Development of low-noise three-axis magnetometer with tunneling-magnetoresistance sensors

Three dimensional magnetic sensors play important roles for multiple applications, e g position sensing, automotive application, and geomagnetic navigation [1]. In recent decades, many groups developed various kinds of vector magnetometer [2-8], including Hall effect [3] [6-7], the anisotro-pic magnetoresistance (AMR) effect [8], giant magnetoresistance (GMR) sensors [5], and tunneling magnetoresistance (TMR) magnetometer [2]. For all the designs, the inaccuracy in alignment of sensors or flux-guide leads to non-orthogonality between each sensing directions Another issue on three-axis magnetometer is to achieve a low-noise without increasing the size too much. In order to deal with this issues, several extrinsic methods have been reported, e g TMR arrays [9], flux concentrator [10], and flux-chopping techniques [11]. Interestingly, the 1/f noise can be reduced by a factor of 12 with a shielding type magnetic flux chopper, which was realized successfully in the ref [12]. In this work, we design and manufacture a low-noise vector magnetometer comprising three TMR sensors orthogonally aligned and placed in the central of a shielding flux chopper The non-orthogonality issue can be solved by the calibration process using a voltage-to-field transfer matrix [13].