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.
Highlights
Ammonia (NH3) is emitted by human activity
In order to characterize the variation of resistance in the sensing part, the ammonia sensor was tested without readout circuit
The results showed that the resistance of the ammonia sensor increased as the concentration of ammonia increased
Summary
Ammonia (NH3) is emitted by human activity. For instance, production of refrigeration systems and fertilizers emits ammonia. Lee et al [8] fabricated a micro ammonia gas sensor using a bulk micromachining technique. Utilized a post-CMOS process to manufacture a micro-hotplate-based gas sensor array. Llobet et al [10] utilized silicon process technology to make an ammonia sensor, in which the sensor consisted of a heater, an interdigital electrode, a temperature meter and a sensing film. Li et al [11] presented a micro gas with piezoresistive SiO2 cantilever beam fabricated by a surface and bulk micromachining process. Several microdevices manufactured by the CMOS-MEMS technique need a post-process to coat the functional films or release the suspended structures. We employ the CMOS-MEMS technique to fabricate a polyaniline nanofiber ammonia sensor integrated with a readout circuit on a chip, which can reduce the volume and cost and enhance the performance. The area of the integrated ammonia sensor chip is about 0.6 mm
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