Development of a very high sensitivity magnetic field sensor based on planar Hall effect

While planar Hall effect based magnetic field detection is a well-studied area, the sensing capabilities of ‘Hall cross’ sensors had not improved significantly for more than a decade. Here we report a major improvement in the sensing characteristics of ‘cross’ geometry by using pulsed laser ablation grown Permalloy as sensing material. Our sensor has two modes of operation. In the linear regime, it has a field sensitivity of 650 Ω/T with an estimated detection threshold of 5nT in open-loop condition. In switching applications, it shows a 400% output voltage swing in a range of ±0.3 mT, a value comparable with modern TMR sensors at room temperature. These values, which are the highest reported for the ‘cross’ geometry, make it applicable in a wide range of scenarios like geomagnetic field and magnetic anomaly detection. The small size of the sensing area also makes it a desirable choice for magnetic microbead based biomolecule detection.