Modeling of Three-Axis Hall Effect Sensor Based on CMOS Process

This work developed a three-axis Hall angle sensor suitable for the standard CMOS process, which senses the tilt angle and the absolute strength of a random external magnetic field. Several cross-shaped Hall devices were first designed and fabricated using a 0.18- $\mu \text{m}$ CMOS process, and the measurement results have been used to build scientific and reasonable foundations for modeling a three-axis Hall using COMSOL. Inside the three-axis Hall sensor, cross-shaped Hall devices detect the magnetic field in the vertical direction ( ${z}$ -axis), whereas four-Folded three-contact vertical Hall devices (4-Folded 3CVHDs) detect the magnetic field in the two horizontal directions (x- and ${y}$ -axis). The developed model has been used to investigate the important factors influencing the accuracy of the three-axis Hall angle sensor including the process misalignment and variation of the n-well thickness due to the bias current. Unlike the traditional three-axis angle sensor based on the integrated magnetic concentrator (IMC), this work can directly combine the entire sensor interface on the chip, thereby significantly reducing manufacturing costs and packaging difficulties. Besides, four complementary Hall devices are used to eliminate the offset voltage when measuring the magnetic field in a similar direction. Finally, a simulated accuracy of 0.3° and 0.22° is achieved for the angles of $\alpha $ and $\theta $ , respectively, with an external magnetic field.