Organic thin-film transistors (OTFTs) have received significant consideration in recent years for potential deployment in low-cost and large-area printed electronics. D-type flip-flop (D-FF) circuits are one of the most important logic gates for data processing and storage in such applications. Previous work has reported on NAND-based organic D-FF circuits. Although the demonstrated printed circuits exhibit low voltage operation at 10 V, each D-FF circuit requires 34 TFT devices and occupies an area of 192 mm2 per D-FF circuit. This paper demonstrates inkjet-printed organic D-FF circuits with a compact circuit design using clocked inverters and transmission gates and compares the occupied area and the circuit performance with those of NAND-based organic D-FF circuits. The compact organic D-FF circuits require only 18 OTFT devices, and can use 60% less area than NAND-based organic D-FF circuits fabricated by the same process. In addition, the compact organic D-FF circuits exhibit a shorter propagation delay time than the NAND-based D-FF circuits. The mechanism for the shortened delay time will be discussed in detail, based on SPICE simulations. These results demonstrate the high potential of these compact organic D-FF circuits in printable electronics.

Low-voltage circuit operation is one of the primary requirements for the practical use of printed electronic devices employing organic thin-film transistors, in particular, the driving of devices with power supplied by energy harvesting using organic solar cells or biofuel cells, which require low-voltage operation, typically below 1 V. This study reports on printed organic inverter circuits that operate at 0.3 V with negligible hysteresis, a gain of greater than 10, and rail-to-rail input and output operation, by utilizing a blend of 2,7-dihexyl-dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene and polystyrene. The ultralow voltage operation of these circuits can be attributed to its finely tunable turn-on voltage, low trap density, ohmic contacts, and minimal channel length modulation coefficients. Moreover, these organic inverter circuit arrays exhibit high uniformity with an average switching voltage of 0.32 ± 0.03 V. As a result, printed organic devices with ultralow operating voltages can be realized with exceptional reproducibility, helping to further the potential of printed electronic applications based on ultralow power organic devices in the future Internet of Things (IoT) ecosystem.

In this paper, we demonstrate three-dimensional (3D) integrated circuits (ICs) based on a 3D complementary organic field-effect transistor (3D-COFET). The transistor-on-transistor structure was achieved by vertically stacking a p-type OFET over an n-type OFET with a shared gate joining the two transistors, effectively halving the footprint of printed transistors. All the functional layers including organic semiconductors, source/drain/gate electrodes, and interconnection paths were fully inkjet-printed except a parylene dielectric which was deposited by chemical vapor deposition. An array of printed 3D-COFETs and their inverter logic gates comprising over 100 transistors showed 100% yield, and the uniformity and long-term stability of the device were also investigated. A full-adder circuit, the most basic computing unit, has been successfully demonstrated using nine NAND gates based on the 3D structure. The present study fulfills the essential requirements for the fabrication of organic printed complex ICs (increased transistor density, 100% yield, high uniformity, and long-term stability), and the findings can be applied to realize more complex digital/analogue ICs and intelligent devices.Keywords: 3D circuit; complementary organic field-effect transistor; full adder; inkjet printing; printed integrated circuit

There have been only a limited number of reports on solution-processed n-channel organic thin-film transistor (OTFT) devices with high levels of electrical performance because the material design process for n-type organic semiconductors is relatively difficult compared with p-type semiconductors, and further chemical modification of the functional groups is required. As a result, the development of soluble n-type organic semiconductors with high carrier mobilities has remained a challenge. Our work addresses this by introducing a novel molecular design to realize soluble n-type organic semiconductors with high electron mobilities through the simple substitution of trifluoromethyl or trifluoromethoxy groups at the meta positions to support sufficient solubility, creating suitable LUMO energy levels and high crystallinity. These newly designed benzobis(thiadiazole) (BBT)-based molecules showed electron mobilities as high as 0.61 cm2 V–1 s–1 in solution-processed OTFT devices. As a practical application in printed electronics, we demonstrated an organic complementary inverter circuit with OTFT devices using the developed soluble organic semiconductors. Because of their high solubility level and superior electrical properties compared with common para-substituted derivatives, the utilization of meta substituents is a new strategy for the design of soluble organic semiconductors in the field of OTFT device fabrication.

We report on the cross-sectional profile control of printed electrodes fabricated from silver nanoparticle inks with water-based solvents by inkjet printing. Systematically varying the ambient conditions and time for the drying process corresponded to changes in electrode shape. In general, lower humidity levels resulted in concave electrode profiles due to the coffee-ring effect, while higher humidity levels resulted in convex profiles. Printed capacitors with trapezoidal-shaped lower electrodes showed much better electrical breakdown strength than those with concave-shaped lower electrodes. Solution-processed organic thin-film transistors with trapezoidal gate electrodes operated reproducibly and exhibited good electrical characteristics with very low gate-leakage currents. The methods can be utilized in the fabrication of printed electronic devices with stacked layers, such as thin-film capacitors and transistors.Keywords: humidity; inkjet printing; organic thin-film transistors; printed electronics; profile control; silver nanoparticle ink;

Novel semiconducting polymers consisting of thiophene and anthracene units without alkyl groups were successfully synthesized through soluble precursor polymers and applied to the organic thin-film transistors (OTFTs). Thermal elimination of leaving groups from the precursor polymers by retro Diels–Alder reaction was proved by thermogravimetric analysis (TGA), FT-IR, and UV–vis spectroscopy. The resulting films of the semiconducting polymers showed good surface morphologies even after thermal elimination, resulting in good semiconducting behavior with mobility of 0.015 cm2 V–1 s–1 in the typical top-contact OTFT. In addition, the devices based on these polymers are stable under ambient conditions and maintained good transistor performance even after being stored in air for 2 months.

•We fabricated organic TFTs and pseudo-CMOS inverter using full solution-processing.•Patterning conditions for the silver nanoparticle inks are optimized.•NAND and NOR circuits based on the pseudo-CMOS circuits that are demonstrated.•Fabricated circuits exhibited good characteristics at a low supply voltage.•Low temperature processing below 150 °C.We have demonstrated fully solution-processed inverter, NAND and NOR circuits using pseudo-CMOS logic and p-type organic TFT devices with printed electrodes that were fabricated using ink-jet printed silver nanoparticle inks at low temperatures. In order to optimize the gate electrode profiles, we thoroughly assessed the surface wettability of the silver nanoparticle inks. The pseudo-CMOS inverter circuit exhibited exceptional switching characteristics with a high signal gain of 34 at a supply voltage of 20 V. The NAND and NOR circuits also exhibited excellent logic characteristics, whereby the switching voltage was approximately VDD/2 with a high noise margin and short delay time of 12.5 ms.

Isomerically pure syn-/anti-isomers of 2,8-dimethylanthradithiophene (DMADT) were synthesized in five steps and characterized using thermogravimetry, X-ray single crystal analysis, UV–vis absorption, and electrochemical measurements. The physical properties in solution were slightly different for each isomer, whereby the more obvious differences were observed in the solid state. A field-effect transistor using the anti-isomer showed a much higher performance than that using the syn-isomer.