Micromachined thermal inclinometer based on flash evaporated Bi0.5Sb1.5Te3(p)/ Bi2Se0.3Te2.7(n) thermocouples
Résumé
The techniques of micromachining are used for the manufacturing of a thermal inclinometer, which requires no solid proof mass and has a low-cost production. The sensor principle is as follows: a heating resistor creates a symmetrical temperature profile and two thermocouples, placed symmetrically on both sides of the heater, measure a differential temperature. When an acceleration is applied on the sensitive axis x of the sensor, the convection heat transfer and the temperature profile become asymmetric and the differential temperature was shown to be proportional to the acceleration and to the Grashof number. Platinum resistor deposited by electron beam evaporation and flash evaporated Bi0.5Sb1.5Te3(p)/Bi2Se0.3Te2.7(n) thermocouples are used, respectively, as heater and temperature sensors on a polyimide substrate. These ternary materials present higher figures of merit than 10-3 K-1 and the thermocouple sensitivity is 440μV K-1. Two types of sensors have been manufactured: the first one is deposited on a continuous polyimide film and the second one on a micromachined film, which permits to limit the energy consumption by a factor of 2 and to obtain a heater temperature rise of 3.44KmW-1 and a sensitivity of 1410 μV g-1 (1g = 9.81 m s-2) for a heating power of 100 mW.