Magnetic Conductive Filament Formed in the Reram Device with Ferromagnetic Electrode

Abstract

We have studied electrical transport properties of the ReRAM device with ferromagnetic electrode, in order to understand origin of the nano-conductive filament (NCF) which was formed in the low resistance state (LRS). We observed anisotropic magnetoresistance (AMR) in the device having ferromagnetic electrode at one or both sides of electrodes. [1, 2] The device structure is Ni(40 nm)/HfO2(3.8 nm)/FeNi(40 nm). The size of the cross-point device area is 1×1 μm2. The HfO2 layer was deposited by reactive sputtering using Ar and O2mixture gases. Figure 1 shows the resistance switching characteristics of the ReRAM device with two ferromagnetic electrodes. The bipolar operation was observed. We measured magnetic conduction property of the LRS, as shown in Figure 2. Direction of the magnetic field is in-plane and parallel to the Ni top electrode. The structures of the devices in Figure 2-a and 2-b are same, but the shapes of magnetoresistance were quite different. Negative magnetoresistance appeared in the sample #1 (Fig.2-a), however, positive magnetoresistance appeared in the sample #2 (Fig.2-b). Both cases showed hysteresis property against change in the magnetic field, and there are abrupt changes in MR ratio around 200 mT. These magnetoresistance properties are considered to be anisotropic magnetoresistance. Positive MR appears when magnetic field is parallel to current, and negative MR appears when the magnetic field is perpendicular to the current. It is suggested that NCF is parallel to the field for #2, and perpendicular to the field for #1. In our samples, dielectric layer of HfO2surrounds the bottom Ni electrode, and NCF formation occur either at the top or at the sidewall of the bottom electrode. The abrupt MR jump may be related to single domain switching in the narrow magnetic NCF, and detailed discussion based on micro-magnetic simulation is in progress.