Showing papers on "Pentacene published in 1998"

Theory of the field-effect mobility in amorphous organic transistors

Abstract: The field-effect mobility in an organic thin-film transistor is studied theoretically. From a percolation model of hopping between localized states and a transistor model an analytic expression for the field-effect mobility is obtained. The theory is applied to describe the experiments by Brown et al. [Synth. Met. 88, 37 (1997)] on solution-processed amorphous organic transistors, made from a polymer (polythienylene vinylene) and from a small molecule (pentacene). Good agreement is obtained, with respect to both the gate voltage and the temperature dependence of the mobility.

Temperature-independent transport in high-mobility pentacene transistors

Abstract: The charge-carrier transport mechanism in the organic semiconductor pentacene is explored using thin-film transistor structures. The variation of the field-effect mobility with temperature differs from sample to sample, ranging from thermally activated to temperature-independent behavior. This result excludes thermally activated hopping as the fundamental transport mechanism in pentacene thin films, and suggests that traps and/or contact effects may strongly influence the observed characteristics. These results also indicate that field-effect transistors may not be appropriate vehicles for illuminating basic transport mechanisms in organic materials.

Organic thin-film transistors for organic light-emitting flat-panel display backplanes

Abstract: The performance of organic thin-film transistors (OTFTs) has improved significantly in the last several years and it now appears likely that they will find application in low-cost large-area electronic applications. Active-matrix displays are of special interest and integration of OTFTs with organic light-emitting devices (OLEDs) in all-organic displays is particularly attractive. The device requirements for active-matrix OLED displays are very similar to those of active-matrix liquid crystal displays (AMLCDs) and can be satisfied with OTFTs fabricated using stacked pentacene active layers. Such devices have demonstrated field-effect mobility near 1.5 cm/sup 2//V/spl middot/s, on/off current ratio near 10/sup 8/, near-zero threshold voltage, and subthreshold slope less than 1.6 V/decade. These characteristics are similar to those obtained with hydrogenated amorphous silicon (a-Si:H) devices and such devices would allow the use of polymeric substrates with advantages in weight, ruggedness, and cost compared to glass substrates currently used with a-Si:H devices in AMLCDs.

Integrated a-Si:H/pentacene inorganic/organic complementary circuits

Abstract: We have developed a low-cost fabrication process for complementary circuits using integrated organic and inorganic thin film transistors (TFTs) In these circuits, a-Si:H TFTs are used as the n-channel and pentacene organic TFTs as the p-channel devices These circuits show high switching gain and excellent logic level conservation, with very low off-currents during static operation Gate delay of our circuits, measured using ring oscillators, is as low as 5 /spl mu/s, the fastest speed reported for circuits using organic transistors

Theory of the Organic Field Effect Transistor

Abstract: The performance of organic based field-effect transistors (OFETs) has considerably increased recently, and now compares to that of amorphous silicon. The operation mode of OFETs is described. It differs from that of the conventional MISFET in that it operates in the accumulation regime. Another important difference is the charge transport in organic materials, which occurs via hopping of self-localized polarons. As a result, the mobility is thermally activated and electric field dependent. Effects of this feature on the current-voltage characteristics are outlined.

Mobility of oligomeric thin film transistors prepared at rapid growth rates by pulsed laser deposition

Abstract: We present results on film transistors and related structures, prepared by pulsed laser deposition (PLD) of pentacene and thienylene–vinylene oligomers. PLD produces an improvement in electronic properties relative to conventional thermal evaporation, while allowing films to be deposited at least a hundred times faster. Atomic force microscopy reveals that the properties are associated with increases in molecular ordering. Pentacene thin film transistors having a mobility (4×10−2 cm2 V−1 s−1) and threshold voltage (0.3 V), and thus being viable for practical applications, have already been produced by PLD using room temperature substrates. Moreover, structural and conductivity data indicate that improvements will result when devices are deposited at higher substrate temperatures.

Coherence from Femtosecond Fluorescence Interference Noise-Terahertz Electronic Beatings in Pentacene

Abstract: By measuring fluctuations of fluorescence correlations in Pentacene/p-Terphenyl novel fs-beats are observed. They arise from polarisation interferences due to descrete diagonal disorder between spatially different Pentacene sites.