Myeong Jin Kang

Patternable Solution‐Crystallized Organic Transistors with High Charge Carrier Mobility

Development of high-performance printed semiconductor devices is highly desired with the expectation for the nextgeneration technologies of “printable electronics” providing simply fabricated, fl exible, large-area, low-cost, and environmentally friendly electronic products such as paper-like fl exible displays. Patterned arrays of printed organic fi eld-effect transistors (OFETs) based on chemically stable solutionprocessed organic semiconductors are regarded as key devices that operate as fundamental switching components in, for example, pixel-controlling active-matrix elements. However, performance of conventional solution-coated noncrystal organic thin-fi lm transistors has yet to be improved for practical use in general electronic circuitry. Here, newly developed arrays of patterned crystalline OFETs of air-stable compound 2,9-didecyl-dinaphtho[2,3-b:2’,3’-f ]thieno[3,2-b]thiophene (C 10 -DNTT) formed from hot solution are presented. A method of oriented growth is introduced to provide the singlecrystalline fi lms of C 10 -DNTT that regulates the crystallizing direction and positions in a single process. The benchmark value, 10 cm 2 V − 1 s − 1 , of the charge mobility is achieved for the present OFETs, far exceeding the performance of former devices and opening a practical way to realize printed and fl exible electronics with suffi cient switching speed. The result is attributed to almost perfect molecular periodicity in the crystal fi lms, which allows effective intermolecular charge transport of the electrons.

Alkylated Dinaphtho[2,3‐b:2′,3′‐f]Thieno[3,2‐b]Thiophenes (Cn‐DNTTs): Organic Semiconductors for High‐Performance Thin‐Film Transistors

Organic thin-fi lm transistors (OTFTs) have attracted great interest for their potential use in several electronic applications, including active-matrix displays, electronic paper, and chemical sensors. [ 1 ] Among the many semiconducting materials evaluated in the TFT confi guration, pentacene is the best as it shows the highest fi eld-effect mobility ( > 3.0 cm 2 V − 1 s − 1 ). [ 2 , 3 ] On the other hand, new organic semiconductors are being actively investigated to further improve the performance of OTFTs. In fact, superior unconventional organic semiconductors used to produce high-performance OTFTs have been recently reported, including picene (3.2 cm 2 V − 1 s − 1 ), [ 4 ] trans -1,2-dithieno[2,3b ′ :3,2d ′ ]thiophene ethene (DTTE, 2.0 cm 2 V − 1 s − 1 ), [ 5 ] dithieno[2,3d ;2 ′ ,3 ′ d ′ ]benzo[1,2b ;4,5b ′ ]dithiophene (DTBDT, 1.7 cm 2 V − 1

Flexible low-voltage organic thin-film transistors and circuits based on C10-DNTT

Using the recently developed organic semiconductor, 2,9-didecyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C10-DNTT), we have fabricated organic thin-film transistors and ring oscillators on flexible polymeric substrates. By utilizing a gate dielectric with a small thickness (5.3 nm) and a large capacitance (800 nF cm−2), the transistors can be operated with relatively low voltages of about 2 to 3 V. To improve the charge exchange between the organic semiconductor and the gold source and drain contacts, a thin layer of a non-alkylated organic semiconductor (DNTT) sandwiched between two thin layers of a strong organic dopant (NDP-9) was inserted between the C10-DNTT and the gold contacts. The optimized transistors have a field-effect mobility of 4.3 cm2 V−1 s−1, an on/off current ratio of 108, and a subthreshold swing of 68 mV per decade. The ring oscillators have a signal propagation delay of 5 μs per stage at a supply voltage of 3 V, making these the fastest organic circuits at supply voltages below 7 V reported to date.

Flexible Low‐Voltage Organic Complementary Circuits: Finding the Optimum Combination of Semiconductors and Monolayer Gate Dielectrics

Low-voltage p-channel and n-channel organic transistors with channel lengths down to 0.5 μm using four small-molecule semiconductors and ultra-thin dielectrics based on two different phosphonic acid monolayers are fabricated on plastic substrates and studied in terms of effective mobility, intrinsic mobility and contact resistance. For the optimum materials combination, flexible complementary circuits have signal delays of 3.1 μs at 5 V.

Unique three-dimensional (3D) molecular array in dimethyl-DNTT crystals: a new approach to 3D organic semiconductors

Two isomeric dimethyl derivatives of dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (2,9- and 3,10-DMDNTT) were synthesized and characterized. Their crystal structures were classified as unique three-dimensional (3D) herringbone arrangements. Of them, 3,10-DMDNTT preserves the same packing structure in the thin-film phase, and the film acted as a superior semiconductor channel in field-effect transistors with mobility up to 0.8 cm2 V−1 S−1.

High-performance organic transistors with high-k dielectrics: A comparative study on solution-processed single crystals and vacuum-deposited polycrystalline films of 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene

High carrier-mobility organic field-effect transistors are developed employing high-k gate dielectrics so that unprecedentedly high transconductance is realized. 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C10-DNTT) solution-crystallized films are coated on hybrid gate insulators of silane self-assembled monolayers and high-k Al2O3 formed by atomic-layer-deposition. Intrinsically high carrier mobility exceeding 10 cm2/Vs in the crystalline C10-DNTT is preserved even on the high-k gate insulators because of suppressed coupling of the field-induced carriers to the polarization of the dielectrics.

Split-gate organic field-effect transistors for high-speed operation.

Split-gate organic field-effect transistors have been developed for high-speed operation. Owing to the combination of reduced contact resistance and minimized parasitic capacitance, the devices have fast switching characteristics. The cutoff frequencies for the vacuum-evaporated devices and the solution-processed devices are 20 and 10 MHz, respectively. A speed of 10 MHz is the fastest device reported so far among solution-processed organic transistors.

A comprehensive study of charge trapping in organic field-effect devices with promising semiconductors and different contact metals by displacement current measurements

A systematic and comprehensive study on the charge-carrier injection and trapping behavior was performed using displacement current measurements in long-channel capacitors based on four promising small-molecule organic semiconductors (pentacene, DNTT, C10-DNTT and DPh-DNTT). In thin-film transistors, these semiconductors showed charge-carrier mobilities ranging from 1.0 to 7.8 cm2 V−1 s−1. The number of charges injected into and extracted from the semiconductor and the density of charges trapped in the device during each measurement were calculated from the displacement current characteristics and it was found that the density of trapped charges is very similar in all devices and of the order 1012 cm−2, despite the fact that the four semiconductors show significantly different charge-carrier mobilities. The choice of the contact metal (Au, Ag, Cu, Pd) was also found to have no significant effect on the trapping behavior.

Performance and stability of flexible low-voltage organic thin-film transistors based on C 10 -DNTT

Using the recently developed organic semiconductor C10-DNTT and a thin, high-capacitance gate dielectric we have fabricated flexible organic thin-film transistors that combine a field-effect mobility of 4.3 cm2/Vs, an on/off ratio of 108, and a subthreshold swing of 68 mV/decade. To improve the charge exchange between the organic semiconductor layer and the metal source and drain contacts, a thin layer of a non-alkylated organic semiconductor (DNTT) sandwiched between two thin layers of a strong organic dopant (NDP-9) were inserted between the C10-DNTT and the metal contacts. Flexible ring oscillators have a signal propagation delay of 5 μsec per stage at a supply voltage of 3 V.