Basic Research for Development of Ceramic Odor Sensors

半导体气体传感器的传感性能通过微结构控制和表面改性得到了广泛的改善。本文提出了一种新的半导体气体传感器设计思路。通过控制snO_2晶体尺寸(D)、空间电荷层厚度(L)和Pd促进剂的分散状态，提高了snO_2气体传感器的灵敏度。灵敏度随D的降低而增加，接近2L （=ca）。纯SnO_2为6 nm)，而Al^<3+>掺杂的SnO_2即使在大D下也非常高，因为掺杂带来了大的L值。因此，将D/2L控制在接近1或更小的范围内，可以提高灵敏度。另一方面，在SnO_2表面高度分散的Pd小颗粒提高了Pd-SnO_2传感器的灵敏度。钯络合物固定法是获得高分散性钯粒子的最佳方法。用外源氧化物对SnO_2表面进行修饰，提高了选择性。加入碱性氧化物如La_2O_3，可以提高SnO_2气体传感器对乙醇气体的灵敏度，这可能是由于C_2H_5OH通过CH_3CHO中间体脱氢氧化在碱性表面进行得很顺利。Pd-La_2O_3-In_2O_3元素也得到了类似的结果。另一方面，氧化铜是提高SnO_2元素对H_2S敏感性能的独特添加剂。CuO-SnO_2元素表现出极高的灵敏度和选择性，在关闭H_2S时表现出类似开关的恢复响应。CuO和cu之间的状态变化被发现是造成这种独特传感特性的原因。

Sensing properties of semiconductor gas sensor were extensively improved by microstructrure control and by surface modification. A new design concept of semiconductor gas sensor was constructed in the present research.The sensitivity of snO_2 gas sensor was enhanced by controlling crystallite size (D) and thickness of space charge layer (L) of SnO_2 and the dispersion state of Pd promoter. The sensitivity increased with decreasing D close to 2L (=ca. 6 nm for pure SnO_2), while for Al^<3+>-doped SnO_2 it was very high even at large D because the doping brings about large L values. Therefore it was found that the sensitivity could be promoted when D/2L was controlled to be close to unity or less. On the other hand, the sensitivity of Pd-SnO_2 sensor was enhanced by highly dispersing small Pd particles on SnO_2 surface. The Pd complex fixation method was found to be the most excellent method to obtain the high dispersion of Pd particle.The improvement of the selectivity was attained by modifying the SnO_2 surface using foreign oxide additives. The sensitivity of SnO_2 gas sensor to ethanol gas was enhanced by adding basic oxide such as La_2O_3, probably because the oxidation of C_2H_5OH via dehydrogenation through CH_3CHO intermediate proceed favorably on the basic surface. Similar results were obtained for Pd-La_2O_3-In_2O_3 element effectively. On the other hand, CuO was a unique additives to enhance sensing properties of SnO_2 element to H_2S. CuO-SnO_2 element showed the extraordinary high sensitivity and selectivity, and switching-like recovery response on turning off H_2S. The change of state between CuO and CuS was found to be responsible for such unique sensing properties.