Fabrication And Characteristic Study Of Sensors Based On Organic Thin-film Transistors

Organic thin-film transistors （OTFTs） have attracted extensively attention in thepast decades owing to its unique properties, such as low-cost, easy-prepared andlarge-area fabrication capability. Sensors based OTFTs in recent years have also becomean attractive choice because of the development of low cost portable sensing systemswith capabilities of multi-parametric responses. Besides, OTFTs based sensors showremarkable response repeatability, offer high selectivity by choosing certain chemicallyor biologically functionalized organic semiconductor towards a broad range of analytes,and enable sensing switch with a gate enhanced sensitivity. The main work of this paperis the following aspects:a) Based on pentacene active layer and low cost poly （merthyl methacrylate）（PMMA） insulator were fabricated with a structure of bottom contact organic thin-filmtransistor （OTFT）, and they exhibited a good linear and saturation region by test. whengate voltage VGSkept at-40V and the VDSreached-40V, the saturation current IDSwasabout6μA. The current on/off ratio was about10³to10⁴and the threshold voltage wasabout-12V, and the hole mobility of the OTFT was calculated to be0.06cm²/V.s with adefined channel length L=200μm and channel width W=1cm.In experiment, the gas sensing properties of pentacene-OTFT exposed to HCHO,NH₃, CH₄and so on were tested. It turned out that pentacene-OTFT displayed goodreversibility and recovery. In the meaning time, pentacene-OTFT didn’t exhibitreversibility and repeatability when the transistor exposed to H2、CO、CO2、SO2. Maybebecause the gas permeating into organic layer changed the thin film morphology oforganic pentacene-OTFT.b) Based on P3HT active layer was fabricated with a structure of top contactorganic thin-film transistor （OTFT） by an innovative spray technology which fit forlarge-scale production, cost-efficiency and easy-prepared. They exhibited a good linearand saturation region by test, and the saturation current was about0.2μA. The currenton/off ratio was about10³to10⁴and the threshold voltage was about-5V, and the hole mobility of the OTFT was calculated to be1.28×10^-3cm²/V.s.The light sensing properties of P3HT-OTFT exposed to illumination were testedunder simulating illumination at an intensity of100mW/cm². It turned out that IDShad adrastic increase in the presence of simulative solar, then achieved a stable state in asecond. In the meaning time, IDSalso had a drastic decrease in the absence of simulativesolar, and then it achieved a stable state after a while. It could be seen that theseresponses were remarkable and exhibited a good degree of reversibility and repeatability.Meanwhile, based on PMMA and PS different insulator devices were fabricated. Wefound the performance of devices based on PMMA insulation significantly superior todevices based on PS. The devices based on PS-pentacene-PhotOTFTs had the sameresponse recovery curve with PMMA-pentacene-PhotOTFTs under the condition ofsimulated illumination, IDShad a increase in the presence of simulative solar, IDSalsohad a decrease in the absence of simulative solar. Furthermore, the devices based on PS-PhotOTFTs need shorter recovery time than PMMA-PhotOTFTs achieve a stable state.Preliminary, we deduced that the devices of PS-OTFTs had better photosensitiveproperties than PMMA-OTFT.