The prospect of using low-temperature processable organic semiconductors to implement transistors, circuits, displays and sensors on arbitrary substrates, such as glass or plastics, offers enormous potential for a wide range of electronic products. Of particular interest are portable devices that can be powered by small batteries or by near-field radio-frequency coupling. The main problem with existing approaches is the large power consumption of conventional organic circuits, which makes battery-powered applications problematic, if not impossible. Here we demonstrate an organic circuit with very low power consumption that uses a self-assembled monolayer gate dielectric and two different air-stable molecular semiconductors (pentacene and hexadecafluorocopperphthalocyanine, F16CuPc). The monolayer dielectric is grown on patterned metal gates at room temperature and is optimized to provide a large gate capacitance and low gate leakage currents. By combining low-voltage p-channel and n-channel organic thin-film transistors in a complementary circuit design, the static currents are reduced to below 100 pA per logic gate. We have fabricated complementary inverters, NAND gates, and ring oscillators that operate with supply voltages between 1.5 and 3 V and have a static power consumption of less than 1 nW per logic gate. These organic circuits are thus well suited for battery-powered systems such as portable display devices and large-surface sensor networks as well as for radio-frequency identification tags with extended operating range.

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We have fabricated pentacene organic thin film transistors with spin-coated polymer gate dielectric layers, including cross-linked polyvinylphenol and a polyvinylphenol-based copolymer, and obtained devices with excellent electrical characteristics, including carrier mobility as large as 3 cm2/V s, subthreshold swing as low as 1.2 V/decade, and on/off current ratio of 105. For comparison, we have also fabricated pentacene transistors using thermally grown silicon dioxide as the gate dielectric and obtained carrier mobilities as large as 1 cm2/V s and subthreshold swing as low as 0.5 V/decade.

Using organic transistors with a floating gate embedded in hybrid dielectrics that comprise a 2-nanometer-thick molecular self-assembled monolayer and a 4-nanometer-thick plasma-grown metal oxide, we have realized nonvolatile memory arrays on flexible plastic substrates. The small thickness of the dielectrics allows very small program and erase voltages (< or = 6 volts) to produce a large, nonvolatile, reversible threshold-voltage shift. The transistors endure more than 1000 program and erase cycles, which is within two orders of magnitude of silicon-based floating-gate transistors widely employed in flash memory. By integrating a flexible array of organic floating-gate transistors with a pressure-sensitive rubber sheet, we have realized a sensor matrix that detects the spatial distribution of applied mechanical pressure and stores the analog sensor input as a two-dimensional image over long periods of time.

Organic thin film transistors (TFTs) are of interest for a variety of large-area electronic applications, such as displays, sensors and electronic barcodes. One of the key problems with existing organic TFTs is their large operating voltage, which often exceeds 20 V. This is due to poor capacitive coupling through relatively thick gate dielectric layers: these dielectrics are usually either inorganic oxides or nitrides, or insulating polymers, and are often thicker than 100 nm to minimize gate leakage currents. Here we demonstrate a manufacturing process for TFTs with a 2.5-nm-thick molecular self-assembled monolayer (SAM) gate dielectric and a high-mobility organic semiconductor (pentacene). These TFTs operate with supply voltages of less than 2 V, yet have gate currents that are lower than those of advanced silicon field-effect transistors with SiO2 dielectrics. These results should therefore increase the prospects of using organic TFTs in low-power applications (such as portable devices). Moreover, molecular SAMs may even be of interest for advanced silicon transistors where the continued reduction in dielectric thickness leads to ever greater gate leakage and power dissipation.

The intrinsic doping level of graphene prepared by mechanical exfoliation and standard lithography procedures on thermally oxidized silicon varies significantly and seems to depend strongly on processing details and the substrate morphology. Moreover, transport properties of such graphene devices suffer from hysteretic behavior under ambient conditions. The hysteresis presumably originates from dipolar adsorbates on the substrate or graphene surface. Here, we demonstrate that it is possible to reliably obtain low intrinsic doping levels and to strongly suppress hysteretic behavior even in ambient air by depositing graphene on top of a thin, hydrophobic self-assembled layer of hexamethyldisilazane (HMDS). The HMDS serves as a reproducible template that prevents the adsorption of dipolar substances. It may also screen the influence of substrate deficiencies.

