Organic Complementary Inverters Research Articles

270 nm ultra-thin self-adhesive conformable and long-term air-stable complimentary organic transistors and amplifiers

Lightweight, flexible, and conformal bioelectronics are essential for wearable technologies. This paper introduces 270 nm thin organic electronics amplifying circuits that are self-adhesive, skin conformal, and long-term air-stable. This report studies the effect of total device thickness, namely 3 μm and 270 nm devices, on the characterization of organic devices before and after buckling, the longevity of organic field-effect transistors (OFETs) over 5 years, and the lamination of OFETs on the human skin. A single-stage organic complementary inverter and a pseudo-complementary amplifier are fabricated to compare their electrical characteristics, with amplification gains of 10 and 64, respectively. Finally, the study demonstrates a five-stage organic complementary inverter can successfully amplify artificial electromyogram and electrocardiogram signals with gains of 1000 and 1088, respectively.

Polymer-Gated Transistors with Only One Solution-Processed, Single Crystalline Organic Microwire for Light and Oxygen Detection.

Organic semiconductors employed in single crystalline form have several advantages over polycrystalline films, such as higher charge carrier mobility and better environmental stability. Herein, we report the fabrication and characterization of a solution-processed microsized single-crystalline organic wire of n-type N,N'-dipentyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C5). The crystal was applied as an active layer in polymer-gated organic field-effect transistors (OFETs) and organic complementary inverter circuits. The single crystaiiline nature of PTCDI-C5 wires were characterized using two-dimensional grazing incidence wide-angle X-ray diffraction (2D-GIXD) and polarized optical microscopy. OFETs with the PTCDI-C5 crystals exhibited high n-type performance and air stability under ambient conditions. To investigate the electrical properties of the single-crystalline PTCDI-C5 wire more precisely, OFETs with only one PTCDI-C5 microwire in the channel were fabricated, and clear n-type characteristics with satisfactory saturation behavior were observed. The device with only one crystal wire exhibited characteristics with significantly lower variation compared to the multicrystal devices, which shows that the density of crystal wires is a critical factor in precisely investigating device performance. The devices exhibited a reversible threshold voltage shift under vacuum and oxygen conditions, without changing the charge carrier mobility. Light-sensitive characteristics were also observed. Additionally, this solution-processed, highly crystalline organic semiconductor can be used in high-performance organic electronic circuits as well as in gas or light sensors.

Photopatterned coumarin‐functionalized polymer dielectric for organic transistors and complementary inverters

AbstractSolution‐processable and patternable polymer dielectrics are of great importance for the development of high‐performance flexible electronic devices, as the patterning process is essential to enhance performance and integration of devices. In this study, we report the photopatterning of a coumarin‐functionalized polymer gate dielectric, poly(7‐(4‐vinyl‐benzyloxyl)‐4‐methylcoumarin) (PVBMC), which was synthesized by introducing the photoreactive coumarin moiety in the position of the hydroxyl group of poly(4‐vinylphenol). Photopatterning of the PVBMC with a resolution of up to 50 μm was performed under ultraviolet light (365 nm) irradiation and the properties of the resulted photopatterned PVBMC were investigated. Pentacene (p‐type) and PTCDI‐C8 (n‐type) organic thin‐film transistors (OTFTs) with the patterned PVBMC were prepared. The resulting p‐ and n‐type OTFTs achieved maximum mobilities of 0.126 cm2/V/s and 1.15 × 10−3 cm2/V/s, respectively, with high operational stability. Organic complementary inverters were also demonstrated by integrating the p‐ and n‐type OTFTs on a single substrate. The resulting devices exhibited a gain (dVOUT/dVIN) of 12.6 and proper switching behavior up to 20 Hz. Our findings demonstrate the potential of this dielectric material for use in other flexible electronic applications.

Wavelength-dependent electrical response of an organic circuit for color sensing without external filters

The use of organic semiconductors in photodetectors has led to promising results in low-cost light sensing. Although the relatively narrow absorption band of most organic compounds limits their use as wide-band photodetectors, the selection of materials with the desired spectral properties permits the fabrication of wavelength-selective sensors without external color filters. Here, we present a polymer-gated organic complementary inverter circuit exhibiting wavelength-dependent output voltage change that enables dual color sensing via the use of organic semiconductors (PTCDI-C5 and pentacene) with distinct absorption spectra. When illuminated, the inverter circuit shows a wavelength (color)-dependent output voltage change due to the difference in the spectral properties of the semiconductors. Compared to the dark state, the output voltage of the circuit increases under long-wavelength and decreases under short-wavelength illumination. These findings demonstrate a novel use of photoresponsive organic semiconductors to construct simple dual-color sensitive sensors which may simplify the fabrication of multi-wavelength detector circuits.

