Fabrication And Characterization Of Ferrelectric Tunneling Junction Based On PZT Films

With the improvement of memory device performance requirements, Flash memory technology is increa singly unable to meet people’s needs. Since the ferroelectric memories with higher storage density, lower power consumption, faster read and write rates attract widespread attentions. The commercial ferroelectric memories achieve to write and read data through the ferroelectric polarization reversal to change the film capacitance. However, destructive data readout limite the development of this type ferroelectric memories. Ferroelectric tunneling junctions(FTJs) as a branch of the ferroelectric memories can achieve non-destructive data readout and when the polarization performance of the ferroelectric barrier is weak, FTJs can still work. It is greatly increasing the life of the devices. A new round of research boom is starting. In this paper, the perovskite-type PZT films as a ferroelectric barrier were farbricated by pulsed laser deposition(PLD) on(001)Sr TiO3(STO) substrate and the(001) Nb:Sr TiO3(NSTO) substrate respectively, to explore how the parameters and the electrode materials to impact the structure and electrical properties of ferroelectric tunneling junctions.1. Firstly, STO substrate surface was formed step- flow morphology, then SrRuO3(SRO) and Pb(Ti52Zr48)O3(PZT) films were fabricated on STO substrate. The results showed that the substrate temperature and oxygen partial pressure significantly affected oriented crystallization, ferroelectricity and surface morphology during the films deposited. The Optimum parameters of SRO and PZT films were 700 ℃, 20 Pa and 600 ℃, 20 Pa,respectively.2. With optimum parameters of PZT films,the different thickness(~134.5 nm,86.5 nm, 41 nm å'Œ 8 nm) of PZT films were fabricated. The results show that: the remanent polarization of PZT films decreases when films thickness decreases. Au/Ti/(8 nm) PZT/SRO/STO tunneling junction have a maximum value of about 126 tunneling resistance(TER) value after ±6 V poling. The pole voltage affect the ferroelectricity of the barrier layer, and then affect the TER, excessive pole voltage will destroy the ferroelectricity of the barrier layer, then the vale of TER decreases.3. With optimum parameters of PZT films in the third chapter,8 nm PZT films were farbricated on NSTO substrate. Au/Al as NSTO substrate ohmic contact electrode and SRO and Au/Ti as top electrode were fabricated two ferroelectric tunneling junctions, combined with Au/Ti/PZT/SRO/STO tunneling junction to explore the effects of electrode materials on TER, the reasons of the current changes and research electron transport mechanism. The results showed that: Au/Ti/PZT/NSTO tunneling junction has a maximum TER of about 1120,SRO/PZT/NSTO tunneling junction has a maximum TER of about 150. The reason of current change is mainly due to different shield length of the top and bottom electrodes. They can cause the change of the ferroelectric barrier layer barrier height. Due to the emergence of semiconductor electronic depletion region, the semiconductor substrate can increase TER. It can increase the width of the barrier. Electron transport mechanism of Au/Ti/PZT/SRO/STO and Au/Ti/PZT/NSTO are Schottky emission.