Optimizing the growth of vanadyl-phthalocyanine thin films for high-mobility organic thin-film transistors

Abstract

To achieve high-mobility organic thin-film transistors (OTFTs), growth of vacuum-evaporated vanadyl-phthalocyanine (VOPc) thin films as the active layer was studied and optimized by varying the process conditions of the substrate temperature, deposition rate, and dielectric type. On the popularly used SiO2 gate dielectric, the surface morphology of the VOPc thin film exhibited closely packed terraced grains when the substrate temperature and deposition rate were carefully controlled. The VOPc OTFTs with terraced grains on SiO2 showed a high mobility of 0.04−0.06 cm2∕V s. Terraced VOPc grains were also obtained on Ta2O5 and Al2O3∕SiO2 gate dielectrics, where larger and more regular grains were formed. As a result, a higher mobility of 0.05−0.10 cm2∕V s was obtained for the VOPc OTFT with Ta2O5, and 0.06−0.14 cm2∕V s for the VOPc OTFT with Al2O3∕SiO2. The high mobility along with the merits of good stability and low cost makes VOPc a promising candidate for applications in organic electronics.