AMR sensor with substrate-integrated PowderMEMS® permanent magnets for in-plane biasing

Magnetic field sensors based on magneto resistive (MR) effects are fundamental components in numerous fields of application, like automotive or consumer electronics. Among them, sensors making use of the anisotropic MR effect (AMR) are in widespread use as they are inexpensive, consume low power and offer a high bandwidth from DC up to MHz. The magnetization of the ferromagnetic MR layer is commonly biased either by integration of an antiferromagnetic layer within the AMR stack or externally by means of coils or permanent magnets. Up to now, the latter approach demanded space in the sensor module and required precise discrete assembly of the external magnets. In this work, Nd-Fe-B permanent magnets are integrated in the substrate of commercial AMR devices (ADK769, Sensitec) to create customized local bias fields. The magnets are realized with the PowderMEMS® micromanufacturing technique on wafer level after processing of the AMR devices on the frontside. Magnetic measurements confirm the correct in-plane bias field strength of Hx=3.1 kA/m and thermal robustness of the magnets. The AMR devices featuring integrated magnets are assembled in a commercial current sensor design. The performance and robustness of the modified current sensor are comparable to the commercial version. The PowderMEMS® integration is scalable, avoids discrete assembly of the magnets and enables further miniaturization of the sensor module, potentially reducing packaging size and manufacturing costs. The demonstrated approach can be applied to various other microelectronic systems and MEMS whenever precise local magnetic fields are required.