Fabrication and modeling of a silicon micro calorimeter

A prototype micro calorimeter was fabricated by IC technology processes and micromachined post-processing techniques. A rubber membrane supports two identical chambers, situated at the cold and hot junction sites of a thermopile. The thermopile consists of 666 aluminum/p⁺-polysilicon thermocouples. The power and temperature sensitivity of the sensor are 23 V/W and 130 mV/K, respectively. The response time of the sensor in air is 12 s. The chamber floors are 1 cm², while the chamber volumes are 10 to 600 μl. This high surface to volume ratio is a requirement set by the application area of surface chemistry, for which the sensor was custom designed. In order to be able to redesign the sensor to fulfil other application requirements, the prototype sensor was modeled. Two of the model parameters, the thickness of the silicon layer on the rubber support layer and the convection coefficient in air, could not be determined by means available to us. Their values were adapted until the sensitivity, as simulated with ANSYS5.3 software, and the measured value were equal. The sensitivity was further checked by analytically solving the electrical equivalent circuit of the model.