Impact of Contact Misalignment on Magnetic Cross Sensitivity of Integrated Vertical Hall Sensors
Monolithic integration of 3-D Hall effect sensors makes it feasible to measure all three spatial directions of magnetic fields. However, even if the integrated sensors are arranged strictly orthogonal in the semiconductor layout, measurements have shown that a magnetic field, applied perpendicular to the sensitive direction of vertical Hall effect sensors, leads to a measurable signal, resulting in an additional cross sensitivity. Typical values of this magnetic cross sensitivity vary from 0% to 10% between wafers. Thus, this effect is caused by the CMOS fabrication process. A possible reason is the tolerance of mask alignment during the semiconductor fabrication, which causes shifted contact positions of the integrated Hall element. To simulate this unwanted shift, vertical Hall elements with intentional misalignment of their contact position were designed and integrated in the same silicon substrate. A characterization of the cross sensitivity shows an enormous impact on the measured magnetic field: a shift of 1.23 mm results in a measurable cross sensitivity of 55%. Even a shift of 0.62 mm leads to 28% cross sensitivity. This makes plausible that minor tolerances in mask alignment of few hundred nanometers lead to a cross sensitivity of several percentages. For further study of this cross sensitivity, additional measurements over temperature have been performed. In contrast to the expectation that this effect may correlate to a temperature-dependent variation of the depletion region of integrated Hall elements, temperature shows no significant influence to cross sensitivity.