Characterisation and modelling of the mismatch of TCRs and their effects on the drift of the offset voltage of piezoresistive pressure sensors

Based on the assumption that each piezoresistor of a silicon pressure senso r has its own temperature coefficients (TCRs of the first and second order) , a theoretical model has been developed in order to study the thermal beha viour of the offset voltage. We first derive the expression for the drift o f the output voltage of each potentiometric circuit obtained from the whole bridge, and then that for the thermal variations of the offset voltage its elf. It is shown that the existence of a small difference between the tempe rature coefficients of the four piezoresistors can provoke thermal variatio ns of the output voltages whose shapes can obey to a linear or a parabolic law. On the other hand, we have used an experimental procedure, on our test pres sure sensors, allowing us to extract the piezoresistors TCRs, to measure th e thermal drifts of the output voltage of each half-bridge, and those of th e whole bridge. The application of the theoretical model shows that there e xists a good accordance with the experimental results. The parabolic shapes of the outputs of the two half-bridges, and also that of the offset voltag e, are explained by the mismatch of the TCRs of the four piezoresistors. (C ) 2000 Elsevier Science S.A. All rights reserved.