Low Voltage Organic Field Effect Transistors for Digital Logic Operations and Sensors

Abstract

This thesis investigates the practical applications of low-voltage organic field-effect transistors (OFETs) in logic circuits and as sensors for early pathogenic infection detection in crops. Moreover, an in situ probing technique has been established to gain a deeper understanding of the complex interface at the boundary of the electrolytes and organic semiconductors. A 10-fold enhancement in the field-effect mobility of poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) OFETs from 0.01 cm2 Vand#8722;1 sand#8722;1 to 0.1 cm2 Vand#8722;1 sand#8722;1 by surface treatment of the SiO2 gate dielectric has been attributed to a reduction in trap-DOS and contact resistance through quantitative analytical methods. Despite this improvement, the operating voltage remains high (~15 V). To address this, we introduce a low-temperature solution-processed ZrO2 gate dielectric, enabling operation at lt1 V with an impressive mobility of up to 0.17 cm2 Vand#8722;1 sand#8722;1. Alternatively, imidazolium ionic liquids (IL) as gate dielectric yield OFETs with high hole mobility (~20.2 cm2 Vand#8722;1 sand#8722;1), low threshold voltage (~0.6 V), and high transconductance (gt1 mS). The effective gate bias voltage in the IL-gated OFETs was measured in situ to gain an insight into the formation of the electric double layer at the IL/semiconductor interface. Moreover, the trap-DOS at the IL/semiconductor interface has been calculated and correlated with the performance of the IL-gated OFETs. The high transconductance of IL-gated OFETs has been exploited for the fabrication of IL-gated logic inverters, which exhibit high gain (~10 V/V), near-ideal switching voltage (0.5 V - 0.7 V), and an excellent noise margin (gt55%). Concurrently, ZrO2-gated PBTTT-C14 OFETs serve as a low-power sensing platform for detecting volatile organic compounds during host-pathogen interactions in infected rice plants. this thesis advances the understanding of low-voltage OFET operating mechanisms and charts new avenues for the widespread adoption of organic semiconductor-based devices.