MAGNETIC SENSORS FOR NANOTESLA DETECTION USING PLANAR HALL-EFFECT

We have fabricated sensitive magnetic sensors based on the planar Hall effect with a field resolution below 10 nT. The sensor response is li near over at least four decades. Due to the transverse measurement con figuration, the noise associated with thermal drift at 1 Hz is reduced by four orders of magnitude compared to a similar longitudinal magnet oresistive sensor. The active material consists of permalloy ultrathin films (60 Angstrom thick) on top of a Fe/Pd bilayer epitaxially grown on MgO (001) by molecular beam epitaxy. A process-induced uniaxial ma gnetic anisotropy is built into the Fe/Pd bilayer, which then ensures that the magnetization at zero field is aligned with the current regar dless of the magnetic history of the device. Optimized devices exhibit a sensitivity of 100 V T-1 A(-1). In order to shift the range of oper ation towards lower fields, it is shown that a process-induced uniaxia l anisotropy can be built into FeNi layers grown on Si(100) substrates . Planar Hall-effect sensors fabricated with such material exhibit sen sitivities up to 300 V T-1 A(-1).