A major obstacle to the development of organic transistors for large-area sensor, display, and circuit applications is the fundamental compromise between manufacturing efficiency, transistor performance, and power consumption. In the past, improving the manufacturing efficiency through the use of printing techniques has inevitably resulted in significantly lower performance and increased power consumption, while attempts to improve performance or reduce power have led to higher process temperatures and increased manufacturing cost. Here, we lift this fundamental limitation by demonstrating subfemtoliter inkjet printing to define metal contacts with single-micrometer resolution on the surface of high-mobility organic semiconductors to create high-performance p-channel and n-channel transistors and low-power complementary circuits. The transistors employ an ultrathin low-temperature gate dielectric based on a self-assembled monolayer that allows transistors and circuits on rigid and flexible substrates to operate with very low voltages.inkjet printing ͉ organic electronics ͉ self-assembled monolayer T o realize a sustainable society, it is imperative that industrial manufacturing processes undergo a transformation with minimal impact on the environment. From this viewpoint, emerging printable electronics technology (1-6) has attracted considerable attention because it has the potential to drastically reduce ecological footprints and the energy consumed in manufacturing. Moreover, this technology is expected to reduce the material wastage that results from the use of a particular quantity of ink at a certain location.In particular, digital fabrication that employs inkjet technology is expected to play an important role in industrial manufacturing processes because this technique can be applied for patterning high-purity electrically functional materials without preparing original patterning masks (7,8). This application would consequently lead to a reduction in manufacturing costs and/or turnaround time. Inkjet technology has recently proliferated into the area of mass production of color filters for liquid crystal displays (9, 10); this further indicates that this would be the right time for the emergence of printed electronics.However, there still exists a rather wide gap between the resolution required for high-performance electronic devices, such as transistors, and the typical resolution of conventional inkjet printers. For example, microprocessors based on singlecrystal silicon field-effect transistors with a gate length of 32 nm are now in mass production (11), and active-matrix liquidcrystal displays in notebook computers and f lat-screen television sets employ amorphous-silicon thin-film transistors (TFTs) with a channel length of Ϸ2 m. On the other hand, an inkjet print head typically maintains a discharge volume on the order of several picoliters, which creates dots with a minimum diameter of Ϸ30 -50 m on regular paper. The minimum size of a droplet ejected from an inkjet head determines the printing res...

Organic thin film transistors (TFTs) are of interest for lowcost, large-area electronic applications, such as active-matrix displays, electronic paper, flexible microelectronics, and chemical sensors.[1±8] The performance of organic TFTs is determined primarily by the field effect mobility of the charge carriers in the organic semiconductor layer and by the efficiency of injecting and extracting carriers at the source and drain contacts. For virtually all classes of organic semiconductors, the intrinsic carrier mobility depends critically on the degree of molecular ordering and on the extent of the p±p stacking in the material.[9±11] Consequently, optimizing the chemical structure of the organic semiconductor with regard to optimum molecular ordering and maximum orbital overlap continues to be of great importance for the further advancement of organic TFT technology. Despite the extraordinary number of organic semiconductors that have been synthesized and evaluated for use in organic TFTs, [12] the relationships between molecular structure and electrical TFT performance remain sketchy at best. The fused hydrocarbon pentaceneÐby all accounts a rather unspectacular moleculeÐcontinues to deliver the highest electrical performance, regardless of the method of film deposition (thermal evaporation, vapor phase epitaxy, conversion of a solution-processed precursor) and regardless of the contact configuration (top or bottom contacts).[13±15]A useful and practical strategy for investigating the relationships between molecular structure and electrical performance is the systematic variation of the number of repeat units in a particular type of molecular semiconductor. This can be done either by varying the number of units in the conjugated backbone of the molecule, or by varying the length of alkyl substituents. One particularly useful class of model compounds for this type of investigation are the oligothiophenes, due to their relatively straightforward synthesis and because of the wide range of possible modifications in their chemical structure. Organic TFTs based on oligothiophenes were first reported by Horowitz and Garnier [16±18] and later by Dodabalapur, Katz, and others. [19±21] Carrier mobilities reported for a-sexithiophene (a-6T) TFTs have improved from 10 ±4 cm 2 / V s to greater than 0.01 cm 2 /V s.[18±21] Substituting alkyl chains at the a-and a¢-positions of the a-6T molecule led to an increase in carrier mobility to 0.13 cm 2 /V s. [22,23] Carrier mobilities near 0.2 cm 2 /V s have been reported for a-octithiophene (a-8T) TFTs with active layers deposited at 150 C and higher.[24] For many years, oligothiophenes and their alkyl-substituted derivatives have been among the most intensely investigated organic semiconductors and have even led to the demonstration of fast integrated circuits.[3]We have synthesized and evaluated a series of alkyl-substituted oligothiophenes with chromophore length ranging from four to six thiophene units (a,a¢-didecylquaterthiophene, a,a¢-didecylquinquethiophene, and a,a¢-didecy...