Alignment Control of Patterned Organic Semiconductor Crystals in Short-Channel Transistor Using Unidirectional Solvent Evaporation Process

The patterning deposition of highly crystalline organic semiconductor films is a key issue in achieving high-mobility organic thin-film transistor (OTFT) arrays and circuits with practical device dimensions. However, it is generally difficult to obtain uniform crystalline films only on the desired channel regions over a large-area substrate. The alignment control of crystalline domains decreases size variations in the crystalline film. Herein, we present a patterning scheme that can control the alignment direction of solution-grown organic crystals. We employed a simple coating method combining drop casting and lamination coating. By creating a striped pattern of solventwettable/solvent-nonwettable regions on a polymer dielectric, we grew nearly uniaxially aligned ribbon-like crystals with a length of 100 μm order within a confined channel region. Bottom-contact short-channel TFTs fabricated on such a stripe pattern showed a high mobility of up to 1.5 cm²/Vs. The proposed method is compatible with the fabrication of OTFTs over an arbitrary large area.