Improve The Field Effect Mobility Of OTFT By Using Organic Hole Transport Materials

Since1986, the first polythiophene organic thin film transistor was fabricated. Organicthin film transistor received lots of attention because of its series of advantages, such as lowcost, many kinds of the active layer materials, simple preparation process. It can achieve fullorganic, so the device has the advantage of large area, light weight, flexible. Applications ofthese devices include switching devices for active matrix flat panel displays, sensors,radio-frequency identification tags, and integrated circuits. It plays an important role inpeople’s lives.In this paper, We are committed to enhance the mobility of organic thin film transistors.We studied the material of the insulating layer, an active layer material, the source and drainelectrode materials affect the properties of the organic thin film transistor in chapter two. Firstwe prepared the insulating layer of PMMA, its thickness is1150nm and RMS roughness is0.3nm. The film has a good surface morphology conducive to the carrier transport betweenthe active layer and the insulating layer interface. Second we studied the effect of pentaceneand zinc phthalocyanine molecular structure to the field-effect mobility of organic thin filmtransistors using vacuum vapor deposition method. The result show pentacene molecules havelarger grain, larger grain reduced the number of grain boundaries and reduced the grainboundary scattering of charge carriers. It play a positive role in enhancing the mobility,Therefore, the mobility of the organic thin film transistors based on pentacene is more thantwice based on zinc phthalocyanine.Finally we studied the influence of Au and Al electrode on pentacene-based organic thinfilm transistor. Due to the different work functions of the two materials, Charge carriersinjected into the active layer from Al need to cross a barrier of0.7eV, but Au electrode canachieve well carrier injection.We have studied the surface morphology and injection barrier effect on the contactresistance in chapter three. First we introduced organic hole-transporting materialN,N-Dipehnyl-N,N-di(m-Tolyl)benzidine between the pentacene thin film and thesource-drain electrodes. This can improve the surface morphology of the active layer between source and drain contact interface. This can conducive to the formation of ohmiccontact and enhance the performance of the device, but there is a level barrier of0.4eV. Tofurther optimize the device， we used pentacene dopedN,N-Dipehnyl-N,N-di(m-Tolyl)benzidine instead of N,N-Dipehnyl-N,N-di(m-Tolyl)benzidine.Finally we prepared an optimization device, its mobility was0.31cm2/V s, threshold voltagewas-30.1V, and on/off current ratio was1.3×103.Compare to pure pentacene device, itsmobility and on/off current ratio improved three times, threshold voltage reduced4.5V.