Enhancing Doping Efficiency of Diketopyrrolopyrrole-Copolymers by Introducing Sparse Intramolecular Alkyl Chain Spacing

A synthetic approach that endows high doping efficiency on high-mobility diketopyrrolopyrrole (DPP)-copolymers is described in this paper. Typical DPP-copolymers are not suitable for molecular doping, which relies on intermolecular charge transfer, presumably because of their relatively high ionization potential or weak intermolecular charge transfer characteristics between the dopant and acceptor of copolymers. Herein, we introduce new DPP-copolymers with strategically designed sparse intramolecular alkyl chain spacing where dopant molecules can reside. The resulting two type A1-D1-A2-D1 and A1-D2-A2-D2 terpolymers consist of cyclopentadithiophenes or cyclopentadithiophenyl thiophene as alternative donors, diketopyrrolopyrrole as an acceptor, and difluorinated benzothiadiazole as another acceptor. These new DPP-copolymers have significantly enhanced doping efficiency compared to conventional DPP-copolymers, exhibiting typical features of integer charge transfer, as confirmed by ultraviolet-visible-near-infrared absorption spectroscopy, electron paramagnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and thin film conductivity analyses. Moreover, doping-induced solubility control, which is not possible with other conventional DPP-copolymers due to low doping efficiency, is applicable, thus resulting in arrays of high-mobility organic field-effect transistors and complementary all-polymer inverters. This study sheds light on the possibility of tuning the doping efficiency of donor-acceptor copolymers without sacrificing their intrinsic properties, such as their well-ordered molecular packing and high charge carrier mobility.

Wafer‐Scale Organic Complementary Inverters Fabricated with Self‐Assembled Monolayer Field‐Effect Transistors

AbstractSelf‐assembled monolayers (SAMs) of π‐conjugated molecules can achieve robust charge transport by the formation of ordered 2D layers at the desired regions, which enable their application for organic integrated circuits. Here, the self‐assembled monolayer field‐effect transistor concept is applied as a scalable method to realize fully integrated complementary inverters by stepwise semiconductor deposition. Two‐component stacked bilayer ambipolar transistors are fabricated by semiconducting self‐assembled monolayers (n‐SAM or p‐SAM) as the bottom layer and a complementary thin‐film semiconductor layer on top. The integrated complementary metal‐oxide‐semiconductor like (CMOS‐like) inverter achieves proper logic performances. The nanometer‐thin monolayers exhibit effective charge transport and their flat, homogeneous surfaces benefit the interconnected growth of the top layer. Furthermore, by controlling the solution‐based and region‐selective deposition of p‐ and n‐type SAMs, fully integrated CMOS inverters are realized on wafer scale by photolithography for the first time. The CMOS inverters show a nearly 100% yield with a gain up to 48, and noise margin 3.68 V (73.6% of VDD/2). The strategy of semiconducting SAMs for digital logic gates demonstrates a reliable approach for sophisticated large‐area circuits.

Direct Printing of Asymmetric Electrodes for Improving Charge Injection/Extraction in Organic Electronics.

Engineering the energy levels of organic conducting materials can be useful for developing high-performance organic field-effect transistors (OFETs), whose electrodes must be well controlled to facilitate easy charge carrier transport from the source to drain through an active channel. However, symmetric source and drain electrodes that have the same energy levels are inevitably unfavorable for either charge injection or charge extraction. In this study, asymmetric source and drain electrodes are simply prepared using the electrohydrodynamic (EHD)-jet printing technique after the careful work function engineering of organic conducting material composites. Two types of additives effectively tune the energy levels of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate-based composites. These solutions are alternately patterned using the EHD-jet printing process, where the use of an electric field makes fine jet control that enables to directly print asymmetric electrodes. The asymmetric combination of EHD-printed electrodes helps in obtaining advanced charge transport properties in p-type and n-type OFETs, as well as their organic complementary inverters. This strategy is believed to provide useful guidelines for the facile patterning of asymmetric electrodes, enabling the desirable properties of charge injection and extraction to be achieved in organic electronic devices.

