Growth And Properties Of La_0.5Sr_0.5CoO₃/Pb(Zr_0.52Ti0.48 O₃/La_0.5Sr_0.5CoO₃ Integreted Ferroelectric Thin Films

Compared with the traditional E2PROM, FLASH and any other non-volatile memories, the new kinds of non-volatile ferroelectric memories (FRAM), which are very suitable for the requirements of embedded applications, have many more better advantages, such as lower operating voltage, faster read-write operation, lower power consumption, more long time retention and so on. As the core of integrated ferroelectric device, ferroelectric thin film is the key to fulfill the FRAM. Therefore, in order to improve the fatigue properties of the PZT ferroelectric thin films used currently in the ferroelectric memories, on the one hand, this paper mainly focused on the preparation of the LSCO targets, which were used to prepare the LSCO thin film layer for the LSCO/PZT/LSCO sandwiched ferroelectric thin films by the RF-magnetron sputtering technology. On the other hand, two main parameters during in the sputtering technology had been optimized by the experimental analysis and research, substrate temperature and sputtering power, respectively. Thirdly, spontaneous nucleation process during the film growth stage had also been researched according to the thermodynamics theory.By analyzing the impact on the critical core size r *and the free-energy changeΔG *, which was coming from the substrate temperature T and the sputter deposition rate U, we explored the relationship between the T, U and the nucleation process during the growth of films. As a result, with the increase of substrate temperature T, the critical core size r * of new phase and the free-energy changeΔG * barrier will all be larger. Massive island structure will form firstly during in the high-temperature sputtering deposition process of thin film. To raise the sputtering deposition rate U will effectively reduce the r * andΔG *, so that the grain of thin films will be refined.The best threshold values to prepare La_0.5Sr_0.5CoO₃ targets by the method of sol-gel self-combustion for RF-magnetron sputtering LSCO buffer layer of the ferroelectric thin film LSCO/PZT/LSCO have been got, sintering temperature of 1200℃and La excess coefficientλ= 0.03, respectively. The targets on this optimum technology could own more pure phase, better uniformity of grain, and to be compact with fewer voids. Even more, the minimum resistivity of the LSCO targets could be achieved to 0.145 m? ? cm.The substrate temperature and sputtering power were appropriately changed during the RF-magnetron sputtering technology for LSCO thin film buffer layer. Through the comparison and analysis about the phase structure, micro-structure properties, ferroelectric and fatigue characteristics of the LSCO/PZT/LSCO sandwiched ferroelectric films prepared by RF-magnetron sputtering, the optimum substrate temperature and sputtering power during in the sputtering process all have been summarized, 600℃and 100 W, respectively. In this condition, the thin films along to the (110) preferred orientation could be of more pure phase. Furthermore, PZT ferroelectric layer could be well crystallized, and the grains of PZT could own better uniformity, clearer boundary and so on. At the same time, the grains could also be compact with fewer voids. In terms of electrical properties, the remnant polarization and coercive voltage of the ferroelectric LSCO/PZT/LSCO (600℃, 100 W) films could reach up to 80μC/cm2 and 4.3 V, respectively. For another hand, after 1010 polarization reversal, the residual polarization could still maintain 96% to the original polarization.