PZT/Ruthenate Electrode Heterostructures Grown by MOCVD and Their Ferroelectric Properties

• Main Authors: Wu Da-Ren, 吳達仁
• Other Authors: Tsai Dah-Shyang
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/46796151440627048066

碩士 === 國立臺灣科技大學 === 化學工程系 === 90 === This thesis reports our efforts on synthesis of calcium and strontium ruthenates, which serve as bottom electrodes for the PZT ferroelectric capacitor, and the relations between the microstructure and the ferroelectric properties of PZT/Ca, SrRuO3/Pt and PZT/Ca, SrRuO3/SiO2 heterostructures. CaRuO3 and SrRuO3 thin films are deposited on two substrates, Pt/Ti/SiO2/Si and SiO2/Si, in a hot-wall reactor, using precursors of Ca(DPM)2, Sr(DPM)2, and Ru(C5H5)2. The deposition temperature is 680°C for CaRuO3 and 700°C for SrRuO3. Further annealing is necessary to convert the unreacted oxides in both as-deposited thin films to a single phase. The annealing is 765°C 2 hours for CaRuO3 and 700°C 2 hours for SrRuO3. The higher annealing temperature of CaRuO3 is attributed to the lower diffusivity of Ca2+, compared with Sr2+. The grain sizes of CaRuO3 and SrRuO3 are generally higher on Pt/Ti/SiO2/Si than those on SiO2/Si. The surface roughness of SrRuO3 on Pt/Ti/SiO2/Si is the highest among four bottom electrodes. The sheet resistance by four-point probe measurement of SrRuO3 thin film 910 mW/cm is lower than CaRuO3 thin film 1810 mW/cm, even though the resistance of CaRuO3 single crystal in literature is lower than that of SrRuO3. Both of the PZT films grown on CaRuO3 and SrRuO3 exhibit preferred orientation in the (101) plane. The preferred orientation of PZT film on CaRuO3 seems to be more apparent. The interdiffusion between oxide electrode and PZT film is studied by SIMS. The diffusion depth of PZT into CaRuO3 is less than that of SrRuO3, in other words, CaRuO3 thin film is more effective as a diffusion barrier. The remnant polarization of PZT thin film on CaRuO3 is generally lower than that on SrRuO3, disregard the conducting oxide is on Pt/Ti/SiO2 or SiO2. The coercive field of PZT thin film on CaRuO3 is generally larger than that on SrRuO3. The less ideal hysteresis loop on CaRuO3 bottom electrode is attributed to the higher lattice mismatch between CaRuO3 and PZT, which reveals itself in the width of two overlapped X-ray diffraction peaks, (001) and (100). One plausible reason for a larger coercive field of PZT thin film on CaRuO3 is because of its higher resistance. The leakage current densities of PZT thin films on CaRuO3/SiO2/Si 2.4´10-7 A/cm2 and SrRuO3/SiO2/Si 5.0´10-7 A/cm2 (2V) are much lower than those on CaRuO3/Pt/Ti/SiO2 1.6´10-3 A/cm2 and SrRuO3/Pt/Ti/SiO2 2.0´10-6 A/cm2 (2V). It could be due to the higher roughness of CaRuO3 and SrRuO3 on Pt/Ti/SiO2. The ideal performance of PZT/oxide/Pt/Ti/SiO2 on polarization fatigue testifies that the ferroelectric capacitor with a high leakage current density will not fatigue.