Unexpected Benefits of Contact Resistance in 3D Organic Complementary Inverters

AbstractContact resistance has long been a major problem in organic transistors. The potential advantages of having such a resistance in novel organic field‐effect complementary inverters are demonstrated by means of finite‐element simulation. A systematic introduction of the charge‐injection barrier leads to a remarkable enhancement in the voltage transfer curve. Quantitatively, the maximum gain increases from 8.9 to 50 by increasing the barrier from 0 to 0.5 eV, at a dielectric thickness of 600 nm and a supply voltage of 5 V. This observation is elucidated by the fundamental transistor parameters and by the carrier distribution inside the semiconductors. These results suggest that the established paradigm of device engineering may have to be reconsidered when designing specific circuit applications.

Compact modelling and SPICE simulation for three-dimensional, inkjet-printed organic transistors, inverters and ring oscillators

We report an in-depth study of three-dimensional (3D) inkjet-printed flexible organic field-effect transistors (FETs) and integrated circuits (ICs), and demonstrate the necessity, the feasibility and the key aspects of modelling-driven design and analysis. In particular, we performed compact modelling of the flexible printed organic FETs to determine transistor parameters from measured electrical characteristics, and to optimize the design of transistors for a balanced inverter. We also conducted a SPICE simulation of both static and dynamic behaviours of flexible printed organic complementary inverters and ring oscillators. This study revealed design rules to guide fabrication of the 3D structure of the inverter. The study also showed that the parasitic capacitances are dominant factors that determine the transient behaviour of the ring oscillator. Our work provides insights that can guide further improvement of flexible printed organic FETs and ICs towards the realisation of increasingly complex organic ICs and unconventional electronic applications.

Intense-pulsed-UV-converted perhydropolysilazane gate dielectrics for organic field-effect transistors and logic gates.

We fabricated a high-quality perhydropolysilazane (PHPS)-derived SiO2 film by intense pulsed UV irradiation and applied it as a gate dielectric layer in high-performance organic field-effect transistors (OFETs) and complementary inverters. The conversion process of PHPS to SiO2 was optimized by varying the number of intense pulses and applied voltage. The chemical structure and gate dielectric properties of the PHPS-derived SiO2 films were systematically investigated via Fourier transform infrared spectroscopy and leakage current measurements, respectively. The resulting PHPS-derived SiO2 gate dielectric layer showed a dielectric constant of 3.8 at 1 MHz and a leakage current density of 9.7 × 10−12 A cm−2 at 4.0 MV cm−1. The PHPS-derived SiO2 film was utilized as a gate dielectric for fabricating benchmark p- and n-channel OFETs based on pentacene and N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8), respectively. The resulting OFETs exhibited good electrical properties, such as carrier mobilities of 0.16 (±0.01) cm2 V−1 s−1 (for the pentacene OFET) and 0.02 (±0.01) cm2 V−1 s−1 (for the PTCDI-C8 OFET) and an on–off current ratio larger than 105. The fabrication of the PHPS-derived SiO2 gate dielectric layer by a simple solution process and intense pulsed UV irradiation at room temperature serves as a novel approach for the realization of large-area flexible electronics in the flexible device industry of the future.

Acceptor Unit Effects for Ambipolar Organic Field-Effect Transistors Based on TIPS-Benzodithiophene Copolymers

Two narrow band gap triisopropylsilyl substituted benzo[1,2-b:4,5-b] dithiophene (TIPS-BDT) derivatives, P1 (1.65 eV) and P2 (1.46 eV) are synthesized for ambipolar organic field-effect transistors and complementary inverters. Two electron acceptor units, heptadecanyl substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) and ethylhexyl substituted diketopyrrolo[3,4-c]pyrrole (DPP) are incorporated to tune the structure and resulting properties of the donor-acceptor type copolymers. Structural modification based on the acceptor unit variation, resulted in comparable electrochemical, optical, microstructural, and charge transporting properties, as well as environmental and operational stability. TIPS-BDT copolymers with TPD acceptor units show comparatively superior performance, with field effect mobility ∼10-3 cm2V-1s-1 for both holes and electrons and inverter gain ∼18 with poly(methyl methacrylate) gate dielectric.

Printed Organic Complementary Inverter with Single SAM Process Using a p-type D-A Polymer Semiconductor

The demonstration of the complementary integrated circuit using printing processes is indispensable for realizing electronic devices using organic thin film transistors. Although complementary integrated circuits have advantages such as low power consumption and a wide output voltage range, complementary integrated circuits fabricated by the printing method have problems regarding driving voltage and performance. Studies on fabrication processes of electronic circuits for printing technology, including optimization and simplification, are also important research topics. In this study, the fabrication process of the printed complementary integrated circuit was simplified by applying a p-type donor-acceptor (D-A) polymer semiconductor, which is not strongly affected by the electrode work function. An inverter circuit and the ring oscillator circuit were demonstrated using this process. The fabricated ring oscillator array showed excellent performance, with low voltage operation and low performance variation.

