Detection principles of biological and chemical FET sensors.

Charge carrier control is a key issue in the development of electronic functions of semiconductive materials. Beyond the simple enhancement of conductivity, high charge carrier accumulation can realize various phenomena, such as chemical reaction, phase transition, magnetic ordering, and superconductivity. Electric double layers (EDLs), formed at solid-electrolyte interfaces, induce extremely large electric fields. This results in a high charge carrier accumulation in the solid, much more effectively than solid dielectric materials. In the present review, we describe recent developments in the field-effect transistors (FETs) with gate dielectrics of ionic liquids, which have attracted much attention due to their wide electrochemical windows, low vapor pressures, and high chemical and physical stability. We explain the capacitance effects of ionic liquids, and describe the various combinations of ionic liquids and organic and inorganic semiconductors that are used to achieve such effects as high transistor performance, insulator-metal transitions, superconductivity, and ferromagnetism, in addition to the applications of the ionic-liquid EDL-FETs in logic devices. We discuss the factors controlling the mobility and threshold voltage in these types of FETs, and show the ionic liquid dependence of the transistor performance.

Electric-double-layer field-effect transistors with ionic liquids.

Buried electrodes and protection of the semiconductor with a thin passivation layer are used to yield dual-gate organic transducers. The process technology is scaled up to 150-mm wafers. The transducers are potentiometric sensors where the detection relies on measuring a shift in the threshold voltage caused by changes in the electrochemical potential at the second gate dielectric. Analytes can only be detected within the Debye screening length. The mechanism is assessed by pHmeasurements. The threshold voltage shift depends on pH as DVth¼(Ctop/Cbottom)T58mV per pH unit, indicating that the sensitivity can be enhanced with respect to conventional ion-sensitive field-effect transistors (ISFETs) by adjusting the ratio of the top and bottom gate capacitances. Remaining challenges and opportunities are discussed.

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Dual-Gate Organic Field-Effect Transistors as Potentiometric Sensors in Aqueous Solution

The first dual-gate thin-film transistor (DGTFT) was reported in 1981 with CdSe as the semiconductor. Other TFT technologies such as a-Si:H and organic semiconductors have led to additional ways of making DGTFTs. DGTFTs contain a second gate dielectric with a second gate positioned opposite of the first gate. The main advantage is that the threshold voltage can be set as a function of the applied second gate bias. The shift depends on the ratio of the capacitances of the two gate dielectrics. Here we review the fast growing field of DGTFTs. We summarize the reported operational mechanisms, and the application in logic gates and integrated circuits. The second emerging application of DGTFTs is sensitivity enhancement of existing ion-sensitive field-effect transistors (ISFET). The reported sensing mechanism is discussed and an outlook is presented. Dual-gate thin-film transistors (DGTFTs) have gained popularity in recent years. The additional second gate allows controlled shifting of the threshold voltage. The shift depends on the ratio of the capacitances of the two gate dielectrics. We summarize the reported operation mechanism and review the application of DGTFTs in both integrated circuits and sensors. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Dual‐Gate Thin‐Film Transistors, Integrated Circuits and Sensors

This paper reviews recent advancements in the field of organic electronics. Performance of p- and n-type conducting polymers and small molecule organic semiconductors is presented primarily in terms of mobility and current on/off ratio. Moreover, it presents a deep insight into different organic/inorganic materials used for the dielectric layer, electrodes and substrate for thin film transistors (TFTs). The electrical characteristics and performance parameters of single and dual gate structures are compared. In addition, performance dependence of organic TFT (OTFT) is discussed on the basis of contact resistance, channel length and thickness of the active layer. The paper thoroughly discusses several important applications of OTFTs including inverter, organic static random access memory, radio frequency identification tag and DNA sensors. It also includes several limitations and future prospects of organic electronics technology.

P. Fonteijn

Papers

Device characteristics of polymer dual-gate field-effect transistors