Search

This work discusses the design, finite element method modeling (FEM), fabrication and characterization of a silicon-based, catalytic micro calorimetric sensor. The sensing area is comprised of two titanium silicide (TiSi 2 ) – polysilicon (poly-Si) resistive temperature sensors symmetrically positioned relative to a poly-Si heater on which an oxidation promoting catalyst is deposited. The resistive structures are located on a suspended, thereby, thermally isolating, low mechanical stress membrane and integrated into a glass flow channel. The micro-calorimetric sensor is applied for measuring propane and hydrogen concentrations in air. An approach to optimization of thermal and fluidic design of the microsensor is presented based on developed models: (i) a 3D thermo-electric analysis of the suspended heater and (ii) a 2D thermo-chemical analysis of the catalytic oxidation of propane in the flow channel. Influence of the design and material of the membrane on the power consumption and temperature distribution across the sensing area are analyzed. A relationship between the thermal design of the sensor, reaction conditions and its operation as a thermal actuator and sensor of reaction heats are discussed. Various thermo-electrical characterizations (electrical, infrared surface imaging and transient thermal response measurements) in the context of microcalorimetric sensing are performed. Microsensors with a 50 μm × 50 μm sensing area consume ca. 12 mW at an operational temperature of 350 °C. Thermal imaging with an infrared camera indicates local heating with a temperature gradient across the active area estimated to be 4 °C μm −1 (at ca. 500 °C). The heating and cooling times are found to be ca. 1 and 8 ms, respectively. Temperature vs. power curves are determined for both stationary and constant flow conditions of various gases. Based on the experimental and modeling results we envision that these microsensors can be successfully used for calorimetric sensing and analysis of gaseous samples. [ABSTRACT FROM AUTHOR]

Abstract: In this work we present a low-cost, low-power, small sample volume microcalorimetric sensor for the measurement of reaction heats. The polysilicon-based microcalorimetric sensor combines several advantages: (i) complementary metal oxide semiconductor technology (CMOS) for future integration; (ii) elements of silicon micromachining (MEMS) to control thermal performance; (iii) heterogeneous catalysts for selective detection and analysis of individual gas compounds; and (iv) microfluidics for optimized control over the reaction conditions. A comprehensive study on the electrical properties of polysilicon thin films as a potential material for temperature monitoring of highly exothermic reactions is presented. Resistive measurements were performed up to 800°C and a temperature coefficient of resistance (TCR) of 3.24×10−4/°C was derived in the quasi-linear resistive range between 300 and 500°C. The polysilicon thin film temperature sensors show a good stability. Due to its excellent compatibility with silicon technology and chemical inertness, doped polysilicon thin films can be successfully applied in catalytic microreactors and sensor microsystems at high operating temperatures. We demonstrate the performance of polysilicon sensors by the detection of reaction heats for a model reaction – the catalytic oxidation of propane in air at concentrations in the range of 0.01–0.8vol.% which is below the low explosion level (LEL) of propane of 2.1% . The sensor exhibits immediate and reversible response upon exposure to propane in air. By choosing a selective catalyst the specificity of the sensor can be tuned to different gases. [Copyright &y& Elsevier]