| Human beings are living in the highly information era, it is an urgent requirement that how fast to acquire information and deal with it. The sensor, as a source of getting information, has played an important role in the modern development society of science and technology.Porous silicon (PS) has many advantages, such as a huge specific surface area, good accommodating with the IC craft, test method is simple, easy to make into a practical sensor, low cost and easy to use. These merits enable the porous silicon to become sensor's ideal sensitive material. Applying the porous silicon to sensor has become a hot topic gradually.In this paper, the resistance type gas sensor was prepared by porous silicon which was fabricated by single cavity electrochemistry etch method and composite gas sensing film of metal/porous silicon which was fabricated by chemical deposition method. the surface morphology of porous silicon was characterized by scanning electron microscopy (SEM), the relationship between the surface appearance, pore thickness, pore size of porous silicon and the silicon chip type, the corrosion current density were also analyzed. The formation mechanism of porous silicon was discussed briefly. It is found that the porous aperture of N-type porous silicon is larger and all of them are in the micron level. To the opposite, the porous aperture of N-type is in the nano-level. The rough surface of N-type porous silicon has a good ability to deposit metal ions and adsorb gas molecules.Gas sensors of copper/porous silicon, silver/porous silicon, zinc/porous silicon devices were sensing tested respectively. It was found that the Cu/porous silicon have a good sensitive ability to the formaldehyde, ammonia, ethanol, the sensitivity was good, but the selectivity was very bad. Ag/porous silicon devices are sensitive to formaldehyde response, in 5000ppm, the sensitivity reaches 11.5. Meanwhile, silver/porous silicon devices are not sensitive to the other two gases, it is indicated the silver/porous silicon devices can be regarded as an ideal formaldehyde gas sensor by its good selectivity ability. Compared with the form two devices, zinc/porous silicon is less sensitive, not sensitive to formaldehyde and ethanol, but it is a little sensitive to ammonia. In 5000ppm, the highest sensitivity is only 2.04, poor performance. It was also found that the three kinds of sensitive components had a good stability after deposited the metal.Has obtained resistance reduction which the metal/PS gas sensorses occur is causes by the superficial sensitive material physisorption and the chemical adsorption, but chemical adsorption its leading role which occurs under the nanometer metal catalytic effect, the different metal's nano particles catalysis performance was different, has caused its gas sensitive performance difference.The resistance of surface of metal/porous silicon will change when the surface of electron density changes after adsorption of specific gas molecules. The adsorption mechanism and the effect of nanocrystalline metal particles on the gas-sensing properties were analyzed in this paper. The experiments showed that the resistance reduction of metal/PS gas sensors was caused by the physical adsorption and chemical adsorption of superficial sensitive material and the chemical adsorption which was under the catalytic by nanometer metal played a leading role. Different catalytic property of nano-metal particles result in different sensitivity to gases. |
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