Package stress monitor to compensate for the piezo-hall effect in CMOS Hall sensors

Package-induced stresses change the sensitivity of planar Hall plates via the piezo-Hall effect. In this paper we present a novel stress sensor which allows to compensate for this undesired mechanical cross-sensitivity. The new CMOS-compatible sensor is based on a Wheatstone bridge built of eight n- or p-doped, appropriately arranged piezoresistors. The output signal V_bridge of the sensor is proportional to σ_xx + σ_yy with the sensitivity S_bridge,σ = ∂ (V_bridge/M_bias) ∂ (σ_xx + σ_yy) = - 0.047GPa^-1. High doping concentrations larger than 10¹⁹ cm^-3 for both the n- and p-type resistors keep the relative thermal cross-sensitivity of the sensor as small as 74ppmK^-1. In contrast to conventional sensor rosettes, the new sensor has the advantage of offering a differential output signal. The measured signal was successfully used to decrease the stress-impact on sensitivity of CMOS Hall sensors by a factor of five.