An Electronic Nose Based on A Micromechanical Cantilever Array

139

A recently developed microcantilever probe with integrated piezoresistive readout has been applied as a gas sensor. Resistors, sensitive to stress changes, are integrated on the flexible cantilevers. This makes it possible to monitor the cantilever deflection electrically and with an integrated reference cantilever background noise is subtracted directly in the measurement. A polymer coated cantilever has been exposed to vapors of various alcohols and the resulting cantilever response has been interpreted using a simple evaporation model. The model indicates that the cantilever response is a direct measure of the molecular concentration of alcohol vapor. On the basis of the model the detection limit of this cantilever-based sensor is determined to be below 10 ppm for alcohol vapor measurements. Furthermore, the time response of the cantilever can be used to distinguish between different alcohols due to a difference in the evaporation rates.

“…4, different cantilever responses are observed, as also reported in Ref. 7. Measurements are presented on 16 l of methanol, ethanol, and propanol.…”

Section: ͑7͒supporting

confidence: 72%

Section: ͑7͒mentioning

confidence: 99%

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A microcantilever-based alcohol vapor sensor-application and response model

Jensenius

Thaysen

Rasmussen

et al. 2000

139

“…Monolithic integration of the cantileverbased transducer with readout electronics provides interesting advantages in terms of size, portability, and cost 10,11 in front of the use of optical readout techniques commonly used. [2][3][4][5][6][7][8][9] In previous works, 10 a post-complementary metal-oxidesemiconductor ͑CMOS͒ fabrication process based on a combination of electron beam lithography and direct write laser lithography has been used in order to define and release the cantilever of fully integrated mass sensors. In this letter, the mechanical structures are defined directly during the standard CMOS process used to fabricate the overall sensor ͑cantilever-based transducer plus readout circuitry ͓Fig.…”

mentioning

confidence: 99%

Monolithic mass sensor fabricated using a conventional technology with attogram resolution in air conditions

Verd

Uranga

Abadal

et al. 2007

Monolithic mass sensors for ultrasensitive mass detection in air conditions have been fabricated using a conventional 0.35 m complementary metal-oxide-semiconductor ͑CMOS͒ process. The mass sensors are based on electrostatically excited submicrometer scale cantilevers integrated with CMOS electronics. The devices have been calibrated obtaining an experimental sensitivity of 6 ϫ 10 −11 g/cm 2 Hz equivalent to 0.9 ag/ Hz for locally deposited mass. Results from time-resolved mass measurements are also presented. An evaluation of the mass resolution have been performed obtaining a value of 2.4ϫ 10 −17 g in air conditions, resulting in an improvement of these devices from previous works in terms of sensitivity, resolution, and fabrication process complexity. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2753120͔ Cantilever-based sensors are very attractive transducers for physical, chemical, and biological sensors based on micro-/nanoelectromechanical systems 1-11 ͑NEMSs͒ due to its simplicity, wide range of sensing domains, and extremely high sensitivity when cantilever is scaled down into submicrometer scale dimensions. [6][7][8][9][10] One approach is the use of these cantilevers in dynamic mode for mass sensing applications where the mass is measured as a change of the resonance frequency. Monolithic integration of the cantileverbased transducer with readout electronics provides interesting advantages in terms of size, portability, and cost 10,11 in front of the use of optical readout techniques commonly used. [2][3][4][5][6][7][8][9] In previous works, 10 a post-complementary metal-oxidesemiconductor ͑CMOS͒ fabrication process based on a combination of electron beam lithography and direct write laser lithography has been used in order to define and release the cantilever of fully integrated mass sensors. In this letter, the mechanical structures are defined directly during the standard CMOS process used to fabricate the overall sensor ͑cantilever-based transducer plus readout circuitry ͓Fig. 1͑a͔͒, without the need of any additional lithographic process. 12 The reported results corresponding to calibration, real time mass measurements, and resolution analysis indicate the benefits in terms of resolution and operation stability of a fully integrated mass sensor operating in air conditions, which has been fabricated using a conventional CMOS technology.Cantilever structures 10 m long ͑l͒, 600 nm wide ͑w͒, and 750 nm thick ͑t͒ ͓Fig. 1͑b͔͒ have been fabricated by using the top metal layer of a commercial 0.35 m CMOS technology. 12,13 We use a three-electrode configuration constituted by the cantilever that is biased at a dc voltage ͑V dc ͒ and two electrodes for electrostatic excitation ͑V ac ͒ and capacitive readout purposes ͑V sense ͒, respectively. The cantilever displacement is detected with a full-custom designed readout CMOS circuit with a high-sensitivity and low-noise front-end stage. 14 The electrical scheme used presents an input capacitance as low as 11 fF and an input refereed noise of 21 nV/ Hz...

“…They are employed as the principal sensing element in scanning probe microscopy, 1,2 the detection of chemical or biological analytes in gases or liquids ͑hydrogen, 3 alcohol, 3,4 DNA, 5,6 antibody, 7 Bacillus subtilis spores 8 ͒, calorimetry, 4,9 humidity, 4 and pH ͑Ref. 10͒ measurements, and flow sensing.…”

mentioning

confidence: 99%

Microcantilever mechanics in flowing viscous fluids

Jana

Raman

Dhayal

et al. 2007

Microcantilevers are often deployed in flowing fluids to measure local flow velocities or to detect rapidly the nanomechanical binding of trace quantities of target analytes. The authors investigate the flow-induced mechanics of microcantilevers by deriving a semianalytical theoretical model for the nanoscale deflections of an elastic microcantilever due to a laminar viscous flow incident upon it. Conversely, the model allows for the estimation of the local flow velocities based on measured microcantilever deflection. Careful experiments performed on silicon microcantilevers in flowing nitrogen confirm the theoretical predictions up to a critical flow rate, beyond which unsteady flow-induced vibrations are seen to occur.