Tomas G. Bäcklund

Operating principle of polymer insulator organic thin-film transistors exposed to moisture

The operating principle of a hygroscopic insulator field-effect transistor has been investigated. The semiconductor poly(3-hexylthiophene) shows an increased conductivity after applying the poly(vinylphenol) (PVP) insulator, which is attributed to an interfacial dipole layer caused by the permanent dipole moment in PVP. The effects of solvents on the transistor device indicate that low molecular weight protic solvents such as water, methanol, and ethanol affect the I-V characteristics significantly, in contrast to 1-propanol and aprotic solvents such as acetonitrile. The presence of a protic solvent inside the device insulator gives rise to an ion-assisted modulation of the transistor source-drain current.

Current modulation of a hygroscopic insulator organic field-effect transistor

We have fabricated solution processable polymer transistors with high conductivity, requiring only a few volts for obtaining good current modulation. The devices can be fabricated and operated in air and the operation is greatly enhanced in humid atmosphere. Devices reach an On∕Off ratio of about 600 and a subthreshold swing of 500mV per decade operating on voltages less than 2V. In this letter the mechanism behind the current modulation is investigated, and we show that the current is modulated through ion-assisted oxidation and reduction of the semiconductor by ions moving vertically in the insulator material to the transistor channel.