Fabrication and application of a novel four-terminal hybrid organic/inorganic field-effect transistor for volatile organic compounds sensing

The potential application of a novel hybrid organic/inorganic volatile organic compounds sensor for commercialization and scientific research is presented. This sensor can operate both in the commonly used ‘organic thin-film transistor’ (OTFT) and ‘chemical field-effect transistor’ (CHEMFET) sensing modes as well as in a new, potentially useful sensing mode, referred to as ‘chemical memory’ mode. Compared to existing commercially available sensors, organic thin-film transistors (OTFT) show promising advantages of being cheap and easy to manufacture, light and portable, and easy to integrate in electrical circuits. However, OTFTs still operate at high voltages and lack sensitivity. This thesis will present the OTFT with patterned gate, which will eliminate the restrictions common OTFTs face. With this approach increased sensing responses are achieved. Furthermore, the sensor can be operated at low voltages such as 1V, making them extremely interesting for portable sensor devices. Comparisons with regard to their sensing responses of CuPc and pentacene organic thin-film transistors with different growth conditions are given as well. Additionally, the charge trapping mechanisms occurring during the sensing events are investigated. It is found that the charge mobilities are drastically reduced by more than 1/7 of their initial values, whereas the threshold voltages are only slightly affected. The threshold voltage can be independently evaluated by both the OTFT and ‘chemical memory’ modes.