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Show 90 Kevin Davenport college of science The study of organic semiconductors serves to usher in an era of cheap, easily manufactured electronic de-vices that can be made transparent and flexible. It is therefore important to study the electrical properties of these organic materials to find which can be used to build the most efficient devices possible. While the DC characteristics of many materials have been extensively studied, the AC properties have not. To this end, we have begun to explore the AC properties of organic field effect transistors based on a single, high-mobility crystal of rubrene, provided by the Podzorov group at Rutgers University. Drain and source electrodes are connected via liquid graphite and the metal-oxide gate electrode is insulated from the rubrene crystal by a 1μm thick parylene dielectric. The biasing voltage was set to a constant 5V and a 350mVp AC waveform was introduced on top of that.Our results stem from a frequency sweep of 1 Hz to 10 MHz. In addition, the transistor's gate voltage, VG, was varied, assuming values of -5V, -10V, -20V, -30V, -40V and -50V. We were primarily interested in the resistive and capacitive properties of the sample. We observed a strong spike in the magnitude of the device impedance, occurring first near 5.6kHz, when VG = -5V, and shifting up the frequency spectrum as VG increased, to a maximum of 49 kHz. In addition, the amplitude of the spike decreased as VG increased. This structure suggests some sort of RLC resonance, implying VG-dependent inductive behavior. The device admittance was seen to decrease with frequency, bottom-ing out as the impedance spiked. Both impedance and admittance converged to the same values after the peak, occurring in the MHz range, independent of VG, implying an upper limit in which the capacitive coupling of our measuring device took over. The next step of the project is then to construct an equivalent RLC circuit with which to model the device behavior and better calibrate our measurement device. In addition, a physical explanation of the observed effects must be found so that we can build a more-efficient device. AC Charac teristics of Single-Crystal Organic Field Effect Transistors Kevin Davenport (Andrey Rogachev) Department of Physics and Astronomy University of Utah UNDERGRADUATE RESEARCH ABSTRACTS Andrey Rogachev |