Fabrication of vertical channel top contact organic thin film transistors

Vertical channel top contact (TC) organic thin film transistors (OTFTs) have been successfully realized on Si substrates with SiO2 as gate insulators and P3HT(poly ∼3-hexylthiophene) as organic semiconductors. The active channel region was defined by a steep step through a Si etching method. Source and drain metal contacts were deposited by vacuum evaporation through a shadow mask at a high tilting angle. Top contact transistors with channel lengths 5 μm can be fabricated with a relatively simple and efficient (yield >85%) fabrication process with only two photolithography steps (two photo masks) while no need for high-resolution and precision alignment for channel definition. Measurement results showed that the vertical channel BC (bottom contact) devices have compatible performance with planar BC devices. However, vertical channel TC transistors showed improved performance with double field effect mobilities and three times larger current ON/OFF ratios than vertical channel BC devices.