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In this work, pentacene based thin film transistors (TFTs) with different channel lengths (L¿=¿2.5, 5, 10 and 20¿µm) have been fabricated and characterized electrically. Exploiting the electrical characteristics, we have analyzed the channel length effect on the key parameters of fabricated TFTs. We found that the performance of pentacene-TFTs was enormously enhanced by the reduction of channel length .We have also examined the influence of contact and channel resistances (RC and Rch) on the electrical proprieties of fabricated TFTs, using the transmission line method (TLM). Then, we have modeled the dependence of the total resistance RT on the gate voltage VG using the grain boundary trapping Meyer–Neldel rule (GBT-MNR) model and we have successfully reproduced, the output characteristic of pentacene TFTs using the overall resistance extracted from the GBT-MNR model. Finally, in order to investigate the channel length effect on the dynamic behavior of fabricated devices, we have reported a dynamic model based on the quasistatic assumptions which were used for metal-oxide-semiconductor field-effect transistor (MOSFET). Accordingly, we have presented a simple small-signal equivalent circuit to calculate theoretically the capacitances of pentacene-TFTs for different channel lengths., Peer Reviewed, Postprint (author's final draft)

P-type organic thin film transistors (OTFTs) with different channel lengths have been fabricated and characterized by thermal evaporation using the small tetraphenyldibenzoperiflanthene (DBP) as an active material on Si/SiO2 substrate. The influence of the channel length on the electrical performance of DBP based organic thin film transistors (DBP-TFTs) prepared with bottom gate-bottom contact in the linear and saturation regimes was systematically examined in this work. All devices showed a significant increase in the output and transfer drain current as the channel lengths were decreased in the linear and saturation regimes. We have reported the variation of the electrical parameters such as transconductance (g(m)), field effect mobility (mu(lin) and mu(sat)), contacts and total resistances (R-C and R-T), threshold voltage (V-th), total trap density (N-trap), subthreshold slope (SS), the interface trap density (D-it), turn-on voltage (V-on) and the ratio current (I-on/I-off) by channel length variation which are extracted from the experimental electrical data current-voltage of DBP-TFTs. We found that the field effect mobility is extremely dependent on the channel length dimensions. We also show that for smaller channel length, it results in a good mobility and a good ratio current of the DBP-TFTs with a short channel length (good saturation mobility and current ratio mu(sat.max) = 3 x 10(-2) cm(2) V-1 s(-1),1.6 x 10(4), respectively, for L = 2.5 mu m). The developed model shows a good agreement with the measured data for all values of channel lengths (L)., Peer Reviewed, Preprint

A series of inverted-staggered (top contact) p-channel organic thin film transistors based on small molecule tetraphenyldibenzoperiflanthene (DBP) as an active layer have been fabricated by thermal evaporation at different substrate temperatures (300, 330, 360 and 390 K). In this work, these devices have been electrically characterized at different temperatures from 300 K to 370 K in steps of 10 K under vacuum. The influences of the temperature on the electrical performance of DBP-TFTs have been investigated in saturation regime. We found that the p-channel DBP-TFTs deposited at a substrate temperature (Tsub = 390 K) exhibited a better performance under a measurement temperature of 370 K, where µFET, Vth and the ratio current were approximately 8.5 × 10- 4 cm2 V- 1 s- 1, - 0.33 V and 3 × 106, respectively. The field effect mobility of these types of devices is strongly dependent on temperature and follows the simple Arrhenius law. Additionally, the temperature-dependent electrical measurements performed on these devices reveal a thermally-activated behavior for each substrate temperature. This suggests that the charge transport in the examined devices occurs via hopping between localized states. The obtained results demonstrate well that the deposition conditions of organic active layer can improve well the device performance. Finally, an analytical model has been developed to reproduce the dependence of the total resistance and the current-voltage characteristics with the temperature and to understand the charge transport in the DBP-TFTs. The obtained data are in good agreement with the experimental results for all fabricated devices., Peer Reviewed, Postprint (author's final draft)

Bottom-contact p-type small-molecule copper phthalocyanine (CuPc) thin film transistors (TFTs) with different channel lengths have been fabricated by thermal evaporation. The influence of the channel length on the current-voltage characteristics of the fabricated transistors were investigated in the linear and saturation regimes. The devices exhibit excellent p-type operation characteristics. Results show that devices with smaller channel length (L = 2.5 mu m and 5 mu m) present the best electrical performance, in terms of drain current value, field effect mobility and subthreshold slope. Saturation field-effect mobilities of 1.7 x 10(-3) cm(2) V-1 s(-1) and 1 x 10(-3) cm(2) V-1 s(-1) were obtained for TFTs with channel lengths of L = 2.5 mu m and L = 5 mu m, respectively. Transmission line method was used to study the dependence of the contact resistance with the channel length. Contact resistance becomes dominant with respect to the channel resistance only in the case of short channel devices (L = 2.5 mu m and 5 mu m). It was also found that the field effect mobility is extremely dependent on the channel length dimension. Finally, an analytical model has been developed to reproduce the dependence of the transfer characteristics with the channel length and the obtained data are in good agreement with the experimental results for all fabricated devices., Peer Reviewed, Postprint (author's final draft)

P-type organic thin-film transistors (OTFTs), in which the active semiconductor is made of pentacene with silicon dioxide as a gate insulator, were fabricated and characterized. The effects of humidity on the electrical characteristics of pentacene based thin-film transistors (pentacene-TFTs) in the linear and saturation regimes were investigated. We report the variation of the electrical parameters by relative humidity (RH) extracted from the experimental electrical characteristics current–voltage of pentacene-TFT devices. We show that the diffusion of water molecules (H2O), the creation of acceptor states due to the presence of oxygen and the formation of clusters in the pentacene active layer considerably affect the stability and the performances of pentacene-TFTs. The degradation of electrical parameters of the pentacene-TFTs under relative humidity (RH) can be recovered with a simple pumping under vacuum (3 × 10-5 to 5 × 10-5 mbar). We also show that the changes introduced by the effects of humidity are reversible. Moreover the pentacene-TFT presents an intensive response for a high relative humidity (RH = 57%), which could be used for a humidity detection device technology., Peer Reviewed, Postprint (author's final draft)