Effect of Calcination Temperature on Interface Properties Between In 2 O 3 and Au Electrode in Micro Gap Semiconductor G
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0915-R06-21
Effect of Calcination Temperature on Interface Properties Between In2O3 and Au Electrode in Micro Gap Semiconductor Gas Sensors Jun Tamaki1, Jun Niimi1, and Satoshi Konishi2 1
Dept. of Applied Chemistry, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu-shi, Shiga, 525-8577, Japan
2
Dept. of Micro System Technology, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu-shi, Shiga, 525-8577, Japan
ABSTRACT The In2O3 thin film micro sensors were fabricated by dropping In(OH)3 sol on micro gap electrode with 0.1-2.5 µm of gap size, dried, and calcined at various temperatures. The grain size of In2O3 and thus the number of In2O3 grains were changed by calcining at 600-850 oC. The size of grain was increased from 15 nm at 600 oC to 55 nm at 850 oC, and thus the number of grains in 0.3 µm gap was decreased from 19 to 5.3. Contrary to the expectation, the small resistance changes to both 1 ppm Cl2 (resistance increase) and 0.5 ppm Cl2 (resistance decrease) were obtained for In2O3 micro sensors calcined at 700-850 oC. These were contributed to the changes in the surface and interface chemical state to suppress the adsorption of or the substitution with Cl2 molecule. INTRODUCTION High sensitivity semiconductor gas sensors are eagerly demanded in the fields of environmental monitoring, VOCs monitoring, bad-smelling gas detection, breath analysis and so on [1]. The semiconductor gas sensor is one of promising candidates for these applications since it has a simple structure consists of a sensing oxide layer and metal electrodes for resistance measurement. Recently, we have found that the nano design of electrode structure was important for sensitizing semiconductor gas sensor [2-4]. It was observed in the NO2 detection using WO3 sensor [3] and the Cl2 detection using In2O3 sensor [4] that the gas sensitivity was increased when the size of electrode gap was decreased comparable to size of oxide grain. When the gap size is decreased, the number of oxide grains included in micro gap electrode is decreased, inducing the increasing contribution of oxide-electrode interface to total sensor resistance. The increasing sensitivity with decreasing gap size suggests the much higher sensitivity at interface (Si) than at grain boundary (Sgb). In these studies, the gap size was varied using the fixed grain size of oxide in order to investigate the micro gap effect in semiconductor gas sensors. As another idea, it is considered that the grain size is varied with fixed gap size to obtain similar gap effect. In this study, the grain size was varied by changing the calcination temperature in the Cl2 detection-In2O3 sensor system. It was found in our previous studies that the In2O3 sensor showed different responses to Cl2 gas depending on gas concentration, i.e., the resistance increase to high concentration (>1 ppm) of Cl2 and the resistance decrease to lower concentration Cl2 (
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