Novel on-chip magnetometries using Planar Hall Resistance Sensors with high thermal stability

CIC nanoGUNE Seminars

CheolGi Kim, DGIST, Daegu, Korea
nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
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Novel on-chip magnetometries using Planar Hall Resistance Sensors  with high thermal stability **PLEASE NOTE THAT TIME HAS CHANGED; 12:00** Nanomagnetic sensors are opening a new era not only in industrial applications, especially related with information science and technology, but also in bio-medical applications, related to biochip and drug delivery. Even though the planar Hall Resistance (PHR) sensor in NiFe/IrMn and NiFe/Cu/IrMn on Si/SiO2 substrate exhibits an excellent field sensitivity, thermal stability, and linearity with +/- polarity near zero field, its characteristics are underestimated compared with the conventional AMR/GMR/TMR sensors. One of specific features of PHR sensor is thermal stability, that is, low thermal drift of sensor junction. Basically the resistance of AMR and PHR geometries is ~ 5 and 0.1 , respectively, causing that thermal noise of PHR junction is 2 order lower than AMR. Moreover, because the thermal drift in each arms are compensated in ring type junction as in Figure 1, the resistance variation with temperature, R/ T was measured to be 0.02 , of which value is ~ 100 times less than AMR junction (~15 ). Another specific feature is the tunable field sensitivity by adjusting exchange coupling field using the nonmagnetic Cu layer between NiFe and IrMn, and the ring number, from ~ a few µV/Oe for cross type to 2 mV/Oe for 7 ring sensor [1]. Thus, it has the advantage to use the PHR sensors in the robust environments, that is, on-chip magnetometries integrated in micro-fluidic channel, biochip and magnetic synapse working in harsh conditions. One of application example is on-chip channel magnetometer[2]. The measured in-plane field sensitivities of an integrated PHR sensor with NiFe/Cu/IrMn trilayer structure were h at 8.5 μV/Oe. The PHR signals were monitored during the oscillation of 35 pL droplets of magnetic nanoparticles, and reversed profiles for the positive and negative z-fields were measured, where magnitudes increased with the applied z-field strength. The measured PHR signals for 35 pL droplets of magnetic nanoparticles versus applied z-fields showed excellent agreement with magnetization curves measured by a SQUID of 3 μL volume, where a PHR voltage of 1 μV change is equivalent to 0.309 emu/cc of the volume magnetization with a magnetic moment resolution of ~10-10 emu. The minimum detectible volume of superparamagnetic drop of PHR on-chip magnetometer is 105 order lower than SQUID. Moreover, maximum magnetic moment resolution is ~ 10-14 emu in dried condition, which has 104 order better sensitivity than conventional SQUID magnetometer[3]. In this talk, I will summarize the specific features of PHR junctions and robust on-chip magnetometry applications in harsh environments. [1] B. Sinha et al, J. of Appl. Phys 113, 063903 (2013). [2] K.Kim et al, Lab Chip, 15, 696–703 (2015). [3] S. Kamara et al, Adv. Mater. 2017, 1703073 (2017). **Host** : P. Vavassori