Chemical sensing: millimeter size resonant microcantilever performance

Abstract

Based on the use of a resonant cantilever, a mass sensitive gas sensor for the detection of volatile organic compounds (VOC) has been developed. Analyte gases are absorbed by a sensitive layer deposited on the cantilever: the resulting mass change of the system implies the cantilever resonant frequency decreases. In this paper, the process technology, based on the use of SOI wafer, is described. To integrate the measurement, piezoelectric and electromagnetic excitations are investigated and for the detection of microcantilever vibrations, piezoresistive measurement is performed. Then, the polymer choice and the spray coating system are detailed. Using various geometrical microcantilevers, the frequency dependence on mass change is measured and allows us to estimate the mass sensitivity (0.06 Hz ng−1). In gas detection the first experiments exhibit the sensor response, then by calculating the partition coefficient (K = 977), the minimum detectable concentration of ethanol is deduced and permits us to estimate the gas sensor resolution (14 ppm). Finally a comparison between millimeter size and micrometer size cantilevers shows the importance of noise in the design of an integrated sensor.

Effect of Coating Viscoelasticity on Quality Factor and Limit of Detection of Microcantilever Chemical Sensors

“…However, the oscillator configuration case differs significantly from the intrinsic noise case, in that an increase in coating thickness beyond the optimal value may seriously compromise the LOD. This phenomenon has been observed experimentally in [2] and [22].…”

“…According to (15), the sensitivity may be improved by increasing the thickness of the polymeric sensitive coating, provided that [1]. This analytical expression of the sensitivity has been verified experimentally in [7] and [22], which validate the fact that the mass effect is predominant and that the mass increase of the coating is small compared with the coating mass.…”

“…Thus, an optimum coating thickness that will maximize the SNR, hence minimizing the LOD of those devices in sensor applications, could exist. In fact, the existence of such an optimum coating thickness has been shown experimentally in coated microcantilevers [2], [22]. In Section IV, the analytical expression of the quality factor developed in this paper is used to predict such an optimum.…”

CO Gas-Induced Resonance Frequency Shift of ZnO-Functionalized Microcantilever in Humid Air

“…Our results about a decrease and an increase in resonance frequency due to gas ON and OFF are consistent with previous reports of the microcantileverbased gas detection [7][8][9][10].…”

“…In gas detection, several publications have shown that the resonance frequency of MC decreased due to exposure of the gas, such as mercury [6], volatile organic compounds [7], ethanol [8], carbon dioxide [9], freon [10], and water vapor [11]. However, for real sensor applications, the sensor response should be considered in various conditions, such as in higher humidity or vacuum conditions.…”