Evaluation of sensitive materials for integrated thermal flow sensors

Calorimetric flow sensors are based on a differential temperature measurement that can be performed between two sensing resistors placed at both sides of a central heating element. Typically, these elements are deposited over a thin dielectric membrane for achieving good thermal isolation. Besides the dependence of the sensor response on factors such as the chip and capsule geometry, flow regime and thermal isolation of the sensor structure, the TCR coefficient of the sensing resistors material has also a relevant influence. In this paper, we focus on the evaluation of three different sensing materials: platinum, nickel and polysilicon. Aspects like sensitivity, electrical stability and fabrication technology compatibility are analysed and their advantages and drawbacks are discussed in view of its implementation in a low cost and high yield industrial process.