Venkataram Reddy Raju

Paper-like electronic displays: Large-area rubber-stamped plastic sheets of electronics and microencapsulated electrophoretic inks

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 (≈5 × 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 (≈1 μm) 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 high-performance 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 (≈100°C) annealing to increase the on/off 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.

Organic smart pixels

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.

Nonphotolithographic fabrication of organic transistors with micron feature sizes

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.

ORGANIC COMPLEMENTARY RING OSCILLATORS

We report the characteristics of complementary organic ring oscillators. The shortest delay time measured is 38 μs per stage that corresponds to a 2.63 kHz oscillation frequency. The active material in the n-channel transistors is copper hexadecafluorophthalocyanine and that in the p-channel transistors is an oligothiophene/oligothiophene derivative.

Polymer light emitting diodes: new materials and devices

Abstract Single layer polymer light emitting diodes (LEDs) are ideal candidates for practical applications due to their easy processing conditions. However, low quantum efficiency of light generation is often obtained due to imbalanced charge injection and transport of holes and electrons. In this paper we report new conjugated polymers with electron deficient oxadiazole moieties as side-chains. These polymers have shown at least an order of magnitude increase in electroluminescence efficiencies and better charge injection properties compared to their corresponding conjugated backbone polymers. In addition, novel patterned LED device structures which emit in geometries with features into the sub-micron range will be presented. Finally, issues regarding integration of polymer transistors with organic LEDs will be discussed.

Rubber stamped plastic circuits for electronic paper

This paper illustrates the use of a high resolution form of rubber stamping, known as microcontact printing (/spl mu/CP), for patterning plastic active matrix drive circuitry designed for electronic paper. The high resolution (/spl sim/1 /spl mu/m) of the printed elements, the large area coverage (/spl sim/1 sq ft.) and the good electrical performance of these systems suggest that the methods, materials and processing sequences may be attractive for realistic applications of plastic electronics.

Large Area, Rubber Stamped Plastic Circuits for Electronic Paper

This paper illustrates the use of a high resolution form of rubber stamping, known as microcontact printing (μCP), for patterning plastic active matrix drive circuitry designed for electronic paper. The high resolution (∼1 [.mu]m) of the printed elements, the large area coverage (∼1 sq. ft.) and the good electrical performance of these systems suggest that the methods, materials and processing sequences may be attractive for realistic applications of plastic electronics.