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. 2009;9(2):869-80.
doi: 10.3390/s90200869. Epub 2009 Feb 10.

Manufacture of a Polyaniline Nanofiber Ammonia Sensor Integrated with a Readout Circuit Using the CMOS-MEMS Technique

Mao-Chen Liu  1 , Ching-Liang Dai, Chih-Hua Chan, Chyan-Chyi Wu
Affiliations

Manufacture of a Polyaniline Nanofiber Ammonia Sensor Integrated with a Readout Circuit Using the CMOS-MEMS Technique

Mao-Chen Liu et al. Sensors (Basel). 2009.

Abstract

This study presents the fabrication of a polyaniline nanofiber ammonia sensor integrated with a readout circuit on a chip using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and a post-process. The micro ammonia sensor consists of a sensing resistor and an ammonia sensing film. Polyaniline prepared by a chemical polymerization method was adopted as the ammonia sensing film. The fabrication of the ammonia sensor needs a post-process to etch the sacrificial layers and to expose the sensing resistor, and then the ammonia sensing film is coated on the sensing resistor. The ammonia sensor, which is of resistive type, changes its resistance when the sensing film adsorbs or desorbs ammonia gas. A readout circuit is employed to convert the resistance of the ammonia sensor into the voltage output. Experimental results show that the sensitivity of the ammonia sensor is about 0.88 mV/ppm at room temperature.

Keywords: Ammonia sensor; CMOS; Polyaniline; readout circuit.

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Figures

Figure 1.
Figure 1.
Schematic structure of the ammonia sensor integrated with readout circuit.
Figure 2.
Figure 2.
Energy band diagram of the sensor in (a) air and (b) ammonia. EF is the Fermi level, Ec-PANi is the conduction band of polyaniline, Ev- PANi is the valence band of polyaniline, EFi-PANi is the intrinsic Fermi level of polyaniline, Ec-PolySi is the conduction band of polysilicon, Ev-PolySi is the valence band of polysilicon, and EFi-PolySi is the intrinsic Fermi of polysilicon.
Figure 3.
Figure 3.
Readout circuit for the ammonia sensor.
Figure 4.
Figure 4.
Design of the operational amplifier circuit.
Figure 5.
Figure 5.
Frequency response of the operational amplifier.
Figure 6.
Figure 6.
Simulated results of the readout circuit.
Figure 7.
Figure 7.
Process flow of the ammonia sensor; (a) after the CMOS process, (b) etching sacrificial layers, and (c) coating the sensing film.
Figure 8.
Figure 8.
photograph of the integrated ammonia sensor chip after the wet etching process.
Figure 9.
Figure 9.
Scanning electron microscope image of polyaniline nanofiber film.
Figure 10.
Figure 10.
Elements of polyaniline nanofiber film measured by energy dispersive spectrometer.
Figure 11.
Figure 11.
Relation between the resistance variation and NH3 concentration for the ammonia sensor.
Figure 12.
Figure 12.
Measured results of the ammonia sensor with input voltage of (a) 1 V, (b) 2 V and (c) 3 V.
See this image and copyright information in PMC

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