Long-term electrical characteristics of a poly-3-hexylthiophene water-gated thin-film transistor

TL;DR

This study investigates the long-term electrical stability of poly-3-hexylthiophene water-gated thin-film transistors over two months, revealing how device parameters evolve with measurement cycles and environmental factors.

Contribution

It provides detailed analysis of the stability and degradation mechanisms of P3HT WG-TFTs during extended operation, highlighting the effects of electrical stress and water immersion.

Findings

Threshold voltage shifts linearly with measurement cycles.

Mobility decreases linearly with measurement cycles.

Trap density increases gradually and partially recovers after rest.

Abstract

Organic water-gated thin-film transistors (WG-TFTs) are of great interest in developing low-cost and high-performance biosensors. The device's sensitivity to changes in measurement conditions can impair long-term operation, and care must be taken to ensure that the WG-TFT sensor response is due to an actual biorecognition event occurring on the sensing electrode. This work aims to clarify the long-term stability of a poly-3-hexylthiophene (P3HT) WG-TFT operated intermittently over two months during 5750 measurement cycles. We have evaluated the device figures of merit (FOM), such as threshold voltage, mobility, and trap density, during the whole measurement period. Short-term changes in the FOM are mainly attributed to work function changes on the gate electrode, whereas long-term changes are consistent with an increase in the semiconductor trap density. The shift in threshold voltage and decrease in mobility are found to be linear as a function of measurement cycles and caused by electrical stress, with time immersed in water having a negligible effect on the device. The trap density-of-states estimated using the subthreshold slope is similar to earlier reported values for P3HT OFETs and exhibits a gradual increase during device use and a partial recovery after rest, indicating the formation of shorter- and longer-lived traps.