The transducer elements for such sensor arrays need to be small, low-power, and compatible with conventional microprocessing technology. The transducers include chemiresistive gas sensor, FET gas sensor, capacitive gas sensor, and inductive gas sensor. Of these transducers, chemicapacitors and chemiresistors are the best suited for low-power sensor arrays. The change of electrical properties such as conductance or capacitance upon exposure to analytes can be used to detect chemical and biological agents, respectively. Chemiresistors are simply implemented in many application fields, but they have disadvantages such as instability and cross sensitivity. Whereas chemicapacitors are known to provide superior sensitivity and recovery time because capacitance can response to very thin layers of chemoselective material down to a single molecular monolayer, resulting in the elimination of the duration time for capacitance change. In this work, the room-temperature capacitive ethanol gas sensing properties of AAO (anodic aluminum oxide) were studied and the underlying mechanisms were analyzed based on its electrode configuration and detection frequency. Figure 1 shows the progress of the experimental progress according to each electrode patterns and thicknesses.

The sensor sensitivity of the chemocapacitive sensor toward ethanol was affected by the humidity because it has higher dielectric constant than ethanol. Therefore, the surface treatment of AAO was carried out by silanization using APTES and HMDS. The degree of hydrophobicity of AAO surface was determined by measuring the water contact angle by the Sessile Drop method. After surface treatment was performed in each method, the sensitivity of the sensor to the wet air was also measured.

Through silanization, similar sensor sensitivity to ethanol was obtained, and at the same time, sensor sensitivity to wet air was minimized as illustrated in Figure 2. In this study, the sensor characteristics were optimized by the electrode pattern and thickness, and the gas selectivity of the sensor was improved through surface treatment.