Electroplated FePt Films for Micromechanical Magnetic Sensors

Herein, a ferromagnetic iron–platinum (FePt) film is deposited on a Si resonator by electroplating and patterned to form a magnetic sensor. The electroplating and annealing conditions of the FePt film are optimized to achieve micromachining with lower manufacturing costs than other deposition methods. The atomic ratio of electroplated Fe to Pt is nearly 1, which is controlled by a potential of −0.75 ± 0.02 V in a standard three-electrode electroplating system. Hydrogen annealing is performed at 750 °C, yielding an Fe-to-Pt atomic ratio of nearly 1 and achieving a coercivity of 0.3 T, which are measured using a vibrating sample magnetometer. The electroplated FePt film is patterned using the lift-off method, and the cantilever is fabricated through a standard micromachining process using a silicon-on-insulator wafer. The miniature Si resonator with the magnetized FePt film has a minimum detectable magnetic field of 20 nT. Such patterned magnets on resonators can be used for localized magnetic field detection with a magnetic moment sensitivity of ≈10⁵μ_B.