Effect of PLT Buffer Layers on the PZT Thin Films for Scaling-Down Ferroelectric Materials
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Effect of PLT Buffer Layers on the PZT Thin Films for Scaling-Down Ferroelectric Materials Dong Hua Li, Eun Sun Lee, Hyun Woo Chung, Byung Du Ahn, and Sang Yeol Lee Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Korea ABSTRACT The Hysteresis characteristics of below 400 nm- thick Pb(Zr0.52Ti0.48)O3 (PZT) thin films grown on Pt (111) /Ti/SiO2/Si substrates have showed very poor with remanent polarization of 1~3 µC/cm2 in our previous research. To study the further scaling-down, we introduced the method of our previous research that the (Pb0.72La0.28)Ti0.94O3 (PLT) buffer layers play an important role in enhancing the ferroelectric properties of the PZT thin films. As a result, the remanent polarization of 300 nm-thick PZT thin films with the 10 nm-thick PLT buffer layers have showed 32 µC/cm2 at applied voltage of 8 V and 24 µC/cm2 at applied voltage of 5 V. Inserted the PLT seed layers between the PZT thin films and substrate, the hysteresis characteristics of PZT thin films were improved a lot. The dielectric and leakage current properties of PZT thin films were also investigated. INTRODUCTION In recent years, a lot of studies still have been carried out for the ferroelectric materials in the development of new materials for the FRAM (Ferroelectric Random Access Memory) technology fields. Lead zirconate titanate, the Pb(Zr0.52Ti0.48)O3 (PZT) ferroelectric thin films have been studied over the past few years as next generation materials for use in nonvolatile memories [1,2]. Because of their excellent ferroelectric properties, such as high remanent polarization [2] and low coercive filed, PZT thin films are possible to use in non-volatile memories applications. The high remanent polarization determines the data storage capacity of memories, and low coercive field can lead low operation switching voltage. In order to apply to the large-scale integrated circuit (LSI), the size of the device must become smaller and smaller as much as possible. So, the scaling-down studies are most important to attain the purpose of practical applications. However, the scaling-down studies of ferroelectric materials were difficult to carry out because of the poor remanent polarization and high leakage current. Pb(Zr0.52Ti0.48)03 (PZT) thin films with the buffer layers have the excellent characteristics of remanent polarization and leakage current. It has been reported that the (Pb0.72La0.28)Ti0.93O3 (PLT) thin films acted as the buffer layers are played an important role in the enhancement of the ferroelectric properties of PZT films as reported by E. S. Lee et al [3]. It is mainly due to the
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similarity in chemical and structural characteristics between the PLT buffer layers and the PZT thin films. These properties are helpful to form better crystallization of the PZT thin films, which can make the perovskite phase of PZT thin films strong and the ferroelectric properties enhance. In this study, we introduced 10 nm-thick PLT buffer layers on the PZT capacitors and examined
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