Thermal Expansion Coefficient Considerations on Field-Effect Mobility of Pentacene Organic Thin-Film Transistors With an AlN Gate Dielectric

The field-effect mobility of pentacene-based organic thin-film transistors (OTFTs) with AlN as the gate dielectric was strongly affected by the substrate temperature during pentacene deposition. The field-effect mobility μ_FE extracted from the transfer characteristics for the substrate temperatures of 70 °C, 50 °C, and room temperature (RT) are 0.06, 0.18, and 1 cm²/Vs, respectively. The (001) peak position of the pentacene thin-film phase in the grazing-incidence X-ray diffraction spectra decreases from 5.75 ° (70 °C) to 5.65° (RT). The small angle reduction (-0.1°) indicates that the c-axis of the triclinic structure of pentacene is contracted due to the stress at the pentancene/AlN interface, which is supported by the shift of Raman peak at ~ 1373  cm^-1. A mechanism based on the difference of the coefficient of thermal expansion is proposed to explain the enhancement of the field-effect mobility of pentacene OTFTs at RT.