Organic Materials for Multifunctional Transistor-Based Devices
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ORGANIC DEVICES.
MATERIALS
FOR
MULTIFUNCTIONAL
TRANSISTOR-BASED
H.E. Katz, T. Someya, B. Crone, X.M. Hong, M. Mushrush, A. Gelperin, A.J. Lovinger, Z. Bao, A. Dodabalapur, L. Torsi, Bell Laboratories-Lucent Technologies, Murray Hill, NJ 07974 Introduction Organic field-effect transistors (OFETs) are “soft material” versions of accumulationmode silicon-based FETs, where a gate field across a dielectric induces a conductive charge channel at the interface of the dielectric with a semiconductor, between source and drain electrodes. Charge carrier mobilities >0.01 and on/off ratios >10,000 are routinely obtained, adequate for a few specialized applications such as electrophoretic pixel switches but well below standards established for silicon microprocessor technology. Still, progress that has been made in solution-phase semiconductor deposition and the printing of contacts and dielectrics1 stimulates the development of OFET circuits for situations where extreme low cost, large area, and mechanical flexibility are important. Circuits with hundreds of OFETs have been demonstrated2,3, and a prototype OFETcontrolled black-on-white “electronic ink” sign has been fabricated.4 This presentation focuses on two applications where the OFET has a transducing activity that goes beyond the typical switching function. The first is a memory element where charge stored in the gate dielectric shifts the effective gate voltage relative to the nominal applied gate voltage, producing a nonvolatile transistor effect. The second is a chemical sensor in which species adsorbed onto the semiconductor alter the drain current output of an OFET. In both cases, the organic or plastic materials used in the devices can support, or even enhance, the desired device responses. Nonvolatile OFETs The floating gate (or nonvolatile) transistor is a known device in silicon electronics.5,6 It is used as a memory element, and is based on the principle of charge storage or polarization between the gate contact and the semiconductor channel imposing a voltage in series with the gate and channel, and altering the channel voltage relative to the voltage applied at the gate contact (the “gate voltage”, Vg). The charge may be stored and/or polarized in domains within the bulk of the dielectric, or at interfaces between the gate contact and channel. There are several reasons why it might be desirable to modify an organic-based transistor so that the voltage applied to its channel is shifted relative to Vg. Besides the creation of additional device states, which can be read as stored information, floating or altered gate devices can function more effectively in certain circuits. The effective threshold voltage Vt can be brought very close to zero for applications where the available gate voltage is limited. The apparent mobility of the semiconductor can be increased, since the apparent Vg necessary to reach higher mobility states of the semiconductor can be reduced.7 P6.7.1 Downloaded from https://www.cambridge.org/core. University of Texas Libraries, on 13 Sep
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