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We report a low-voltage organic field-effect transistor consisting of an extended gate sensory area to detect various ions in a solution. The device distinguishes various ions by the shift in threshold voltage and is sensitive to multiple ions with various concentrations. X-ray photoelectron spectroscopy measurements and the resistance changes at the sensor area prove that the ions are doped into the sensitive film at the sensor area. Because of the effect of doping, the conductivity of the semiconductor polymer film changes thus causing a threshold voltage shift.

Metal organic pentacene based low voltage organic thin film transistors with field effect mobility as large as 0.8 c2 m /V - 1 .s -1 and on/off current ratio larger than 10 6 have been fabricated. Thin films deposited by evaporation at different deposition rate has different morphology which leads to a difference in transistor characteristics. The films with a deposition rate of 2A/sec has better morphology and also the transistor behavior. AFM (atomic force microscope) and STM (scanning tunneling microscope) were used to understand the morphology and ordering of the molecules on the silicon surface which helps the transistor to operate at low voltages. The results presented here show a strong correlation between molecular ordering and the need of well-ordered films for the performance of organic thin film transistors (OTFT's).