1/f noise in pentacene organic thin film transistors

We report on the flicker (1/f ) noise in pentacene organic thin film transistors (TFTs) of different designs. Our studies show that the TFT design affects the noise level and the noise dependence on the gate- and drain-source biases. The measured noise level was the lowest for the TFTs with a top source and drain contacts design. For these devices, the noise dependence at low drain current values resembled that for n-type crystalline Si metal-oxide-semiconductor field-effect transistors. The extracted Hooge parameter alpha, which allows comparing the noise level in different devices and materials, was 0.045 for the top-contact TFTs. This parameter value is several orders of magnitude lower than that for conducting polymers and only several times higher than that for hydrogenated amorphous Si (alpha-Si:H) TFTs. The bottom source and drain contacts TFTs had a much higher noise level with a noise dependence on the terminal voltages that differed from the noise voltage dependence for the top-contact TFTs. The Hooge parameter values were in the range of 5-20 for the bottom-contact TFTs. We estimated that the contact noise could be comparable to the channel noise for both top-contact and bottom-contact TFTs. (C) 2000 American Institute of Physics. [S0021-8979(00)00922-1].