Resistive Switching Based On P（VDF-TrFE） And TiO₂ Thin Films

Recently, advances in integrated circuits technology have been continuously pushing forward the development of information technology. At the same time, because portable devices become more and more popular, enhanced performance of nonvolatile memories, such as high speed, long-time reliability, low power consumption, high storage density, low cost and so on, are urgently required. According to the Moore’s law, the size of a single semiconductor device in the integrated circuits is reduced and the density doubles every 18-24 months. With the continuous miniaturization, the size of conventional semiconductor memory node is approaching its physical limit. Currently, resistive random access memory, based on the change of resistance between a high and a low state, is considered one of the best choice for the next generation memory because of its high storage density, high read and write speeds, low power consumption, good fatigue characteristics, simple device fabrication, and its compatibility with conventional CMOS technology. However, memory material selection, device fabrication, and mechanism of the resistive switching remain to be clarified. This paper focuses on two aspects:(1) spin-coated FePt:P(VDF-TrFE) thin film and its resistive switching properties; (2) Pulsed Laser Deposition (PLD)-deposited TiOx/PZT heterostructures and the relation between the TiOx deposition parameters and the resistive switching in Pt/TiOx/Pb(Zr0.52Ti0.48)O3/ (La0.7Sr0.3)Mn03 devices. Major conclusions include:1. Research on the effect of annealing temperature on the surface morphology of spin-coated P(VDF-TrFE) thin film suggests that high annealing temperature favors the full extension of the P(VDF-TrFE) polymer chain. By mixing chemical-solution-method-prepared FePt nanocrystals solution with P(VDF-TrFE) solution, FePt:P(VDF-TrFE) composite thin film is spin-coated on Si substrates. Electrical measurements reveal that in Pt/FePt:P(VDF-TrFE)/Pt devices, the FePt nanoparticles act as passing channels for electrons, and the device exhibit unipolar resistive switching. One obstacle to be ovecom in the processing is the conglomeration of nanoparticles that greatly lowers the storage density.2, TiOx/PZT/LSMO heterostructures are deposited by PLD on (001) SrTiO3 substrates. LSMO acts as bottom electrodes and the TiOx layer are deposited in different atmosphere. The evolution of resistive switching characteristics of TiOx/PZT bilayers are studied as functions of TiOx deposition temperature and oxygen chamber pressure. Bipolar resistive switching characteristics of Pt/TiOx/PZT/LSMO heterostructures are observed to vary with TiOx deposition parameters, from an interface-controlled ferroelectric diode behavior to a bulk-controlled conductive filament behavior when the TiOx deposition temperature increases or the oxygen chamber pressure decreases. The observations are discussed in terms of the concentration and migration of oxygen vacancies in the TiOx layer.