A CMOS-compatible 2-D vertical Hall magnetic-field sensor using active carrier confinement and post-process micromachining

Abstract

This work presents a CMOS-based magnetic-field sensor for the detection of magnetic-field vector components that occur parallel to the chip surface. The device employs two vertical Hall plate structures embedded in the substrate orthogonal to each other. The sensor is fabricated using a standard 3 μm CMOS process provided by a commercial integrated circuit (IC) manufacturer, and a maskless post-process bulk-micromachining step. The sensor makes use of standard p+ implants to bound the plate region for the purposes of: (a) actively confining majority carriers to a narrow channel, thereby enhancing sensitivity; and (b) acting as an etch-stop layer. The micromachined cavities act to reduce detrimental cross-sensitivity effects. Sensitivity is found to vary with negatively increasing p+ confinement voltage, but appears to saturate due to a pinch-off effect.