Design and fabrication of integrated magnetic field sensing system with enhanced sensitivity

Weak magnetic field detection is always a challenging topic and sensing systems face a great challenge to be very sensitive in response to magnetic field, in the meantime, to maintain very low overall system noise. Some external auxiliary system could provide significant enhancement to overall signal-to-noise ratio (SNR) such as a magnetic flux concentrator made with soft magnetic material. In this paper, we have systematically studied and built an integrated magnetic tunnel junction (MTJ) sensing system to meet these challenges. MTJ sensor design is optimized to achieve high zero-field sensitivity of 5% MR/Oe, which is defined by the slope of the device's transfer loops at zero field, equivalent to 20 mV/Oe with 10 mA driving current. Both deposition conditions and fabrication techniques are optimized for magnetic flux concentrator (MFC) made of soft magnetic material to achieve a magnetic susceptibility of χ = 30,800 and a gain of 4 for a 100 nm thick prototype.