The continuous spinning current (CSC) stress sensor method for the extraction of two stress components in an offset compensated manner

This paper reports on a novel method to extract two independent stress components from a single sensor with four peripheral contacts. The stress dependent signals are temperature compensated to first order and separated from other undesired signal contributions using the Fourier transform. To date, such results have been obtained only using two separate four-contact structures, e.g., Wheatstone bridges of piezoresistors and piezo-FETs, or using structures with a larger number of contacts. Similar to the continuous spinning current (CSC) method for Hall devices, the method applies a continuously spinning current to a silicon n- or p-well device. It permits to (i) extract both σxx − σyy and σxy stresses; (ii) separate the stress dependent signals from other undesired signals, such as Hall voltages, thermoelectric voltages, and temperature dependent effects; and (iii) to integrate four-contact stress sensors into mixed signal systems without further means to compensate the offsets due to the amplifier and A/D conversion stages. Further, the approach is also applicable to nonlinear devices. The method has been verified with two separate four-contact sensors rotated by 45°.