Effects of interfacial tension and molecular dipole moment on the electrical characteristics of low-voltage-driven organic electronic devices

In organic electronic/photonic devices, numerous types of interfaces and their properties exhibit profound correlation with device performance. For optimizing the performance of organic electronic/photonic devices, appropriate and effective interface engineering needs to be developed. In this study, a high dielectric constant material, hafnium dioxide (HfO2), and an organic semiconductor, N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13) were adopted as the dielectric and active layers, respectively, to fabricate low-voltage-driven organic thin-film transistors. Three kinds of insulating polymers were selected to serve as buffer layers (BLs) to modify HfO2. After the addition of BLs onto HfO2, the insulating properties of HfO2 and the microstructures of PTCDI-C13 active layers improved, resulting in considerably enhanced electrical characteristics and stability of the devices. Among different polymeric BLs, the BL polymer exhibiting smaller interfacial tension with PTCDI-C13 can induce PTCDI-C13 to form better microstructures and generate lower interfacial trap density despite the rougher topography of polymeric BL, leading to improved electrical characteristics of the corresponding device. However, we observed that BL polymer with larger dipole moment of side groups can yield better electrical stability of the corresponding device under continuous operation compared with polymers with smaller interfacial tension. During long-term operation, the dipoles can be aligned by an electric field and form a strong dipole layer to facilitate charge accumulation and alleviate device degradation caused by bias-stress-induced trap/defect states. We further adopted a BL polymer with both small interfacial tension and large dipole moment to fabricate low-voltage-driven organic complementary inverters. The inverter can exhibit high electrical characteristics and stability during continuous operation. Interfacial tension and molecular dipole moment are possible important issues for effective interface engineering.

Organic Complementary Inverter Circuits Fabricated with Reverse Offset Printing

Abstractp‐Type and n‐type organic thin film transistors (OTFTs) and complementary inverter circuits with finely patterned electrodes are fabricated by reverse offset printing. The electrodes achieve a channel length of less than 3 µm under optimized printing conditions. High‐performance OTFTs are fabricated using these electrodes and printed p‐type and n‐type organic semiconductors, each achieving a mobility of 0.2 cm2 V−1 s−1 at a channel length of 50 µm. A complementary inverter circuit fabricated with a stacked OTFT structure is demonstrated using reverse offset printing. The inverter circuits successfully operate at a supply voltage as low as 2.5 V with a high signal gain of 14. These results are expected to contribute greatly to the development of integrated circuits with high‐speed operation using OTFTs.

Systematic optimization of MWCNT-PEDOT:PSS composite electrodes for organic transistors and dye-sensitized solar cells: Effects of MWCNT diameter and purity

Abstract Multi-walled carbon nanotubes (MWCNTs) and polymer composites have attracted significant attention as metal-free electrode materials for various electronic devices. Many studies have presented strategies to enhance the electrical conductivity of MWCNT/polymer composites. However, systematic studies on the effects of MWCNT features on the composite properties are still missing. Such studies can further the development of MWCNT/polymer-based conducting materials. Herein, we characterize composite films of MWCNTs and poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS), with variations in the MWCNT diameter and purity. MWCNT features greatly affect the physical/chemical/electrical properties of the MWCNT/PEDOT:PSS composite films. In addition, the diameter and purity of MWCNTs also influenced the transition behavior of the composite films during the hydrochloric acid-methanol treatment, which was performed for increasing electrical conductivity. As a result, we could optimize the performance of organic transistors and dye-sensitized solar cells (DSSCs) using MWCNT/PEDOT:PSS composite films as source/drain electrodes and catalytic counter electrodes, respectively. Furthermore, using the optimized device parameters, we successfully fabricated high performance fluorine doped tin oxide-free DSSCs and high-gain organic complementary inverters using MWCNT/PEDOT:PSS composite electrodes.

Flexible Low-Power Organic Complementary Inverter Based on Low- ${k}$ Polymer Dielectric

Organic complementary inverters that have high performance, low-power operation, and flexible compatibility are achieved using a simple and low-cost method to prepare a thin low- ${k}$ polymer dielectric on sputtered C nanoparticles. The operation voltage of the flexible inverter can be as low as 3 V, and the gain is close to 200, which is superior to most reported organic-based inverters. The flexible inverter also exhibits outstanding switching stability in multiple signal processing. The present organic inverters may be of value in portable and wearable electronics.

