High-Performance Low Voltage Organic Thin-Film Transistors
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High-Performance Low Voltage Organic Thin-Film Transistors Stijn De Vusser1 ; Soeren Steudel1 ; Kris Myny; Jan Genoe; Paul Heremans1 IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium 1 also with KULeuven, ESAT-INSYS, Kasteelpark Arenberg 10, B-3001 Leuven, Belgium
ABSTRACT In this work, we report on high-performance low voltage pentacene Organic Thin-Film Transistors (OTFT’s) and circuits. Inverters and ring oscillators have been designed and fabricated. At 15 V supply voltage, we have observed invertors showing a voltage gain of 9 and an output swing of more than 13 V. As for the ring oscillators, oscillations started at supply voltages as low as 8.5 V. At a supply voltage of only 15 V, a stage delay time of 3.3 µs is calculated from experimental results. We believe that these results show for the first time a high speed ring oscillator at relatively low supply voltages. The required supply voltages can be obtained by rectification using an organic (pentacene) diode. These results may have an important impact on the realization of RF-ID tags: by integrating our circuits with an organic diode, the fabrication of organic RF-ID tags comes closer.
INTRODUCTION During the last few years, Organic Thin-Film Transistors (OTFT’s) have been incorporated into a number of applications. To date, mostly digital circuits have been presented, as well as driver circuits for display applications [1, 2]. The interest in digital circuits can be attributed to an emerging demand for cheap radio frequency tags (RF ID-tags) [3]. OTFT’s are a promising technology for realizing this concept. The RF ID-tag has to draw its power from an RF signal it receives at its antenna. Ideally, these tags should be able to operate at a carrier frequency of 13.56 MHz, which is a standardized frequency in the field of RF ID-tags. We report here on circuits operating at relatively low supply voltages, suitable for future use in an organic RF ID-tag.
EXPERIMENTAL DETAILS OTFT’s and circuits have been processed on a glass substrate. The glass substrate (Corning Eagle2000 ) was chosen because of its very smooth surface. The RMS roughness of the substrate ˚ comparable to the was measured by atomic force microscopy (AFM), and was smaller than 5 A, roughness of a polished crystalline silicon wafer. The gate electrodes consist of a 20 nm layer of TiW, patterned by photolithography and lift-off. A layer of 100 nm sputtered SiO 2 was used as the gate dielectric. An AFM scan of this SiO2 layer on top of a gate electrode confirms that the ˚ Vertical interconnects were formed by photolithography and roughness is in the range of 5-10 A. wet etching in a buffered hydrofluoric acid solution. The source and drain metal electrodes consist of a layer of 20 nm sputtered Au, patterned by photolithography and lift-off.
H1.4.2
After a thorough cleaning step, the sample was treated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) and dodecanethiol. Both these SAM’s were deposited from the vapour phase. It is known that a treatment of the oxide s
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