Low-Frequency Noise in MgO Magnetic Tunnel Junctions: Hooge's Parameter Dependence on Bias Voltage

Low-frequency noise was studied in MgO magnetic tunnel junctions (MTJs). The junctions were analyzed under saturating magnetic fields to minimize the noise of magnetic origin. Low-frequency noise of magnetically saturated MTJs is dominated by two different types of electrical noise: 1/f noise and random telegraph noise (RTN). 1/f noise is always present and represents the ultimate limitation for low-frequency applications. The RT noise component has a higher contribution for lower resistance area (RA) product samples and its magnitude increases with bias voltage. The 1/f noise of different MTJs can be compared using the Hooge parameter (alpha). This paper shows a systematic decrease in a with increasing bias voltage for MTJs with varying RA. All the MTJs studied, for both memory and sensor applications with single and double barrier, exhibit higher alpha variations while saturated in the anti-parallel state (AP) and no significative dependence on bias polarity was observed. Variations above one order of magnitude were observed for MTJs with RA > 10 k Omega center dot mu m(2) in the AP. For the same bias voltage, the lowest a's were always obtained in the parallel state (P). The lowest alpha(similar to 1 E-10 mu m(2)) was obtained for the lower RA sample (similar to 500 Omega center dot mu m(2)) saturated in P, with an applied bias voltage of 600 mV.