Design and Fabrication of Batio3 Humidity Sensor Using Thick Film Screen Printing Technique

Thick film sensor technology has been recognized as an important technology in sensor manufacturing for the last decade. The technology contributes to the sensor development with the exploitation of the film itself as a primary sensing device. Most ceramic materials have been investigated as a humidity sensor mainly on porous structure prepared by thick film technology. These films have microstructure properties similar to those of sintered porous bodies, but the dimensions of the sensing devices can be reduced, which then can be used in hybrid circuits. In this work, two types of analyses will be made based on Barium Titanate (BaTiO3) dielectric material. The First one is to analysis the electrical properties of BaTiO3 material in bulk and thick film forms and second analysis is to characterize thick film BaTiO3 for a humidity sensor at room temperature. The BaTiO3 powder was prepared through solid state reaction using a raw material Barium Carbonate (BaCO3) and Titanium Dioxide (TiO2). The thick film paste was prepared by mixing an organic vehicle with the sintered powder in appropriate ratio. The paste was then screen printed onto a ceramic substrate in an interdigitated electrode pattern using DEK J1202 screen printing machine. The dielectric property of BaTiO3 was investigated by varying the frequency in the range of 10Hz to 10 MHz using the Impedance Analyzer. The characterization of the thick film sensor with response to the Relative Humidity (%RH) was carried out in the Humidity Climatic Chamber in the range of 20%RH to 95%RH. LCR meter and PIC conditioning unit was used to measure the response of the BaTiO3 thick film sample with the changes of the Relative Humidity.. The results showed that the dielectric response of the BaTiO3 material in bulk and film samples are the same, based on the quasi dc concept. A smaller gap of interdigitated electrode pattern gave a higher response in dielectric properties compared to the bigger gap. The BaTiO3 thick film sensor showed decrement in resistance and increment in capacitance with respect to the increases of Relative Humidity (RH). The voltage-humidity characteristic of the sensor showed a good linearity and the sensor response time is faster than the recovery time. The PIC conditioning circuit is designed to convert the analogue voltage into digital value and display the measurement result through Liquid Crystal Display (LCD) to make the system more user-friendly. As a conclusion, BaTiO3 thick film shows a good promising material to be used as a humidity sensor based on thick film screen printing technology.

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