Low-frequency noise measurements on commercial magnetoresistive magnetic field sensors

Abstract

Low-frequency noise was measured in the frequency range from 0.1Hzto10kHz on a variety of commercially available magnetic sensors. The types of sensors investigated include anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR) effect devices. The 1∕f noise components of electronic and magnetic origin are identified by measuring sensor noise and sensitivity at various applied magnetic fields. Commercial magnetometers typically consist of four elements in a Wheatstone bridge configuration and are biased with either a constant voltage or current. Voltage fluctuations at the sensor output are amplified by a pair of battery powered low-noise preamplifiers and input to a spectrum analyzer. A two-channel cross-correlation technique is used when the performance of a single preamplifier is not sufficient. For the AMR and GMR sensors investigated, both electronic and magnetic components contribute to the overall sensor noise. Maximum noise occurs at the bias field which gives maximum sensitivity. The noise of TMR based sensors is primarily due to resistance fluctuations in the tunnel barrier, having little to no field dependence. The best low-field detectivity of the sensors that have been measured is on the order of 100pT∕Hz0.5 at 1Hz.

Dependence of noise in magnetic tunnel junction sensors on annealing field and temperature

“…The details of the measurement system are described in reference. 3 The total noise of the sensor can be expressed as…”

“…Magnetic and nonmagnetic noises sources contribute to the noise of a magnetoresistive based devices. [1][2][3][4][5][6][7][8][9][10] These two noise processes can be identified by comparing the noise level and sensitivity at various applied magnetic fields. At low frequencies, these noise sources are either frequency independent or frequency dependent.…”

Low-frequency noise in planar Hall effect bridge sensors

“…Comparing the detectivity of the sensors presented here to commercial AMR, GMR and TMR sensors [2] suggests that the PHEB performance is well in line, or even better than the competition. Given the opportunity of reducing the detectivity of the PHEBs even further, by increasing the dimensions of the bridges, these sensors show great promises for use in future thin-film, low-frequency magnetometers.…”

“…On the other hand, the excess 1/f noise is in general much smaller for AMR sensors and therefore it may even be that AMR based sensors exhibit better magnetic field detectivity than TMR and GMR sensors at low frequencies [2]. Planar Hall effect (PHE) sensors, which are based on the AMR effect, are presently being explored in substrate based [19] as well as for substrate free magnetic biosensors applications [20].…”

“…Magnetic field sensors based either on the intrinsic anisotropic magnetoresistance (AMR) effect of ferromagnetic materials, or the giant magnetoresistance (GMR) and tunnelling magnetoresistance (TMR) effect of ferromagnetic/non-magnetic heterostructures are today utilized in many areas of science and technology [1,2]. With reports of magnetoresistance ratios of several hundred percent at room temperature, much work is presently focused on TMR sensors with the ambition to develop a magnetic field sensor with picotesla sensitivity [3][4][5][6][7].…”