La doped lead zirconate titanate (P(L)ZT) is a ferroelectric material which has perovskite structure. The P(L)ZT film is one of the promising materials applicable to capacitors in memory devices, such as dynamic random access memory (DRAM) and ferroelectric non-volatile memory (FRAM), because of its high dielectric constant, high breakdown strength, and hysteresis properties. P(L)ZT films have been fabricated mainly by sputtering, sol-gel, and CVD method. Pt often has been selected as a bottom electrode for the ferroelectric film because of its highelectric conductivity and good stability in high temperature oxidizing ambient. Ti and Ta have been used as an adhesive layer to promote the Pt adhesion to the $SiO_2$ layer.
In this study, P(L)ZT films were deposited by DC reactive multi-target sputtering method using Pb, La, Zr, and Ti metal targets on Pt and RuO2 bottom electrodes. The compositions of P(L)ZT films can be controlled easily by using single metal targets. Growth behavior on the early stage of P(L)ZT film deposition, which can highly influence on the entire P(L)ZT film properties, has not been investigated satisfactorily, even though deposition charateristics and electrical properties of P(L)ZT fims have been extensively studied. So, basic deposition and electrical properties were firstly studied varying deposition conditions, such as oxygen flow rate, deposition temperature, and target power of La and Zr metal target. Secondly, ultra thin single oxide seed layer was introduced to ensure pure perovskite phase formation prior to P(L)ZT film deposition. The phase formation and electricalproperties of P(L)ZT films deposited on the various oxide seed layers were compared each other. And the different growth and eletrical behavior of those films was analyzed by microscopical and compositional analysis.
The other main topic focused in this study is the degradation properties, such as fatigue and imprint, of P(L)ZT films. Fatigue phenomenon means the polarization reduction from the original value by appling cyclic pulse to ferroelectric material. Imprint is caused by asymmetry of polarization, which can be generated in as-deposition state or by one-directional applied pulse polarity. The above two properties are major obstacles to development of the FRAM device. Two methods have been examined to prevent fatigue phenomenon. One is using oxide electrode and the other is adding adequate dopants to mimimize the effect of oxygen vacancy in ferroeletric material. Ru$O_2$, LSCO, Ir$O_2$ can be the major candidates of oxide electrodes. And, dopants, such as La, Nb, Zn and Sb, have been used to reduce the defect density in the P(L)ZT films.
In this study, Ru$O_2$ electrode and La dopant were used for enhancing fatigue property of P(L)ZT film. The major factor affecting fatigue property was investigated and the fatigue behaviors in bipolar and unipolar cycling pulse were analyzed. And the origin of voltage shift of hysteresis loop, which leads to imprint failure in FRAM device, was investigated.
