Dual-gate thin-film transistors for logic and sensors

PhD ceremony: Mr. M.-J. Spijkman, 16.15 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Dual-gate thin-film transistors for logic and sensors

Promotor(s): prof. D. de Leeuw, prof. P. Blom

Faculty: Mathematics and Natural Sciences

Thin-film transistors (TFT) are currently mainly used as pixel drivers in flat panel displays used in televisions, monitors and mobile phones. TFT technology is used to manufacture large area electronics on cheap substrates. Currently, amorphous silicon is used as the semiconductor, but research is aimed at metal oxides and organic polymers as possible replacements.

Organic polymers are attractive materials because of their ease of processing and mechanical flexibility. The polymers can be printed on a roll-to-roll process, potentially allowing extremely cheap electronics. Applications are foreseen in displays, contactless RFID tags and as sensors.

For any application, control of the threshold voltage, where the transistor switches from the on to the off state, is crucial. Here, an additional, second gate was used to influence the charge transport and externally set the threshold voltage. The resulting dual-gate transistors were used in both logic and sensing applications.

In organic integrated circuits, the limiting factor is the large spread in transistor parameters, such as the threshold voltage, resulting in a low noise margin. The low noise margin limits the maximum circuit size, reducing the functionality. With dual-gate transistors, the threshold voltage could be set, which increased the noise margin by almost an order of magnitude.

As sensors, dual-gate transistors were demonstrated as pH sensors. The capacitive coupling between the gate dielectrics was advantageously used to amplify the response of existing ion-sensitive field-effect transistors (ISFETs). The main obstacle to use of ISFETs as label-free biosensors, their low sensitivity, has now been negated.