Study Of High Performance Low-voltage OTFTs

Organic thin film transistors (OTFTs) as a basic unit of integrated circuits have agreat application potential in the area of electronics. In recent years, much attention hasbeen paid to the study of OTFTs and great progress has been made in the areas,including flat-panel displays, radio-frequency identification tags and biological sensors.Recently, large numbers of high mobility semiconductors have been fabricated and themobility can rival that of the amorphous silicon, which has increased the applicationpotential of OTFTs greatly. Though great progress has been made, there are manychallenges remaining which limit the application of OTFTs a lot. One of thesechallenges is the high operation voltage of the devices. OTFTs with high operatingvoltage will not only result in high energy consumption but also be incompatible withmany emerging applications, including disposal sensors, flexible displays,radio-frequency identification tags and so on. Another challenge is the work instabilityof the OTFTs because of the traps distributing in the semiconductor, at the inter face ofthe semiconductor and the dielectric and in the bulk of the dielectric, which has been abig obstacle to the real application of OTFTs. Al2O3exhibits a high relative dielectricconstant that is much larger than those of the polymers used in the OTFTs before. Wesuccessfully fabricated the pentacene OTFTs and PTCDI-C13H27OTFTs employing thesolution-processed Al2O3as the gate dielectric at a relative low annealing temperature of170℃. We also made the high performance low voltage inverters using the pentaceneand PTCDI-C13H27OTFTs both on the Si and PET substrates. The electricalcharacteristics were measured by the probe station which is connected to asemiconductor parameter analyzer. The semiconductor films and the dielectric filmswere characterized by the AFM, XRD and XPS. The carrier mobility of the pentacenedevice and PTCDI-C13H27device were2.6cm2v-1s-1and0.13cm2v-1s-1respectively.Threshold voltage is one of the very important parameters of OTFTs and theunderstanding of which is of vital importance to the study of operational stability ofOTFTs. We investigated the temperature dependent threshold voltage of pentacene OTFTs and the study revealed that there is a two-stage temperature dependence of thethreshold voltage. In the range of200-210K, there is a break point which is caused bythe phase transition of the supercooled water in the devices. Based on our study, wefound that the interface of the dielectric and semiconductor is very critical to theoperational stability of the OTFTs. Then we subsequently studied the electricalcharacteristics of C60and the result shows that the device with an excellent dielectricinterface has a good operation stability and high mobility. We also investigated themobility and the bias stress effect of low voltage pentacene device on Al2O3dielectric.The result also proves that the mobility and the operation stability have close relationwith the property of the dielectric interface.The thesis is helpful in the understanding of the threshold voltage and theoperational stability of OTFTs. Additionally, it is useful to fabricate high performanceOTFTs. The study of carrier mobility and operational stability can provide valuableinformation for the real application of OTFTs.