Electrical Low-Frequency Noise in Tunneling Magnetoresitive Heads: Phenomena and Origins

Tunneling magnetoresistive (TMR) heads have been observed to exhibit relatively large low-frequency noise. Observation in a saturating field reveals that a substantial part of this noise is of electrical origin. Two distinctly different electrical noise phenomena are observed: 1/f noise and random telegraph (RT) noise. 1/f noise appears in all heads, RT noise only in some. The magnitude of the noise tracks the device resistance and the electrical bias. Therefore, the question arises if it is caused by resistance fluctuations or by the electrical bias. To answer this question, the paper describes a measurement setup to determine the TMR device noise in thermodynamic equilibrium (no bias). It is concluded that at zero bias there is no electrical low-frequency noise; neither 1/f noise nor RT noise was detected. Further, the paper proposes an electroacoustic model for the origin of the 1/f noise and estimates the expected magnitude. For the RT noise, in addition to the well-known trapped charge blocking model, an electromigratory model is proposed to better cover all observed RT noise features