Electrical characterization of a carbon nanotube network based ferroelectric field effect transistor at different gate voltage scan rates

A ferroelectric field effect transistor (FE-FET) was fabricated using single walled carbon nanotube networks as the active semiconducting layer, and the copolymer poly (vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) as the ferroelectric gate insulator. The device was electrically characterized at different gate voltage (V_G) scan rates in the range 4mV/s < dV_G/dt  < 1V/s. Gate voltage scan rates play an important role in device operation since it controls the polarization of the gate material. This in turn affects the device on/off ratio, charge mobility, memory window width and other important device parameters. During device operation V_G was scanned as follows: -30V → +30V → -30V and resulted in the copolymer dipole switching its orientation between two polarized states (­↑↓). The resulting device transconductance curves showed p-type behavior and exhibited a hysteresis due to the FE properties of the gate insulator. At high dV_G/dt the hysteresis effect was weak due to the inability of the dipoles to switch orientation, leading to linear operation. As dV_G/dt  was lowered, the device on/off ratio and charge mobility increased, while the memory window width and sub-threshold swing decreased. Our results show that the volatile and non-volatile modes of operation can be accessed by this device  by controlling the gate voltage scan rate.