Geometry optimization for planar piezoresistive stress sensors based on the pseudo-Hall effect

The dependence of the sensitivity of planar piezoresistive stress sensors on geometry is systematically analyzed. The sensors in this paper are based on the shear piezoresistance effect, also termed pseudo-Hall effect. The analyzed geometry parameters are: (i) the shape of the device active area, (ii) its aspect ratio and (iii) the location and size of input and output contacts. Further, the influence of non-conducting islands in the active device area was investigated. General design rules for the design of piezoresistive stress sensors with improved sensitivity were extracted. These results were obtained using a simulation approach combining affine mapping with the finite element method. The simulation program was tested by comparing simulation results with experimental data obtained from stress sensors fabricated in CMOS technology. The differences between simulated and measured results were between 1.2 and 3.3%. Novel optimized sensor geometries with non-conducting islands show simulated and measured sensitivities greatly improved by factors up to 2.30 and 2.39, respectively. Further, the new sensors with non-conducting islands are put in perspective with classical Wheatstone bridges.