CMOS Single‐chip Gas Detection Systems: Part II

Abstract

Sensor arrays based on industrial CMOS-technology combined with post-CMOS micromachining (CMOS MEMS) are a promising approach to low-cost sensors. In the first part of this article [1], the state of research on CMOS-based gas sensor systems was reviewed, and a platform technology for monolithic integration of three different transducers on a single chip was described. In this second part, the transduction principles of three polymer-based gas sensors are detailed and the read-out circuitry is portrayed. The first transducer is a micromachined resonant cantilever. The absorption of analyte in the chemically sensitive polymer causes shifts in resonance frequency as a consequence of changes in the oscillating mass. The cantilever acts as the frequency-determining element in an oscillator circuit, and the resulting frequency change is read out by an on-chip counter. The second transducer is a planar capacitor with polymer-coated interdigitated electrodes. This transducer monitors changes in the dielectric constant upon absorption of the analyte into the polymer matrix. The sensor response is read out as a differential signal between the coated sensing capacitor and a passivated reference capacitor, both of which are incorporated into the input stage of a switched capacitor second-order RD-modulator. The third transducer is a thermoelectric calorimeter, which detects enthalpy changes upon ab-/desorption of analyte molecules into a polymer film located on a thermally insulated membrane. The enthalpy changes in the polymer film cause transient temperature variations, which are detected via polysilicon/aluminum thermocouples (Seebeck effect). The small signals in the lVrange are first amplified with a low-noise chopper amplifier, then converted to a digital signal using a RD-A/D-converter and finally decimated and filtered with a digital decimation filter.

CMOS Single Chip Gas Detection Systems — Part I

“…For the subsequent decimation to f 0 , a finite-impulse response (FIR) filter with a higher order cutoff is required. The details of the design and implementation can be found in [6]. Figure 1.4.29 shows a measurement of the output of the RD temperature sensor with curvature-corrected reference voltage.…”

“…The three transducers on the multisensor chip and the dedicated circuitry that was developed to read their small output signals will be described in [6]. In addition to the transducers, there are several building blocks that are needed in almost every smart sensor system based on CMOS-MEMS technology.…”

“…Section 1.4.4 details the circuitry building blocks, which are generally needed to realize a monolithic gas detection system: bus interface, digital controller, bias current generators, voltage references and a temperature sensor. Circuitry details of the three transducers are discussed in [6]. Section 1.4.5 shows two application examples of the multisensor chip, and Section 1.4.6 contains the outlook.…”

Characterization of the gas sensors based on polymer-coated resonant microcantilevers for the detection of volatile organic compounds

“…Polymers can be used as sensitive material for the detection of VOCs because the absorption and desorption of VOCs in polymers are in general completely reversible [12]. Polymers can be easily deposited and structured using spray coating [13,14], drop coating [15,16] or spin coating [17] methods.…”

Materialien für Sensorpolymere: Möglichkeiten kombinatorischen Designs

“…Zum Entwurf von Sensoren mit neuartigen Funktionalitäten haben sich interdisziplinäre Ansätze als erfolgreich erwiesen. Innovationen resultierten aus dem Zusammenschluss unterschiedlicher Forschungsstrategien wie kombinatorischer und Hochdurchsatzuntersuchungen1, 2 mit Mikro‐ und Nanotechnologien3–6 und Mikrofluid‐Techniken 7. Die treibende Kraft für diese Arbeiten war und ist der Bedarf an verbesserten Sensoren zur Überwachung chemischer und biologischer Prozesse 8–10.…”