From Three-Contact Vertical Hall Elements to Symmetrized Vertical Hall Sensors with Low Offset

This paper gives a detailed account of vertical Hall sensors (VHS) with an electrical symmetry equivalent to that of planar Hall plates (PHP). Conventional five-contact VHS (5CVHS) have shown strongly nonlinear offset characteristics due to the junction field effect combined with an inherent electrical asymmetry which have prevented efficient offset compensation by current spinning. We show that this deficit can be cured by appropriate device design. The novel sensor achieves a higher symmetry by four identical three-contact vertical Hall elements (3CVHE) interconnected into what we call the fully symmetric VHS (FSVHS). In this device offset compensation by current spinning is found to be at least ten times more efficient than in comparable 5CVHS. Quantitatively, at a drive current of 0.5 mA the residual magnetic offset field of the FSVHS extracted from 50 samples is 0.14 ± 0.41 mT. In 5CVHS devices the corresponding value was found to be 2.04 ± 1.32 mT. Moreover, by orthogonal coupling of four FSVHS the device is symmetrized even further, which results in an equivalent magnetic offset field of 0.04 ± 0.05 mT. This represents the best results to date achieved by a stand-alone VHS in standard CMOS technology. For comparison the magnetic offset of conventional PHP fabricated in CMOS technology lies in the range of 0.05 to 0.1 mT, between the results of the two novel concepts.