Electronic systems that use rugged lightweight plastics potentially offer attractive characteristics (low-cost processing, mechanical flexibility, large area coverage, etc.) that are not easily achieved with established silicon technologies. This paper summarizes work that demonstrates many of these characteristics in a realistic system: organic active matrix backplane circuits (256 transistors) for large (Ϸ5 ؋ 5-inch) mechanically flexible sheets of electronic paper, an emerging type of display. The success of this effort relies on new or improved processing techniques and materials for plastic electronics, including methods for (i) rubber stamping (microcontact printing) high-resolution (Ϸ1 m) circuits with low levels of defects and good registration over large areas, (ii) achieving low leakage with thin dielectrics deposited onto surfaces with relief, (iii) constructing highperformance organic transistors with bottom contact geometries, (iv) encapsulating these transistors, (v) depositing, in a repeatable way, organic semiconductors with uniform electrical characteristics over large areas, and (vi) low-temperature (Ϸ100°C) annealing to increase the on͞off ratios of the transistors and to improve the uniformity of their characteristics. The sophistication and flexibility of the patterning procedures, high level of integration on plastic substrates, large area coverage, and good performance of the transistors are all important features of this work. We successfully integrate these circuits with microencapsulated electrophoretic ''inks'' to form sheets of electronic paper.T he backplane circuit consists of a square array of 256 suitably interconnected p-channel transistors. Fig. 1 shows the circuit layout. Fig. 2 presents a cross-sectional illustration of a transistor and a top view of a unit cell. The completed display (total thickness Ϸ1 mm) comprises a transparent frontplane electrode of indium tin oxide (ITO) and a thin unpatterned layer of flexible electronic ''ink'' mounted against a sheet that supports square pixel electrode pads and pinouts; these pixel pads attach, via a conductive adhesive, to the back planes. Each transistor functions as a switch that locally controls the color of the ink, which consists of a layer of polymeric microcapsules filled with a suspension of charged pigments in a colored fluid (1, 2). In each of the four quadrants of the display, transistors in a given column have connected gates, and those in a given row have connected source electrodes. Applying a voltage to a column (gate) and a row (source) electrode turns on the transistor located at the cell where these electrodes intersect. Activating the transistor generates an electric field between the frontplane ITO and the corresponding pixel electrode. This field causes movement of a pigment within the microcapsules, which changes the color of the pixel, as observed through the ITO: when the pigments flow to the ITO side of the capsules, the color of the pigment (white in this case) determines the color of the pixel; when they ...

Considerable advances have been made recently in organic/polymeric electronic materials and devices. [1][2][3][4][5] These materials are useful as active layers in applications such as nonlinear optical devices, 6-8 light-emitting diodes (LED), 9,10 and thin-film field-effect transistors (FETs). [11][12][13][14][15][16][17][18][19][20] We have been studying different materials for thin-film FETs in which the active semiconductor layer consists of organic molecular or polymeric materials. 15,[19][20][21] Organic FETs have potential applications in low-cost large area flexible displays and low-end data storage devices such as smart cards. Organic materials offer numerous advantages for easy processing (e.g., spin-coating, printing, evaporation), good compatibility with a variety of substrates including flexible plastics, and great opportunities in structural modifications. 18,22 Screen printing is a simple and environment-friendly way to produce electronic circuitry and make interconnections. 23 It is a purely additive method in which ink is added where needed. Therefore, patterns can be formed in a single step. With a pitch of printed lines as fine as 250 µm, the printing process can significantly

No abstract

The fabrication and characteristics of organic smart pixels are described. The smart pixel reported in this letter consists of a single organic thin-film field effect transistor (FET) monolithically integrated with an organic light-emitting diode. The FET active material is a regioregular polythiophene. The maximum optical power emitted by the smart pixel is about 300 nW/cm2 corresponding to a luminance of ∼2300 cd/m2.

SynopsisThe dynamic moduli G'(w) and G"(w) for two groups of linear polyethylene fractions (reported mu,/%,, < 1.2) were measured in the melt state using the eccentric rotating disk method. Values of zero shear viscosity 70 were obtained and compared with published results on similar fractions. Molecular weight data were converted to a common basis through intrinsic viscosities in trichlorobenzene (TCB) a t 135OC. With recent data on aW (light scattering) vs.[V]TCB. for linear polyethylene, the relationship a t 19O"C, 70 = 3.40 X 10-14(mu))3.m, was obtained. The flow activation energy E, was 6.4 kcal(7' = 140-195OC). The plateau modulus C$ a t 190°C was determined from the area under the loss modulus peak in one high-molecular-weight sample. The value obtained, G$ = 1.58 X lo7 dyn/cm2, corresponds to an apparent molecular weight between entanglements of 1850. The storage compliance J'(w) becomes anomalously large a t low frequencies. The recoverable compliance J $ could not be determined for any of the fractions.

SynopsisSome results on the melt rheology of hydrogenated polybutadiene (HPB) with narrow-molecular-weight distribution are reported and compared with the corresponding properties of the precursor polybutadienes (PBD) and fractions of linear polyethylene (PE). In linear samples the dynamic moduli obeyed frequency-temperature superposition. The relationship between melt viscosity and intrinsic viscosity at 190°C for HPB was indistinguishable from that for PE, but their flow activation energies were slightly different (E, = 7.2 kcal for HPB and 6.4 kcal for PE). Like PE, but unlike the PBD precursors, the dynamic storage modulus at low frequencies was anomalous. Otherwise, the dynamic moduli of HPB and its PBD precursor were essentially superposable. Plateau moduli from different samples were somewhat variable around an average of GR = 2.31 X lo7 dyn/cm2. The dynamic moduli for the HPB stars, unlike their PBD precursors, did not obey temperature-frequency superposition. At high frequencies the temperature coefficient approached that for linear HPB, but it increased with decreasing frequency, reaching limiting values which depended on the arm length. The flow activation energy ranged from 9 kcal to more than 15 kcal as arm length increased.

SynopsisThree methods for hydrogenating anionically prepared polybutadiene (containing about 8% vinyl double bonds) were investigated: homogeneous catalysis (alkylated transition metal salts), heterogeneous catalysis (nickel on kieselguhr; paladium on calcium carbonate), and stoichiometric reaction with in situ generated diimide. The products were characterized by intrinsic viscosity, gel permeation chromatography, infrared spectroscopy, and melt viscosity. Only the heterogeneous catalysts were found to yield completely hydrogenated products without incorporation of foreign groups and without significant change in the large-scale molecular structure of the chain. The 195OC melt viscosity of linear polybutadiene hydrogenated with heterogeneous catalysts is virtually identical with that of linear polyethylene with the same intrinsic viscosity in trichlorobenzene at 135°C. The solid state properties of hydrogenated polyhutadiene, containing about 20 ethyl branches/1000 main chain atoms, closely resemble those of commercial branched polyethylene.

This letter describes the use of micromolding in capillaries in combination with screen printing to form organic microstructures for applications in microelectronics. Fabrication of plastic transistors with micron feature sizes demonstrates the approach. The performance of these transistors compares favorably with that of similar devices constructed using conventional methods and inorganic substrates, dielectrics, and conductors.