Micrometer-and Nanometer-Sized CuPc Single Crystalline Field Effect Transistor For Gas Sensor Applications

Organic field effect transistor gas sensors have attracted much attention, because ofseveral advantages over resistors, such as high sensitivity，easy to integrated and reversiblemulti-parametric, apart from the great advantage of being operated at room temperature.However, carrier trapping，charger doping， molecular reorientation，dipole formation，anda range of possible chemical interations are among the many phenomena that can occur at theorganic material/solid dielectric interface and degrade device performance and stability.Moreover, the the most sensitive conductive channel of the traditional solid dielectric FETs iscapped by the semiconductor layer and the solid dielectric, so that the performanceimprovement of the transistors gas sensors are blocked. In contrast, the gas dielectric makesthe conductive channel exposed to the detected gas, which will not only facilitates the directinteraction between the gas molecules and the conductive channel resulting in theimprovement of the sensing performance，but also provides a pristine interface to reduce theinterface defects, weaken the carrier trapping, make the intrinsic charge transport possible,and minimize the Fr hlich polaron effect at the interface and improve device stability. As aresult, we can anticipate that the sensing performance of the sensors should be improved，suchas sensitivity, response and limit of detection etc. Furthermore, sub-micro/nanometer-sizedorganic single crystals can not only futher improvement of sesnsor performance, but alsobeneficial for investigating response mechanism.CuPc have attracted attention in organic gas sensors not only because of its exceptionalthermal and chemical stability, but also its remarkable gas sensing properties. In thisdissertation, we fabricated an OFET based on gas dielectric and sub-micro/nanometer-sizedCuPc single crystals as novel gas sensors and investigated their gas sensing properties.Themain results are as follows:1. The room-temperature gas dielectric sub-micro/nanometer-sized CuPc single crystallinefield effect transistor SO₂sensors with high sensitivity, low detection limit, fast response andcomplete recovery have been fabricated. The detect limitation is down to sub ppm levels （0.5ppm） with the sensitivity of119%and high resolution of100ppb. The response and recoverytime are only3and8min in0.5ppm SO₂, respectively. To the best of our knowledge, this isthe first demonstration of SO₂gas sensing based on Organic field effect transistor. Some ofthe sensing performances of this device are comparable to the commercialized solid electrolyte sensors. The theory analysis and comparative experiments between solid and gasdielectric devices show that the exposed conductive channel by gas dielectric is responsiblefor the sensitivity to SO₂.2. Gas dielectric sub-micro/nanometer-sized CuPc single crystalline field effect transistoras multi-parameter sensors and their response mechanism are investigated. A combination ofmulti-parameter and ture table provides a simple toure to detect NO₂, NO and SO₂selectively.These three gases were distinguished by this method successfully.3. Developed a new, simple, efficient route to enhancing performance of single crystallineOrganic field effect transistor by “gas enhancing methods”. This method is universallyapplicable.