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 alpha 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 a 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 kOmega-mum² in the AP. For the same bias voltage, the lowest alpha´s were always obtained in the parallel state (P). The lowest alpha(~ 1 E-10 mum^-2) was obtained for the lower RA sample (~500 Omegaldr mum²) saturated in P, with an applied bias voltage of 600 mV.