Control of field-effect transistor threshold voltages by insertion of self-assembled monolayers

We report the control of the threshold voltage of field-effect-transistors (FET) by inserting a self-assembled monolayer (SAM) between the insulator and the gate electrode. The surface potentials of the SAMs, measured by Kelvin force microscopy, depended on the dipole moments of their monomer units. The SAMs were formed by chemical vapor deposition at low temperatures from various monomer units with different dipole moments. The dipole moments were determined by ab initio calculations. The FET properties, such as the threshold voltage, could be controlled by SAMs inserted between the insulator and the gate electrode. The threshold voltage shift was linearly correlated with the surface potential of the SAM. The transconductance also depended on the dipole moment of the SAM monomer unit. Therefore, altering the transconductance could also increase the range of the threshold voltage. The use of SAMs provides a simple method for controlling the properties of transistors, and can be used in thin film transistors, such as organic and oxide devices.