The electrical characteristics of pentacene-based organic field-effect transistors with polymer gate insulators

We have studied the electrical characteristics of pentacene field-effect transistors with the polymer insulators such as polymethyl methacrylate (PMMA) or poly-4-vinylphenol (PVP). The dependence of the field-effect mobility on the electric field and the temperature were measured to understand the conduction mechanism in the pentacene thin film. The transistor with PVP gate insulator shows higher field-effect mobility, μFET=0.15 cm2/V s, and smaller threshold voltage, VT=1.9 V, compared with the transistor with PMMA. The higher mobility of pentacene on PVP is attributed to the larger grain size, as observed by the atomic force microscope (AFM) images. The transistor with the PVP gate insulator shows less field dependence, implying less trap concentrations. In addition, it shows a thermally activated behavior with an activation energy of about 49 meV at high temperature and temperature independence at the low temperature, implying that the conduction process is governed by hopping mechanism at high temperature, while it is predominantly limited by a tunneling process through the grain boundaries.