Micromachined Thin Film MI Element for Integrated Magnetic Sensor

A micromachined thin film magnetoimpedance (MI) element was developed and its MI properties were investigated. Consisting of a SiN/Al/NiFe/SiO 2 film, it was formed on a Si (100) wafer and fabricated by photolithography and etching. Ni 80 Fe 20 film with nearly zero magnetostriction prepared by bias magnetron sputtering under a magnetic field was adopted as a magnetic layer in the MI element and magnetic anisotropy was induced parallel to the driving current direction. Sensitivity defined as the maximum fractional change in impedance increased with thickness and length, and was greatest for a width of 20 mum. The values for which the MI element had the best properties were 38% for the sensitivity, 1446 ppm/degC for the temperature coefficient of impedance TCZ and 712 ppm/degC for the temperature coefficient of sensitivity TCS at the driving frequency of 100 MHz. These values were much better than those of conventional magnetoresistance (MR) sensors. Therefore, these micromachined thin film MI elements have great potential for use in high sensitive integrated magnetic sensors.