The Effect of CoFeB Electrodes Compositions on Bias Voltage Dependence of Sensitivity in Tunneling Magnetoresistance Sensors

Sensitivity is one of the key characteristics of tunneling magneto resistance sensors. It has been shown that bias voltage has a strong impact on the sensitivity, which typically increases at low bias, peaks at a certain bias, and then reduces at higher bias. However, no studies on the effect of CoFeB active layer on sensitivity have been conducted. We investigated the sensitivity dependence on bias voltage magnitude and polarity in sensors with CO20Fe60B20, CO40Fe40B20 and CO60Fe20B20 active layers. In contrast to the CO40Fe40B20 and CO20Fe60B20 sensors, the CO60Fe20B20 sensors did not exhibit a voltage-controlled magnetic anisotropy effect. The sensitivity of CO40Fe40B20 and CO20Fe60B20 sensors increased rapidly and without saturation under positive bias, reaching up to ten times that of negative bias. The bias dependence of the derivative induced by the voltage controlled perpendicular anisotropy modification is responsible for the high increase and asymmetry in sensitivity. The high increase and asymmetry caused by the anisotropy modification are stronger in sensors with weaker perpendicular anisotropy and CO20Fe60B20 electrodes. The results indicate that a higher Fe content in CoFeB alloys enhances the voltage controlled perpendicular anisotropy modification, allowing for a stronger increase in sensitivity by the bias.