Organic thin film transistors with multi-finger contacts as voltage amplifiers

Low-voltage p-type organic transistors with two types of multi-finger source/drain contacts were fabricated on glass and polyethylene naphthalate (PEN). They exhibited threshold voltage between −0.3 and −0.5 V and field-effect mobility between 0.2 and 0.4 cm²/Vs. Their transconductance in saturation operation varied from 25 to 60 uS and scaled with the gate dielectric capacitance and transistor dimensions. All transistors operated beyond 1 kHz, while the transistors with the shortest channel length (L = 20 um, W = 4.03 mm) exhibited a cut-off frequency of 13.4 kHz. The transistors were used to build simple voltage amplifiers by adding a resistor R_d on the drain side of the transistor. Higher R_d required higher supply voltage V_dd but resulted in increased voltage gain. A voltage gain in excess of 8 V/V was obtained for V_dd of −12 V and R_d of 220 kohm when transistor with medium value of transconductance of 37 uS was used. Consequently, the voltage gain of 10 V/V is achievable, making such transistor structures viable for sensor development.