Browsing by Author "Chang, C. R."

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Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07)
Das, Bipul
;
Lee, Y. C.
;
Li, L. C.
;
Yi-Shiou, Liu
;
Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge\'s relation, S-V (f) = AV(2)/f(alpha) (A is Hooge\'s like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Low-Frequency Noise Characterization of CoFeB/MgO/CoFeB MTJ-Based Perpendicular Field Sensor
(2016-07-01)
Das, Bipul
;
Lee, Y. C.
;
Li, L. C.
;
Yi-Shiou, Liu
;
Suen, Y. W.
We report low-frequency electrical resistance noise of Co40Fe40B20/MgO/Co20Fe60B20-based magnetic tunnel junction field sensors with reference and sensing layer magnetization directions along the out-of-plane and in-plane directions, respectively. The devices are fabricated using the sputter deposition and conventional lithography techniques with a short axis of similar to 6 mu m long and long axes of similar to 6-12 mu m long. Noise power spectra under different bias currents indicate increase in noise power with increasing bias current. A close 1/ f dependence of the noise according to Hooge's relation, S-V (f) = AV(2)/f(alpha) (A is Hooge's like constant) is observed with an average value of alpha = 1.03 +/- 0.08. In smaller devices, the magnetic field dependence of noise amplitude follows similar trend of magnetoresistance (MR) behavior without any distinct peak near antiparallel-parallel states transition of the devices, which is generally observed for magnetic defects-induced resistance fluctuation. The experimental observations infer the resistance noises in those devices that are related to the defects associated with the spin independent charge trapping at structural defects near or in the barrier layer. The device with the smallest lateral size exhibits the Lorentzian contribution, whereas the device with the largest size shows magnetic contribution in total noise. Numerically deduced magnetic fluctuations Delta B-rms of all the devices shows an average magnetic fluctuation of similar to 10 nT except for one device. The devices show the highest MR% of similar to 27% under perpendicular magnetic field with a dynamic range of similar to +/- 25 Oe and a sensitivity of similar to 0.3%/Oe. The observed low-frequency noise levels are suitable for the perpendicular field detection application and can be reduced more by improving the crystallinity of the device films stacks and their interfaces.
Magnetic tunnel junction based out-of-plane field sensor with perpendicular magnetic anisotropy in reference layer
(2015-05-07)
Lee, Y. C.
;
Chao, C. T.
;
Li, L. C.
;
Suen, Y. W.
;
Horng, Lance
A magnetic tunnel junction (MTJ) with orthogonal magnetic anisotropy and consisting of Ta X/Co40Fe40B20 1.2 (reference)/MgO 2.0/Co20Fe60B20 2.3 (sensing)/Ta 5/Ru 5 (thickness in nanometers), where X ranges from 15 to 30, is proposed and investigated in response to the demand for out-of-plane field sensors. The reference layer with perpendicular magnetic anisotropy (PMA) demonstrates tuneable coercivity ranging from 72 Oe to 175 Oe. The sensing layer exhibits in-plane anisotropy with the avoidance of exchange coupling from the PMA reference layer because of a thick MgO barrier layer. The magnetization reversal behavior of micron scale devices not only corresponds well to the sheet film, but is also independent in terms of shape and size. The magnetoresistance curve exhibits a ratio of similar to 27% in the presence of a perpendicular field and is insensitive to the in-plane field. For perpendicular field sensing, the dynamic range with a sensitivity of similar to 0.3%/Oe can achieve +/- 25 Oe with a coercive field of less than 3 Oe. Additionally, even when bias is applied up to 9.1 mV, magnetic fluctuation still stays below 0.15 mOe. (C) 2015 AIP Publishing LLC.