Vertical Structure Of Organic Thin-film Transistors Preparation And Gas Sensing Characteristics

Organic thin-film transistor (OTFT) is a kind of organic electronic devices which are developed on the basis of traditional inorganic field-effect transistors(FET). Organic thin-film transistors have some advantages such as smaller volume, less weight, lower power consumption, etc. They have attracted concerns and interests of many researchers who come from all over the world, especially the metal phthalocyanine complexes (MPc) are used for sensitive layer of gas sensor, realizing the testing about harmful gas such as NO2 and Cl2. But the development of traditional organic thin film transistors which use planar-type are affected by channel length and low carrier mobility of organic materials.In this paper we use the CuPc as the organic semiconductor gas sensitive materials, and design a vertical OTFTs that its structure is consist of Cu/CuPc/Al/CuPc/Cu. The preparation process is using vacuum evaporation and sputtering by OLED coating system. When the specific gas NO2 is absorbed on the organic film of OTFT, take oxidation reaction equivalent to acceptor doping effect, make the changes of carriers in the organic film, inject the half-conductive Al-base, change the height of schottky barrier, and then drive the OTFT. Working current which is producd by the current acrossing double schottky barrier would have a change because of the quantity of carriers that come from the emitter. Using KEITHLEY 4200 semiconductor tester and gas measurement system, we achieve examining NO2 by testing change of working current in OTFT. By the researching results, the device which consists of three layers film structure shows rectifier characteristics, and it is a kind of the schottky diodes with good performance; in the gas sensitive testing of diodes, because of acceptor doping effect produced by NO2 quantity of carriers in the device would be increased as the time which put the device in NO2 increased, and then make the I-V characteristic curves have a obviously rise; according to thermionic emission theory, the schottky barrier height reduce 60meV when the device is exposed in NO2 for 28mins; by the static analysis of Cu/CuPc/Al/CuPc/Cu vertical OTFT, we find out that the OTFT present unsaturated characteristics, in addition the current between collector and emitter would be inhibited by the increase of the base voltage.