Measurement and theory are presented for accumulation mode P3AT TFTs with Schottky and ohmic contacts. The polymer has been allowed to turn p type through exposure to air. Sample characteristics for gold contact TFTs are presented. Mobility values are 0.2 cm~2/Vs and are comparable to the best reported. Using Schottky contacts as the source and drain electrodes can reduce off currents due to the existence of potential barriers at the contact. The presence, however, of the Schottky depletion region changes the mode of operation. A model is presented to describe the sub-threshold and gradual channel regions. Devices constructed using titanium show good agreement with the model. Transconductance for these devices is reduced when compared to ohmic contact devices with calculated mobilities of 0.01 cm~2/Vs. Much smaller channel lengths are, however, possible in this technology. Off currents are found to be completely independent of gate voltage indicating good control of the off current by the Schottky junctions. Little or no gate modulation has been observed, to date, for aluminium and chromium contact devices.
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