Flexible, high mobility short-channel organic thin film transistors and logic circuits based on 4H–21DNTT

Abstract

The low mobility and large contact resistance in organic thin-film transistors (OTFTs) are the two major limiting factors in the development of high-performance organic logic circuits. Here, solution-processed high-performance OTFTs and circuits are reported with a polymeric gate dielectric and 6,6 bis (trans-4-butylcyclohexyl)-dinaphtho[2,1-b:2,1-f]thieno[3,2-b]thiophene (4H–21DNTT) for the organic semiconducting layer. By optimizing and controlling the fabrication conditions, a high saturation mobility of 8.8 cm2 V−1 s−1 was demonstrated as well as large on/off ratios (> 106) for relatively short channel lengths of 15 μm and an average carrier mobility of 10.5 cm2 V−1 s−1 for long channel length OTFTs (> 50 μm). The pseudo-CMOS inverter circuit with a channel length of 15 μm exhibited sharp switching characteristics with a high signal gain of 31.5 at a supply voltage of 20 V. In addition to the inverter circuit, NAND logic circuits were further investigated, which also exhibited remarkable logic characteristics, with a high gain, an operating frequency of 5 kHz, and a short propagation delay of 22.1 μs. The uniform and reproducible performance of 4H–21DNTT OTFTs show potential for large-area, low-cost real-world applications on industry-compatible bottom-contact substrates.

Conformational Change of Alkyl Chains at Phase Transitions in Thin Films of an Asymmetric Benzothienothiophene Derivative

“…8−10 The flexible alkyl chains generate liquid crystallinity as well as contributing to the high solubility, which is key for fabricating a uniform polycrystalline film without cracks. 16 Iino and co-workers reported that an asymmetric BTBT derivative 2-phenyl-7-decyl [1]benzothieno- [3,2-b] [1]benzothiophene [Ph-BTBT-C 10 (Figure 1a)] forms a molecularly flat surface with very few grain boundaries in a polycrystalline film, when a liquid crystalline film is cooled to its crystallization temperature. 8 The resulting film is subsequently heat-treated to exhibit a high OFET mobility of >10 cm 2 V −1 s −1 .…”

“…This improvement in solubility is particularly important for organic semiconductors, because conjugated molecules with no alkyl chain are often insoluble in most solvents. Many of the recently developed materials for organic field-effect transistors (OFETs), in fact, accompany alkyl side chains on the conjugated backbone, − and they are readily deposited on a solid substrate using solution processes such as spin coating, dip coating, bar coating, blade coating, and inkjet printing techniques, as well as the conventional physical vapor deposition technique.…”

Binary solvent engineering for small-molecular organic semiconductor crystallization

“…24 These high charge carrier mobilities and exceptional stabilities have opened up more pathways for implementing organic semiconductors in the fabrication of high performance semiconductor devices including organic thin film transistors, [25][26][27][28] organic gas sensors, [29][30][31][32][33] organic optoelectronic devices, [34][35][36][37][38][39][40] and complimentary circuits. [41][42][43] Nevertheless, a challenging issue in organic semiconductor growth is the control of crystallization and morphology. This is mainly caused by the intrinsic crystal misorientation when the organic semiconductor is grown in solution, as reported in many small molecular organic semiconductors.…”

Tailoring the molecular weight of polymer additives for organic semiconductors

“…62 Bilgaiyan et al reported the solution shearing of a 6,6 bis( trans -4-butylcyclohexyl)-dinaphtho[2,1- b :2,1- f ]thieno[3,2- b ]thiophene (4H-21DNTT) organic semiconductor based thin film transistor and obtained a mobility of 10.5 cm 2 V −1 s −1 . 63 The 4H-21DNTT based CMOS inverter circuit showed sharp switching behaviors with a 31.5 signal gain. Second, substrate patterning based methods involve the tuning of substrate wettability by using surfactant treatment and/or photolithography patterning, which can effectively confine the deposition of organic semiconductor solutions as well as the subsequent crystal growth and alignment.…”