Preparation And Characterization Of Organic Thin Film Transistor Gas Sensor Research

Organic thin-film transistors(OTFTs), also called organic field-effect transistors, are a kind of organic electronic devices which are developed on the basis of inorganic field-effect transistors. The OTFTs devices, with several advantages such as lower power consumption, less weight, and smaller size, have attracted great interests and concerns of the worldwide scientific researchers since they were reported for the first time. At present, the OTFTs, whose performance has approached or exceeded the level of a-Si:H TFTs, are widely used in OLED displays and large and very-large scale integrated circuit. With the development of organic sensitive materials, organic thin-film transistors are also applied in the detection of chemical analytes and gases.In this paper, two kinds of the OTFTs with the''bottom-gate''and''bottom-contact''configuration were fabricated with poly(3-hexylthiophene)(P3HT) and pentacene as the active layer. P3HT and pentacene thin films were doposited onto a SiO2/n-Si substrate by spin coating and vacuum evaporation, respectively. The electrical characteristics of the OTFTs were investigated and its mechanism was in further discussion. Besides, the survey reveals that the OTFTs'performance is dependent on the processing techniques to a certain extent, including the quality of the insulating layer and active layer as well as the interfacial propeties.The relationship between the morphology, crystalline state of the active layer and the device performance was studied by means of UV-Vis spectrophotometer, atomic force microscopy (AFM) and x-ray diffraction (XRD). It indicates that larger crystalline area and less grain boundary can improve the performance of the OTFTs. This is why the single crystal pentacene based OTFT has higher field effect mobility than the polycrystalline device. Besides, the thin film deposition methods can also affect its morphology and crystalline state, and eventually change the device performance.Although organic thin-film transistors are widely used in many fields, there is few report about employing them as gas sensors. In the experiment the gas sensing properties of P3HT and pentacene based OTFTs exposed to different gases were tested. The results show that poly(3-hexylthiophene) based OTFTs exhibit a good level of performance particularly in terms of response repeatability and reversibility when exposed to NO2 gas. In particular, the devices show a excellent response and recovery characteristics upon exposure to NH3 gas. Besides, poly(3-hexylthiophene) based OTFTs are also sensitive to volatile organic vapors such as methanol, ethanol and n-butanol. Meanwhile, pentacene based OTFTs have a noticeable response when exposed to ethanol, but little response to methanol, CO and SO2. Moreover, the OTFTs devices possess a high sensitivity which can be adjusted by the gate-source voltage. It means that the sensitivity of the devices operated in a proper gate bias may be enhanced, which is superior to chemiresistor sensors. In the end, the mechanism of gas sensing was also discussed in organic thin-film transistor sensors.