Active Compensation of Shear-Stress-Related Nonorthogonality in CMOS Vertical Hall-Based Angle Sensors

In automation, transportation, and consumer applications, countless products rely on low-cost, accurate angle sensors. A common method to realize such an angle sensor in CMOS technology utilizes two vertical Hall devices (VHDs) to measure the direction of the in-plane magnetic field components of a rotating permanent magnet through corresponding sine and cosine signals. However, the accuracy of VHD-based angle sensors was found to be compromised by, e.g., misalignment and imperfections of the fabrication processes and mechanical stress due to the piezo-Hall effect leading to nonorthogonality due to crosstalk between sine and cosine signals originating from stress-related changes of the sensitive directions. In this work, we present an active compensation method for the shear-stress-related directional sensitivity of VHD-based angle sensors. The method translates the signal of a cointegrated piezoresistive shear stress sensor into crosstalk compensation counterbalancing the direction changes and therefore re-establishing orthogonality between sine and cosine signals. The method was demonstrated with CMOS-integrated VHD and stress sensors exposed to in-plane shear stress in a torsional bridge setup at temperatures between 26° C and 96° C. As a result, at 26° C and 21-MPa stress, the standard deviation (STD) of the measured orthogonality error decreased from 2.5° to a noise-limited 0.28°, while the systematic orthogonality error was significantly reduced from 3.6° to 0.1° after compensation. This significant improvement underscores the effectiveness of the active compensation method in mitigating the impact of mechanical stress, thereby enhancing the accuracy and reliability of VHD-based angle sensors.