We report on low voltage and high frequency vertical organic field-effect transistors (VOFETs) using silver nanowires (AgNWs) as intermediate grid electrode (source) deposited through Mayer rod-coating. The optimized AgNWs electrodes deposited on insulator surface followed by low thermal annealing have sheet resistance of~30 U/sq and surface roughness of 70 ± 20 nm. Crosslinked poly(vinyl alcohol) is used as gate insulator and C 60 fullerene as n-type channel semiconductor. Our VOFETs have high output current density of 2.5 mA/cm 2 and on/off ratio of 5 Â 10 3 with supply voltages up to 2 V. A fast switching performance of sub-1 ms at frequency gate modulation of 0.13 MHz is demonstrated. Moreover, our devices are produced based on low-cost methods compatible with industrial-scale production of organic electronics.
Sol-gel spin-coating SnO 2 thin films were deposited and processed through positive photolithography (liftoff), avoiding surface interaction with gaseous oxygen species and leading to samples with higher stability and data reproducibility, when submitted to electrical characterization. Processing includes: (1) a narrow conduction channel, (2) the assembly of electric contacts by ultrasound soldering, (3) deposition of an insulating layer, preventing the surface contact with atmospheric oxygen, which contributes for reliable measurements and the possibility of measuring SnO 2 matrix properties without influence of adsorbed oxygen. Lightly Er-doped SnO 2 sample (0.05 at.%), processed by this manner, has allowed the observation of a maximum about 50 K, in the temperaturedependent resistivity curve, which has not been found previously. This result is probably related to the combination of free electron concentration, which grows with temperature, and the grain boundary scattering, which decreases with temperature, and is the dominant mechanism for sol-gel SnO 2 . The processing also assures a remarkable reproducibility in the decay of photo-induced conductivity, yielding reliability to apply a modeling for the determination of important decay parameters, such as capture energy and grain boundary potential barrier.
Alternative materials for use in electronic devices have grown interest in the past recent years. In this paper, the heterojunction SnO 2 /Al 2 O 3 is tested concerning its use as a transparent insulating layer for use in FETs. The alumina layer is obtained by thermal annealing of metallic Al layer, deposited by resistive evaporation technique. Combination of undoped SnO 2 , deposited by sol-gel-dip-coating technique, and Al thermally annealed in O 2 -rich atmosphere, leads to fair insulation when the number of aluminum oxide layers is 4, with 0.3% of the current lost through the gate terminal as leakage current. This insulation is not obtained for devices with alumina layer treated for long time, under room atmosphere, due to degradation of the insulating film and interfusion with the conduction channel even using Sb-doped SnO 2 . The annealing of Al deposited on soda-lime glass substrate leads also to the formation of a Si layer, crystallized at Substrate/Al 2 O 3 interface. The conclusion is that for an efficient insulation the thermal annealing must be short and then, O 2 -rich atmospheres are preferred.
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