCSTD is the modification of the energy barrier for spin-torque magnetization switching of a central (output) MTJ device arising from changes in the magnetic state of two input MTJ devices. The input MTJs are placed in close proximity of a few tens of nm of the output MTJ such that their magnetic fringing fields are strong enough (> 10 Oersted) to modulate the switching characteristics of the output device. By changing the magnetic states of the two input MTJs, four possible net magnetic fields at the center MTJ can be generated. A single MCSTD thereby enables NAND, NOR and XOR operations. In this paper, the fabrication of a prototype MCSTD device is described and preliminary experiment results are reported. INTRODUCTION Despite the discovery of a number of fundamentally new spintronic phenomena and major progress in our understanding of the basic physics, we are still far from demonstrating useful logic devices, which take advantage of spintronics. For example, for field effect transistors, which utilize spin currents, there are significant challenges in spin-injection, spin transport and spin detection and, moreover, in devising schemes that could enable them to compete in performance with conventional charge based devices. For these reasons, several “non-transistor” based spintronic logic devices have been proposed [1-7]. We have presented a new spintronics device architecture using Magnetic Coupled Spin-Torque Devices (MCSTD) [8] that falls into the second category in device architecture but operates by modulating the energy barrier needed to change the state of a device as in the first category. The MCSTD logic device has power gain and fan-out, and can implement the entire Boolean logic family of devices. In this paper, we summarize the mechanism of operation of the device, discuss the fabrication of a first prototype device, and present preliminary measurement data. THEORY Device operation mechanism A Magnetic Coupled Spin-Torque Device (MCSTD) (see Fig. 1) consists of three magnetic tunnel junctions (MTJs) that interact via magnetostatic fringing fields. A central MTJ is the output of the gate and two MTJs on either side of it act as inputs. The main idea is that depending on the input MTJ magnetizations the magnetic reversal energy barrier of the output MTJ is modulated. Consequently, the current (or voltage) at which the central MTJ’s magnetic state can be switched via a spin torque transfer mechanism is altered, and thereby the MCSTD can be u
