1/f noise in pentacene and poly-thienylene vinylene thin film transistors

We investigate low frequency conductivity noise in the drain-source channel of organic material field-effect transistors by measuring the spectra of current fluctuations for several values of the gate voltage V-gs and drain voltage V-ds and find that it is 1/f. The samples are biased in the ohmic range of the applied V-ds. The relative current 1/f noise is inversely proportional to the charge carrier numbers N generated by illumination or by varying the gate-source voltage. Hooge's empirical relation for the 1/f noise is validated for these organic semiconductors with an alpha congruent to0.01 for poly-thienylene vinylene and about 100 for pentacene thin film transistors. From geometry dependence of the noise we conclude that series resistance can be ignored for poly-thienylene vinylene field-effect transistors. However, some pentacene samples suffer from a noisy series resistance to the channel resistance. From the 1/f noise dependence on geometry and gate voltage bias we conclude that it can be used as a diagnostic tool for device quality assessment. (C) 2002 American Institute of Physics.