Development of semiconductor gas sensor ultra-sensitive in ppb level

为了开发具有非常高灵敏度的气体传感器，已经认识到控制这种类型的传感器的灵敏度（传感器响应）的三个关键因素，即，受体功能、转导功能和效用因子。当考虑到目标气体（还原气体）在其扩散到传感器装置中的途中与氧化物表面反应时，最后一个因素的重要性变得明显。本研究从以上三个因素出发，探索了敏感材料的新的制备方法，由SnO_2纯溶胶制备的薄膜具有相当小的孔径。然后，通过在SnO_2溶胶中分散不同量的聚乙二醇（PEG），对SnO_2溶胶的孔结构进行了改性。在相同的旋涂条件下，随着PEG含量的增加，薄膜对H_2的响应增加，同时薄膜的孔径也增大，但薄膜的H_2响应随PEG含量的增加而增大。 关于我们 在这种情况下，膜厚度相应地增加。我们尝试在溶胶中生长SnO_2晶粒，并通过调节水热处理条件，成功地实现了溶胶中SnO_2晶粒的生长。目前，已制备出晶粒尺寸为16 nm左右的单分散SnO_2溶胶。结果表明，随着微晶尺寸的增大和孔径的增大，薄膜对H_2的响应有明显的提高。此外，对H_2S的响应，更强烈的微晶尺寸和膜厚度的依赖性被披露的传感器。这种气体的分子量比H_2大，同时它在氧化物表面上的反应性也更强。我们研究了由Co_3O_4（通常为0.5wt%）-SnO_2复合粉末制成的厚膜的传感器响应。这里感兴趣的是，响应，特别是对CO的响应，随着球磨时间的增加而急剧增加。事实证明，响应的促进几乎与孔径的增加平行。因此，扩大的孔隙将使其更有利于CO分子扩散通过膜，导致极大的响应。比较了目前报道的几种SnO_2基器件对不同浓度CO的响应。本薄膜的显著大的响应似乎确保传感器响应与微结构的相关性。我们还研究了用于检测其他气体的气体传感器。少

In order to develop gas sensors for very high sensitivity, three key factors have been recognized to control the sensitivity (sensor response) of the sensors of this type, i.e., receptor function, transducer function and utility factor. The importance of the last factor is made obvious when one considers that the target gas (reducing gas) reacts with the oxide surface on its way of diffusion into the sensor device. In this study, we have been investigating new ways of processing for sensing materials from the viewpoint of the above three factors.The thin films derived from the neat sols of SnO_2 appeared to have pores rather small in size. It was then tried to modify the pore structure by dispersing various amounts of poly ethylene glycol (PEG) into the SnO_2 sol prior to spin-coating. It was observed that, under the same spin-coating conditions, the responses of the resulting thin films to H_2 increased with increasing PEG content, in parallel with the increase of pore size, although … More film thickness increased correspondingly in this case. Obviously larger pore sizes are favorable for increasing utility factor.We have tried to grow the size of SnO_2 crystallites in the sols and succeeded in it by adjusting the conditions of hydrothermal treatments. Now the sols of mono-dispersed SnO_2 with a crystallite size up to about 16 nm are available. We have shown that the thin films derived tend to increase sensor response to H_2 rather sharply as the crystallite size increases and the pore size increases accordingly. In addition, more strong dependence on the crystallite size and film thickness was disclosed for the sensor response to H_2S. This gas has larger molecular weight than H_2 and at the same time it is more reactive on the oxide surface as well. These features make this gas more sensitive to microstructure of the films.We have investigated sensor responses of thick films derived from Co_3O_4 (typically 0.5 wt%)-SnO_2 composite powders, which were prepared by mixing the component oxides thoroughly in a planet ball mill. What is of interest here was that the response, especially to CO, increased rather drastically with an increase in ball-milling time. It turned out that the promotion of response was almost in parallel with an increase in pore size. It follows that enlarged pores would make it more favorable for CO molecules to diffuse through the films, leading to the extremely large responses. The sensor responses to various concentrations of CO are compared among several SnO_2 based devices so far reported. The outstandingly large responses of the present film appear to assure the relevance of sensor response with microstructure.We investigated also gas sensors for detecting other gases. Less