Organic thin-fi lm transistors (OTFTs) are promising components for fl exible and portable electronics, such as e-paper, [1][2][3] radio-frequency identifi cation (RFID) tags, [ 4,5 ] and biosensors. [ 6,7 ] OTFTs usually exhibit very low switching speed and are diffi cult to use instead of inorganic thin-fi lm transistors (TFTs), although they possess the merits of fl exibility and low cost. Several challenges for OTFTs of large area are high fi eld-effect mobility ( μ FE ), low operating voltage, and solution processing. The μ FE value and operating voltage of pentacene OTFTs strongly depend on the gate dielectric material. [8][9][10] Pentacene is usually deposited on various organic and inorganic dielectrics, such as poly(methyl methacrylate) (PMMA), poly(vinyl pyrrolidone) (PVP), SiO 2 , and AlN, using the bottom gate OTFT confi guration. [11][12][13] The reported μ FE values are in the range of 0.5-4 cm 2 V − 1 s − 1 and the operating voltages vary from -5 to -40 V. The low μ FE values are mainly limited by the quality of pentacene and the interface scattering in OTFTs. Many attempts have been made to improve the μ FE value by modifying the surface of the gate dielectric. The maximum μ FE value has been improved to ca. 6 cm 2 V − 1 s − 1 . [ 14 ] In 2004, Hosono's group reported a μ FE value larger than 10 cm 2 V − 1 s − 1 for amorphous InGaO 3 (ZnO) 5 (a-IGZO) TFTs. [ 15 ] The μ FE value is much higher than that of pentacene OTFTs. The research in fl exible electronics has focused on a-IGZO TFTs since then, especially in the fi eld of organic light emitting diodes (OLEDs). However, the fl exibility of amorphous semiconducting oxide TFTs is lower than OTFTs. An urgent requirement of fl exible electronics is to fi nd fl exible materials able to improve greatly the μ FE value of OTFTs.Here we present a pentacene OTFT made on a fl exible poly(ethylene terephthalate) (PET) plastic substrate with a very high μ FE value of 23.2 cm 2 V − 1 s − 1 in the saturation regime and a low operating voltage of -3 V. Silk fi broin was chosen as the gate dielectric and fabricated in thin fi lm form by a low-cost solution process at room temperature. The device performance is so high that the pentacene OTFTs outperform a-IGZO TFTs.Silk fi broin is one of the silk proteins emitted by the silkworm; silk fi broin forms the structural center of silk and sericin surrounds it. Silk fi broin is a natural biopolymer consisting of the repeated amino acid sequence of alternating Gly and Ala [ 16 ] ( Figure 1 a). The silk fi broin thin fi lm in our work is amorphous and its secondary structure is characterized by the Fourier transform infrared-attenuated total refl ection (FTIR-ATR) spectrum in Figure 1 b. The silk fi broin thin fi lm consists of turn (ca. 1666, ca. 1678, ca. 1690 cm − 1 ), random-coil (ca. 1642, ca. 1651 cm − 1 ), α -helix (ca. 1659 cm − 1 ), and hydrogen-bonded C = O (ca. 1704 cm − 1 ) according to the curve-fi tting results based on previously published FTIR-ATR data. [ 17 ] Silk fi broin has been used as a material fo...
This study presents carbon attachment on an aluminum nitride (AlN) gate dielectric to improve the device performance of pentacene-based organic thin-film transistors (OTFTs). This approach produces high OTFT performance on an aged AlN surface. A high mobility of 0.67 cm2/V s was achieved on an AlN surface aged for 14 days, compared to a mobility of 0.05 cm2/V s on an as-deposited AlN surface. This improvement in device performance is correlated with carbon attachment on the AlN surface, which lowers surface energy. The lowered surface energy made the surface less polar, as measured by a contact angle instrument. The chemical composition of the aged AlN surface was analyzed using x-ray photoelectron spectroscopy before pentacene deposition. Enhanced C=C bonding at 284.5 eV was observed on the aged AlN surface. These enhanced C=C bonds favored the growth of large pentacene islands in the initial growth stage, which may improve OTFT device performance.
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