Electrothermal analysis of molybdenum MEMS microhotplates for the optimization of temperature uniformity

In this paper it has been deepened the analysis of a MEMS (Micro Electro-Mechanical System) temperature transducer, the microheater, which uses resistance variation to determine the operative temperature. The heat up happens due to Joule effect, forcing current into the device. Generally the microheater is integrated into an insulating membrane to form the microhotplate and reduce the power consumption. The microhotplate is used in application where it is needed to reach high temperature and low power consumption as in gas sensors, infrared emitters or in the electron microscope. The sensibility of the measurement depends on the level of temperature uniformity on the surface circumscribed by the microheater, called “active area”. Normally, the central part of the microheater reaches a higher temperature than the external region. To solve the problem usually a layer of thermal conductive material is added in contact with the active area. Nevertheless, this influences directly the power consumption, costs and time to fabricate the device. In this work a new technique is realized to improve temperature uniformity. The geometry is optimized to redistribute the electrical power generated, increasing it in the peripheral area and reducing it in the central one, standardizing the temperature on the active area. Using this methodology, several geometries have been designed. First, the thermal parameters have been identified from experimental results, then using a simulator software the geometries have been designed and then fabricated. Ultimately, thought optical images and infrared thermal maps, the temperature distribution on the surface of the active area has been verified, noticing an important improvement. A paper on this work has been accepted for the conference of Eurosensor 2011. Moreover, molybdenum has been used as new material for the creation of the microheaters and its properties have been analyzed in measurements. In the thesis period at the Tudelft University of Delft, I have also collaborated on a publication for the conference Transducer 2011, which focus on the utilization of molybdenum to fabricate microheaters.