Flexible Organic Thin‐Film Transistors with Silk Fibroin as the Gate Dielectric

Abstract

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...

Silk Fibroin for Flexible Electronic Devices

“…When the thickness of the pentacene fi lm is thicker than 30 nm, the thin-fi lm phase, which is crucial for charge transport, becomes prominent, and the amount of the pentacene thin-fi lm phase on the silk fi broin is about four times higher than on SiO 2 ( Figure 9 f). [ 138 ] The GIXRD results indicate that a large portion of the amorphous form of pentacene is reduced by using silk fi broin as the gate dielectric, resulting in a high mobility value of 23.2 cm 2 V −1 s −1 . In comparison, a pentacene OTFT with a SiO 2 gate dielectric shows a lower mobility value of 0.22 cm 2 V −1 s −1 , due to the large percentage of amorphous phase of the pentacene.…”

“…Moreover, silk-fi broin fi lms can improve the crystallization of organic semiconductors compared with inorganic gate dielectrics. A fl exible pentacene OFET on PET substrate has been reported, utilizing a silk-fi broin thin fi lm as the gate dielectric ( Figure 9 a,b), [ 138 ] which is characterized by a high mobility value of 23.2 cm 2 V −1 s…”

“…The enhanced performance of the pentacene OFET with a silk gate dielectric not only arises from the ability of fi broin to improve the crystallinity of semiconducting materials, [ 138,140 ] as fi broin itself also contributes signifi cantly to the carrier mobility of the OFET. The structure of silk fi broin comprises a collection of antiparallel β-strands with the direction of the polypeptide backbone extending along the fi ber axis.…”

Increased electrical conductivity of peptides through annealing process

“…The device showed possibility to be used as a p-type semiconductor, with an on/off current ratio of 4.6(±1.0) and a field-effect mobility of 4.9(±1.6) × 10 5 cm 2 V 1 s 1 for a 600°C annealed peptide FET. Although poor device performance was obtained, it is meaningful because so far many types of biologically occurring polymers have shown an insulating property, 22,23 and annealed materials have shown a conducting property. 24,25 The chemical structure of the starting-peptide material, YYACAYY, is depicted in Fig.…”

Análise do desempenho elétrico de transistores orgânicos visando a fabricação sobre substratos flexíveis.

“…/Vs e tensão de operação de V DS = -3V, sobre substrato flexível e proteína da seda como isolante [36].…”