Aplicação de novos materiais em transistores de efeito de campo ferroelétricos

Abstract

In this work, we investigated the electrical properties of the polyelectrolyte PSS in its sodium form (PSS-Na, Polystyrene sulfonic in the sodium form) and acid form (PSS-H, polystyrene sulfonic in the acid form) and also doped with Fe3+ for application in Ferroelectric Field Effect Transistors (Fe-FET). The PSS-Na was acquired from Aldrich® and PSS-H was obtained through an ion exchange using the PSS-Na. The Fe(PSS)3 was obtained by adding Fe(OH)3 in solution of PSS-H. The films were deposited on FTO (tin oxide doped with fluorine) with a JFET layout-type on substrate of glass. The deposition technique used was the casting. Samples were also processed in the form of FTO/polyelectrolyte/FTO for the study of capacitance. The characterization was performed by cyclic voltammetry in solution, laser interferometry, current versus time, current density versus function of electric field applying a gate voltage, transfer curve (ID x VG) with fixed drain voltage (VD). Electrical characterizations show that the sample PSS-Na showed capacitance values of ~ 1000 times smaller than the other samples, which gives a smaller charge storage capacity compared with PSS-H and Fe(PSS)3. The Fe(PSS)3 showed higher value of dielectric permittivity. Only PSSH and Fe(PSS)3 showed ferroelectric behavior, exhibiting the former in a more characteristic curve. The PSS-Na did not show polarization dipoles, while PSS-H and Fe(PSS)3 showed peak polarization dipoles and NDR areas (Negative Differential Resistance). The application of negative gate voltage (VG) causes a significant increase in the drain current (ID), while a positive voltage causes a narrowing of the conductor channel, reducing the ID. PSS-Na did not show on state (highest conductivity) and off state (lower conductivity) due the absence of permanent polarization properties. However, PSS-H and Fe(PSS)3 showed distinction between the two states. Only the Fe(PSS)3 showed the property of retention of data. The on and off states of PSS-H e Fe(PSS)3 are not defined for positive gate voltage due the fact that the device behaves as a Bipolar Junction Transistor. This fact lead us to believe that the devices function as memory only for negative gate voltages. The samples showed low values of mobility, giving them a low speed of response with application of external electric field. Finally, the layout worked showed propitious for study of electrical properties of materials and the Fe(PSS)3 samples showed the best parameters for applications in devices like Fe-FET.