Integrated Complementary-Like Circuits Based on Organic Ambipolar Transistors
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I11.9.1
Integrated Complementary-Like Circuits Based on Organic Ambipolar Transistors *
Thomas D. Anthopoulos1 , Dago M. de Leeuw1, Sepas Setayesh1, Eugenio Cantatore1 Cristina Tanase2, Paul W. M. Blom2 and Jan C. Hummelen2 1
Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands
2
Molecular Electronics, Materials Science CentrePlus, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
ABSTRACT We report on an approach towards integrated complementary-like circuits based on organic ambipolar transistors. In particular, we show that ambipolar transport can be achieved within a single transistor channel using gold electrodes and a solution processable polymer-small molecule blend as the electroactive material. To demonstrate the suitability of these devices for practical utilisation in logic circuits we realise complementary-like voltage inverters comprised entirely of ambipolar transistors. Moreover, by integrating several such inverters we are able to demonstrate more complex circuits such as ring oscillators. INTRODUCTION As the complexity of organic integrated circuits increases there is an increasing need for higher yield, better noise immunity and lower power dissipation [1]. One route that meets all these requirements is the use of complementary transistor circuitry [2]. Despite the advantages, however, state-of-the-art organic complementary circuits are prepared by thermal evaporation of a p- and an n-type semiconductor through a shadow mask [2], thus making device fabrication difficult and potentially expensive. A much simpler approach towards organic complementary circuits was recently demonstrated and is based on ambipolar organic field-effect transistors (OFETs) [3]. Ambipolar transistors can function either as p- or n-channel devices depending upon the biasing conditions. Although, inorganic ambipolar transistors are known for more than two decades [4], their organic counterparts have become reality only in recent years [3, 5-7]. Making use of this peculiar device property, the Philips group was the first to demonstrate a complementary-like inverter employing two identical ambipolar transistors based on organic polymer-small molecule interpenetrating networks as well as low bandgap molecular semiconductors [3, 7-9]. Here we report on organic ambipolar transistors based on polymer-small molecule interpenetrating networks. We show that by integrating a number of such devices, fabrication of complementary-like logic circuits is possible. In particular, we demonstrate the dynamic characteristics of inverters and multi-stage ring oscillators comprised entirely of ambipolar transistors.
I11.9.2
EXPERIMENTAL DETAILS Discrete transistors were fabricated using heavily doped p-type Si wafers as the back gate electrode with a 200 nm thermally oxidized SiO2 layer as the gate dielectric. Using conventional photolithography, gold source and drain electrodes were defined with channel length and width in the range1.5-40 µm and 1-20 mm, respectively. A 10 nm laye
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