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Abstract
Magnetic sensors have been widely used in many areas that include data storage industry, health care, non-destructive evaluations, military sensing, geomagnetic and space explorations. Many of these applications require high sensitivity, low power consumption, as well as electronic circuit integration with complementary metal-oxide-semiconductor (CMOS) at room temperature.
In this dissertation, high-sensitivity magnetoresistive sensors using magnetic tunnel junctions (MTJs) are developed and studied. One aim has been to discuss design concepts for magnetic sensors and to tune critical parameters to optimize the sensor performance. The critical parameters, specifically sensitivity, linearity and noise, could be controlled by adjusting magnetic nanostructures and annealing procedures in the magnetic tunnel junctions (MTJs). The sensors were fabricated on 3-inch wafers using several pieces of cleanroom equipment. Magnetic sensors with sensitivities as high as 57,790 %/ mT have been achieved. This sensitivity is two orders of magnitude higher than those reported around the world up to date. The estimated sensitivity of our magnetoresistive sensor is 5.2 pT/Hz1/2 at 1 Hz and 170 fT/Hz1/2 at 1 kHz. We have shown that magnetoresistive sensors can achieve sensitivities in the femto-Tesla range, operating under an applied voltage of 1 V at room temperature and dissipating only 25 μW of power.
