The first solid-state field-effect transistor has been fabricated utilizing a film of an organic macromolecule, polythiophene, as a semiconductor. The device characteristics have been optimized by controlling the doping levels of the polymer. The device is a normally off type and the source (drain) current can be modulated by a factor of 102–103 by varying the gate voltage. The carrier mobility and the transconductance have also been determined to be ∼10−5 cm2/V s and 3 nS, respectively, by means of electrical measurements.
A thin-film transistor (TFT) with high carrier mobility has been fabricated using precursor-route poly(2,5-thienylenevinylene) (PTV) as semiconductor. The carrier mobility has been determined to be 0.22 cm2/V s, which is in the same level of that of amorphous silicon TFT. It has also been made clear that the carrier mobility is linearly proportional to the conversion ratio from the insulated precursor polymer to π-conjugated PTV. The π-conjugation length is crucial to obtain high carrier mobility in π-conjugated polymer TFT.
A Schottky type diode has been constructed with the electrochemically prepared copolymer having pyrrole and N-methylpyrrole units and a low work function metal (In). The heat treatment of the copolymer in air was performed in order to stabilize the electrical characteristics of the device before the deposition of a blocking electrode. The electrical properties have been investigated by means of I–V and C–V measurements. The diode quality factor and the barrier height have been obtained to be n=1.2 and ψb=0.81 V by applying a thermionic emission theory, respectively. At high current densities in the forward direction, a space-charge-limited current has been observed. This observation would be due to the charge-injection across the thin oxidized layer which would be formed during the heat treatment of the copolymer in air. Other junction parameters have been also determined by means of C–V measurements.
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