Comparative performance of static-mode ferrous MEMS gradiometers fabricated by a three-step DRIE process

Two MEMS structures—a cantilever beam and a quad-beam—have been designed and fabricated through a three-step deep reactive ion etching (DRIE) process. Devices feature target patterns to align with an external optical detection system and a micromachined cavity to embed an NdFeB hard mini-magnet, thus releasing the stress of structures. Structures are intended for magnetostatic gradient measurements. Induced magnetic fields generate an attracting force on the magnet that deflects the sensor. Deflection is optically detected through nanometer-resolution confocal microscopy. The static-mode sensitivity of up to 1.86 × 10−4 T m−1 demonstrates that MEMS gradiometers are able to perform in situ gradiometry with a single sensor and miniaturized size. Suitable techniques for integrated detection are discussed.