MgO-based magnetic tunnel junction sensors array for non-destructive testing applications

Abstract

A MgO-based magnetic tunnel junction (MTJ) sensor including 72 MTJs in series with 50 × 50 μm2 was successfully microfabricated. Due to a two-step annealing strategy, a linear transfer curve was obtained. The tunneling magnetoresistance (TMR) value is as high as 159% and the sensitivity reaches 2.9%/Oe. The field detectivity exhibits the lowest value at 1 V bias current, attaining 1.76 nT/Hz0.5 and 170 pT/Hz0.5 for 10 Hz and 1 kHz, respectively. The results show that the sensor could be applied in non-destructive testing systems which are used for detecting small defects inside conductive materials.

Improved Magnetic Tunnel Junctions Design for the Detection of Superficial Defects by Eddy Currents Testing

“…One could therefore conclude that the best sensor configuration will be the one that produces a higher signal variation and therefore a sensor with N = 60 rows (corresponding to a height of 3 mm) would be the best solution. However, by adding rows of MTJ, the noise of the sensor will also be added with a rate of √ N compromising the SNR [12].…”

“…These sensors also show much higher sensitivities to magnetic fields when compared with AMR and GMR sensors [11], which facilitate the detection of very low-magnetic field variation that are often observed in NDT applications. Finally, it was also demonstrated that a sensor including a series of MTJ elements show improved SNRs under a homogeneous magnetic field [12]. Nevertheless, in NDT applications based on eddy currents and in particular when detecting surface defects, the magnetic field sensed by each MTJ elements of a series can be very inhomogeneous.…”

Linearization strategies for high sensitivity magnetoresistive sensors

“…CoFeB/MgO/CoFeB-MTJ data obtained at operation point. Data marked with i from references [119,123,124] and ii is unpublished data from INESC-MN; * from reference [90]; + from reference [85]; & from reference [42]; α from reference [118]; β from reference [125]; δ is unpublished data from INESC-MN; σ from reference [41]; γ from reference [83]. Comparison between single sensors (solid shapes) and sensors with integrated MFCs (half-right shapes).…”

“…Comparison between single sensors (solid shapes) and sensors with integrated MFCs (half-right shapes). Square shapes represent data for micrometric structures from reference [41], either individual circular sensors (radius of 10, 28 and 36 µm) or series of 952 square sensors (50 × 50 µm 2 each); pentagonal shape from reference [83] measured at 10 Hz; left-triangle shape from reference [125]; right triangle shape from reference [118] whereas star shape represents data for nanometric circular MTJ pillars (radius 200 nm) from reference [42]. Simple sensing layer data from reference [90] (upward triangle) and [85] (downward triangle), and SPM-like sensing layer results from reference [92].…”

Magnetic stability under magnetic cycling of MgO-based magnetic tunneling junctions with an exchange-biased synthetic antiferromagnetic pinned layer

“…[7][8][9][10][11][12][13][14][15][16][17][18][19] Applications of MTJs have extended beyond read heads in hard disk drives and MRAMs. MTJ sensors have been used for medical and biological devices, 20 high frequency oscillators, 24 non-destructive testing, 25 current sensors, 26 and ultra-low noise sensors. 27 MTJ sensors due to its high sensitivity and thermal performance have becoming an enabling technology in many areas of science and engineering.…”