Characterization of Metalferroelectric-Insulator-Semiconductor Structures Based on Ferroelectric Langmuir-Blodgett Polyvinylidene Fluoride Copolymer Films for Nondestructive Random Access Memory Applications

Ferroelectric field effect transistors (FeFETs) have attracted much attention recently because of their ability to combine high speed, low power consumption, and fast nondestructive readout with the potential for high density nonvolatile memory. The polarization of the ferroelectric is used to switch the channel at the silicon surface between states of high and low conductance. Among the ferroelectric thin films used in FET devices; the ferroelectric copolymer of Polyvinylidene fluoride, PVDF (C 2 H 2 F 2), with trifluoroethylene, TrFE (C 2 HF 3), has distinct advantages, including low dielectric constant, low processing temperature, low cost and compatibility with organic semiconductors. By employing the Langmuir-Blodgett technique, films as thin as 1.8 nm can be deposited, reducing the operating voltage. An MFIS structure consisting of aluminum, 170 nm P(VDF-TrFE), 100 nm silicon oxide and n-type silicon exhibited low leakage current (~1×10-8 A/cm 2), a large memory window (4.2 V) and operated at 35 Volts. The operating voltage was lowered through use of high k insulators like cerium oxide. A sample consisting of 25 nm P(VDF-TrFE), 30 nm cerium oxide and p-type silicon exhibited a 1.9 V window with 7 Volt gate amplitude. The leakage current in this case was considerably higher (1×10-6 ii iii A/cm 2). The characterization, modeling, and fabrication of metal-ferroelectric-insulator semiconductor (MFIS) structures based on these films are discussed. iii iv TABLE OF CONTENTS I. iv v ACKNOWLEDGMENTS I would like to express my special gratitude to my advisor Professor Stephen Ducharme for granting me the opportunity to pursue a Ph. D. degree at UNL. His advice, insight and experience was invaluable and vital to the completion of this work. I am grateful to my mother, sister, friends and family for their love and support. willingness to aid me with general deposition protocols made possible the fabrication of films of excellent quality. I would like to thank Professor Ned Ianno for his expert advice in regards to semiconductor device physics and device processing in general. for being good friends and colleagues and for generously sharing laboratory equipment. A material is said to be ferroelectric when it has a spontaneous polarization and at least two stable polarization states in the absence of an external electric field and can be shifted from one to another by a sufficiently large field known as the coercive field. 1 The polarization states form a basis for Boolean code and the stability of these …