PicoTesla magnetic tunneling junction sensors integrated with double staged magnetic flux concentrators

Abstract

Ultra-sensitive solid-state magnetic sensors are in strong demand in many applications where currently available sensors are inadequate. We have used high performance magnetic tunneling junction (MTJ) sensors and pushed the magnetic sensing limit to a high level. We have incorporated double-staged magnetic flux concentrators, one on the MTJ chip level and the other on a more macroscopic level, to amplify the external field of interest. With this approach and undergoing a process of optimization on the flux concentrators, we have increased the sensitivity of the MTJ sensor by a large factor of 517 to 775.4%/Oe in terms of magnetoresistance response. The coercivity of the sensor is only 0.12 Oe. We have achieved a detectable field limit of 30 pT/Hz at 10 kHz. We have presented the noise spectrum and the sensitivity spectrum up to a maximum frequency of 100 kHz.

Micron-Scale Anomalous Hall Sensors Based on FexPt1−x Thin Films with a Large Hall Angle and near the Spin-Reorientation Transition

“…Instead of extracting the field sensitivity from a Hall curve, we measured the sensitivity using an AC method, as described previously in detail [ 2 , 5 ]. This method provides an accurate measurement of the sensitivity, while the sensitivity derived from the slope of the Hall curve may be overestimated [ 37 , 38 , 39 ]. Noise measurements using a two-channel cross correlation method [ 40 ] have also been described in detail in our previous works [ 2 , 5 , 11 ].…”

Double-Gap Magnetic Flux Concentrator Design for High-Sensitivity Magnetic Tunnel Junction Sensors

“…However, this type of sensor requires cryogenic refrigeration to operate, and the sensitivity is proportional to the superconducting flux area [10,11]. Magnetic flux concentrators (MFC) are another competitive method to improve the properties of MTJ sensors [12,13,14,15,16]. Firstly, it is easy to realize industrial production with low cost and low power consumption by using the mature integrated circuit technology, which benefits the miniaturization of the sensor system.…”

Magnetotransport and electronic noise in superparamagnetic magnetic tunnel junctions

“…For sensitive magnetic field sensors with a small size and massproduction potential, a magnetic tunnel junction (MTJ) sensor is a promising candidate, which has been shown to have picotesla detectability at room temperature. [1][2][3][4][5][6] To reach better sensing detectability, it is essential to study the intrinsic noise of MTJs. The intrinsic noise may also give more information on defects and magnetic dynamics of MTJs than simple transport measurements.…”

“…More details of MTJ fabrication can be found in our previous work. 6,20 The magnetotransport properties at room temperature are measured on a probe station equipped with a pair of calibrated electromagnets. For the temperature dependence study, a Quantum Design V R Physical Property Measurement System (PPMS) is used to set temperature from 150 K to 400 K, as well as the external magnetic field from À7 T to 7 T. A block diagram of the noise measurement system is shown in Fig.…”

“…It should be noted that the sensitivity based on this calculation may be overestimated due to the finite coercivity, as found in previous work. 5,6,19,25 At T < 350 K, sensitivity shows a strong dependence on the bias field, yet only changes slightly with respect to temperature. At T > 350 K, sensitivity of MTJ drops rapidly, as magnetic susceptibility of superparamagnetic nanoclusters declines at higher temperatures.…”