Transient Signal Analysis Using Complementary Metal Oxide Semiconductor Capacitive Chemical Microsensors

Abstract

This work explores the possibility to discriminate analytes based on their nonequilibrium signals in polymer-coated capacitive chemical microsensors. The analyte uptake in the chemically sensitive polymer layers of 3-7-microm thickness has been analyzed using a diffusion model and the dynamic sensor response data. The shapes of the response profiles have been calculated analytically. Despite the simplifications in the model, the observed transient signal profiles could be described accurately. Comparison of the measured diffusion coefficients (on the order of 10(-12) m2/s) with literature values measured at similar concentration levels showed good agreement. Concentration-independent diffusion coefficients for several analyte/polymer combinations (poly(etherurethane)/all analytes; poly(epichlorohydrin)/alcohols) as well as slightly concentration-dependent diffusion coefficients (poly(epichlorohydrin)/toluene or ethyl cellulose/toluene) have been found in the investigated concentration range of tens to hundreds of pascals gas-phase partial pressure. The diffusion times of water and the first aliphatic monohydric alcohols in the polymers are strongly correlated to their molecular size. The discrimination of these substances based on dynamic sensor data of a single sensor could be demonstrated. In particular, the analysis of mixtures of analytes with similar chemical behavior (water/ethanol or methanol/ethanol) by means of analyzing the response profile of single-exposure steps or by applying a series of decreasingly long alternating target gas exposure and carrier gas exposure steps has been performed.

Inkjet and microcontact printing of functional materials on foil for the fabrication of pixel-like capacitive vapor microsensors

“…It presented a hysteresis that although it was larger for the staircases than for the steps, it was very small in any case, reaching a maximum value of only 0.266% (or $4.5 fF). Since the evolution of the sensor response is based on the diffusion of the analyte into the sensing layer, the sensor signal could be fitted as an exponential function [25,27,36], especially for low concentration of R.H. when the diffusion coefficient can be assumed to be constant. Over a 10-20% step of R.H., a time constant s = 1.5 s was found.…”

“…CMOS-compatible capacitive gas sensors consisting of a silicon capacitor with a specific sensing layer have been widely studied [22,[24][25][26][27]. Also, recently some research groups have expanded the field of capacitive gas sensors to foil substrate, maintaining the use of standard technology for patterning [28,29].…”

“…On one hand, it has been demonstrated that the thickness of the sensing volume in IDE capacitive gas sensors coincides with the pitch of the IDE for maximum sensitivity [34,35]. The response time of such sensors, which depends on the diffusion of the analyte in such sensing volume, evolves then quadratically with this thickness [25,27,36]. Hence, IDE printed with large pitch due to low printing resolution results in sensors facing a trade-off between good sensitivity and short response time.…”

Capacitive humidity sensors based on Ni/SiNWs nanocomposites

“…This reduced the influence of equivalent resistance in sensor. Thus, the humidity sensing properties mainly embodies in the change of capacitance with the relative humidity, i.e., the prototype sensor can be equivalent to a humidity capacitor which relies on changes in the composite dielectric constant of adsorbed water vapor [19]. The decreased influence of DCR can be benefit to enhance the stability of the measuring circuit and improve the sensitivity of the sensors.…”

The Use of Different Transduction Principles for Qualitative and Quantitative Chiral Gas Analysis

“…This setup, details of which have been described in Ref. (47) can provide sharp analyte concentration steps. The analyte vapors were generated from specifically developed temperature-controlled (T = 223 to 293 K) vaporizers (53) using synthetic air as a carrier gas and then diluted as desired using computer-driven mass-flow controllers.…”