Noise in GMR and TMR Sensors

Abstract

Abstract. Giant Magnetoresistances (GMR) and Tunnel Magnetoresistances (TMR) take an increasing part in many applications like current sensing, magnetometry or position sensing, thanks to their high magnetoresistance at room temperature, which leads to a large output signal variation. But the real performances of such sensors can only be estimated with respect to the sources of noise. In this chapter, we give first some bases on noise theory and data treatment. Fluctuations, ergodicity and volume considerations will be discussed. A second part will detail noise measurement techniques and data analysis of typical noise power spectra. Sources of noise will be discussed in a third part. In the end of the chapter, specific cases of GMR and TMR magnetic noise and non magnetic noise will be discussed with their physical origin and their analytical or phenomenological expression. We will then present ways to design GMR and TMR sensors for noise reduction, depending on the applications targeted.

Local recording of biological magnetic fields using Giant Magneto Resistance-based micro-probes

“…GMR devices are subject to fluctuations, among which the main components are the thermal noise and the 1/f noise37. Noise spectral density measurements were performed in a magnetically shielded room.…”

Roadmap on Magnetoelectric Materials and Devices

“…The latter method is superior in terms of quantifying the sensor's intrinsic properties that are independent of experimental parameters, but is more complex, requiring a measurement of the power spectral density (PSD) of the intrinsic noise floor. The detection limit under this approach is obtained by dividing the noise √ by the sensor's sensitivity [52][53][54] (change in output signal per change in magnetic field), and the dimension of Hz -1/2 in the resulting quantity arises from the noise spectrum in this ratio. This characterization is more suitable for making comparisons across sensors that have different structures and detection mechanisms and may be tested under different parameters.…”

“…In particular, under the first method, the lowest detectable magnetic field signal can be arbitrarily improved by methods like increasing acquisition time or averaging. However, the PSD is already normalized by acquisition time [52], thus removing this source of arbitrariness.…”

High sensitivity magnetic field sensor for spatial applications

“…7. The noise level is converted into Hooge factor [7], [8], to allow direct comparison with other studies: α H (μm 2 ) = (A × f )/V 2 × S V (H), where A is the junction area (20μm 2 ), f the frequency (≈ 1 kHz), V the biased voltage (0.1 V) and S V (H) the noise under precise magnetic conditions. Fig.…”