Magnetic field measurements with a novel surface micromachined magnetic-field sensor

The surface micromachining process of Robert Bosch GmbH has been used to fa bricate a novel type of magnetic-field sensor. The Lorentz force, caused by the interaction of a current and an external magnetic field in a suspended surface micromachined conducting beam, laterally displaces the suspended s tructure. The displacement of the structure is converted into a capacitance change by comb-electrodes, which form a differential capacitor. An appropr iate electronic circuitry measures the magnetic held by quantifying the dis placement of the conducting beam. In order to increase sensitivity to magnetic fields, the magnitude of the d eflection is increased by resonant operation in a vacuum ambient, The senso r obtains its vacuum environment by encapsulation with a new wafer bonding process. Prototype sensors with resonant frequencies in the range around 1300 Hz sho w Q-factors above 30, With these samples, relative magnetic sensitivities o f 900 000 (V/A T) with a detection limit in the sub mu T-range are reported .