Preparation And Characteristics Research Of OTFT Gas Sensor Based On Bilayer Sensitive Films

In recent years, organic thin-film transistors(OTFT) have received extensive attention and been used as one of basic electronic elements in all kinds of fields. In this paper, bottom-gate and bottom-contact OTFTs gas sensors based on bilayer organic gas-sensing films were fabricated. N+ silicon wafer and the thermal oxidation silicon dioxide(SiO2) were taken as the gate electrode and insulator layer, respectively. The titanium/aurum(Ti/Au) bilayers were prepared as the source-drain electrodes with interdigital structure, in which the ratio of channel width to length was 160.A few organic gas-sensing materials were selected, and the OTFT gas sensors based on multi-walled carbon nanotubes(MWCNT)/α-Sexithiophene(α-6T) bilayer and hexadecafluorophthalocyaninatocopper(F16CuPc)/copper phthalocyanine(CuPc) bilayer films which were taken as active bilayer were prepared, respectively. Firstly, MWCNT organic dispersion was spray-deposited onto SiO2 layer, and the effect of the different volume(0.02 ml, 0.04 ml and 0.06ml) of MWCNT on the property of devices was studied to get the appropriate thickness of MWCNT film. Then, 90 nm α-6T film was deposited onto MWCNT film by vacuum evaporation to prepare bilayer films OTFT. Combined with the morphology characterization of scanning electron microscope, the electrical and gas-sensing properties, MWCNT/α-6T bilayer OTFT gas sensors was compared with α-6T single layer OTFT.N-type F16 CuPc film and p-type CuPc film were deposited onto SiO2 insulator layer by the vacuum evaporation successively to prepare bilayer films heterojunction OTFT gas sensor. The influence of CuPc film thickness on the electrical and gas-sensing properties of these devices was investigated. At last, OTFT gas sensor array was designed and prepared to detect some testing gas.Experimental results showed that both groups of OTFT devices showed good electrical and gas-sensing properties. And 0.04 ml was the most suitable volume for the MWCNT OTFT gas sensor. The OTFT device based on MWCNT/α-6T bilayer performed better electrical properties, better stabilities and higher NO2-sening response values than that with α-6T single layer, in which both the carrier mobility(μ) and on/off current ratio were enhanced two order of magnitude. The improved performance of MWCNT/α-6T bilayer OTFT was supposed that MWCNT with the high conductivity acted as highly conducting bridges among the crystalline terraces of α-6T and improved the electrical properties of OTFT. Therefore, the OTFT gas sensors based on MWCNT/α-6T bilayer organic thin-film showed superior performance. It was also found that the grid current(IGS) would also change when the tested gases were introduced. Therefore, IGS could also be selected as a characterization parameter of OTFT gas sensor.The comparative study of several thicknesses of F16CuPc/CuPc bilayer OTFT devices showed that the device based on 40 nm F16 CuPc and 15 nm CuPc exhibited the better electrical and gas sensing properties. However, the recovery ability of F16CuPc/CuPc bilayer heterojunction sensor was a little poor, which should be improved further. Finally, four OTFT devices with different sensitive materials were prepared to detect NO2. Parameters information of each device was obtained and taken to a preliminary comprehensive analysis.