Charge-transfer complex modified bottom electrodes for high performance low voltage organic field-effect transistors and circuits

Abstract By using charge transfer complex silver and 2,3-dichloro-5,6-dicyano-p-benzoquinone (AgDDQ) modified silver as the bottom contact source/drain electrodes, high performance organic transistors and complementary inverter circuits using dinaphtho[2,3-b:2′,3’-f]thieno[3,2-b]thiophene (DNTT) as P-type organic semiconductors and N,N’-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2) as N-type organic semiconductors were demonstrated. Devices with Ag-DDQ bottom contact electrodes exhibit good compatibility for both P and N-type organic semiconductors, the transistors and inverters exhibit excellent stability after storing in air ambient for more than 40 days. The fabrication process is compatible with photolithography technology, which is applicable for large area integrated circuits. All these results indicate the potential application of Ag-DDQ modified electrodes in all-organic, flexible, and low-power electronics.

Benzothiadiazole-Based Small-Molecule Semiconductors for Organic Thin-Film Transistors and Complementary-like Inverters.

New benzothiadiazole derivatives, 4,7-bis(5-phenylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (PT-BTD) and 4,7-bis[4-(thiophen-2-yl)phenyl]benzo[c][1,2,5]thiadiazole (TP-BTD), were synthesized and characterized as small-molecule organic semiconductors for organic thin-film transistors (OTFTs) and complementary inverters. The thermal, optical, and electrochemical properties of the new compounds were fully characterized. Vacuum-deposition and solution-shearing methods were used to fabricate thin films based on these compounds. Thin films based on PT-BTD exhibited p-channel characteristics with hole mobilities as high as 0.10 cm2 V-1 s-1 and current on/off ratios >107 for top-contact/bottom-gate OTFT devices. With an optimized blending ratio of PT-BTD and the representative n-channel semiconductor N,N'-1H,1H-perfluorobutyl dicyanoperylenediimide, bulk heterojunction ambipolar transistors were fabricated with balanced hole and electron mobilities of 0.10 and 0.07 cm2 V-1 s-1 , respectively. Furthermore, a complementary-like inverter was fabricated using ambipolar thin-film transistors, which showed a high voltage gain of 84.

Kilohertz organic complementary inverters driven by surface-grafting conducting polypyrrole electrodes

Surface-grafting conducting polymer has advantage to circumvent the difficulty in patterning as well as the weak interface adhesion on substrate of the conventional conducting polymer, which would be desirable for its application as electrodes in electronic devices. In this work, the patterned surface-grafting polypyrrole (PPY) is used as electrode, which shows merits such as strong interface adhesion, robustness against solvent treatment, easy scaling-up, and good conductivity. Remarkably, the surface-grafting PPY electrodes can efficiently drive both p-type and n-type organic field-effect transistors. By combining p-/n-type transistors, organic complementary inverters are constructed with PPY electrodes, which exhibit low operational voltage (<8V), high gain (6–17), and low power dissipation (several tens of nW). The switching voltage is approximately 0.5Vdd with a high noise margin (>70% of 0.5Vdd). Dynamic switching measurements indicate that the inverter has an operational frequency of about 3.3kHz. This is the first report on kilohertz organic complementary inverter driven with surface-grafting conducting polymer electrodes. High device performance, together with the facile patternability and other merits, may promote the application of surface-grafting conducting polymer electrode in the field of organic electronics.

Flexible ambipolar organic field-effect transistors with reverse-offset-printed silver electrodes for a complementary inverter

We report ambipolar organic field-effect transistors and complementary inverter circuits with reverse-offset-printed (ROP) Ag electrodes fabricated on a flexible substrate. A diketopyrrolopyrrole-based co-polymer (PDPP-TAT) was used as the semiconductor and poly(methyl methacrylate) was used as the gate insulator. Considerable improvement is observed in the n-channel electrical characteristics by inserting a cesium carbonate (Cs2CO3) as the electron-injection/hole-blocking layer at the interface between the semiconductors and the electrodes. The saturation mobility values are 0.35 cm2 V−1 s−1 for the p-channel and 0.027 cm2 V−1 s−1 for the n-channel. A complementary inverter is demonstrated based on the ROP process, and it is selectively controlled by the insertion of Cs2CO3 onto the n-channel region via thermal evaporation. Moreover, the devices show stable operation during the mechanical bending test using tensile strains ranging from 0.05% to 0.5%. The results confirm that these devices have great potential for use in flexible and inexpensive integrated circuits over a large area.