Effect of rapid thermal annealing on pentacene-based thin-film transistors

The bottom contact pentacene-based thin-film transistor is fabricated, and it is treated by rapid thermal annealing (RTA) with the annealed temperature up to 240 °C for 2 min in the vacuum of 1.3 × 10−2 torr. The morphology and structure for the pentacene films of OTFTs were examined by scanning electron microscopy and X-ray diffraction technique. The thin-film phase and a very small fraction of single-crystal phase were found in the as-deposited pentacene films. While the annealing temperature increases to 60 °C, the pentacene molecular ordering was significantly improved though the grain size only slightly increased. The device annealed at temperature of 120 °C has optimal electrical properties, being consistent with the experimental results of XRD. The post-annealing treatment results in the enhancement of field-effect mobility in pentacene-based thin-film transistors. The field-effect mobility increases from 0.243 cm2/V s to 0.62 cm2/V s. Besides, the threshold voltage of device shifts from −7 V to −3.88 V and the on/off current ratio increases from 4.0 × 103 to 8.7 × 103.

Research highlights
► The bottom contact pentacene-based thin-film transistor is treated by rapid thermal annealing.
► The pentacene molecular ordering was significantly improved though the grain size only slightly increased after the annealing temperature increases to 60 °C.
► The RTA treatment causes grain growth along the c axis and the elimination of defects and misoriented crystallites in the pentacene layer.
► The device annealed at temperature of 120 °C for 2 min exhibits properly electrical characteristics.