Piezoresistive Response of Vertical Hall Devices

This paper reports on the piezoresistive response of CMOS-based five-contact vertical Hall sensors (VHS) under mechanical stress. Single sensor elements and coupled sensor systems comprising four individual VHS were exposed to normal in-plane stress σ
_xx
along the sensor axis using a four-point bending bridge setup. The resulting stress sensitivity of the offset signals at an input voltage of
V
_in
= 3 V was below 2 μV/MPa. In addition, an inhomogeneous stress distribution was generated by applying vertical forces close to the sensor systems using an SU-8 pillar. A resulting maximum offset increase by 109 μV/N at
V
_in
= 3 V was measured. In conclusion, the influence of mechanical stress on the offset behavior of VHS is small compared to other offset sources such as the junction field effect and variations in sensor geometry.