Papers

ICMCTF1999 Session H4-2: Ferroelectric and Piezoelectric Thin Films

Wednesday, April 14, 1999 1:30 PM in Sunrise Room

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		H4-2-1 Pulsed Laser Deposition of (Ba,Sr)TiO₃ Thin Films for Tunable Microwave Applications J. Horwitz, W. Chang, W. Kim, J.M. Pond, S.W. Kirchoefer, D.B. Chrisey (US Naval Research Laboratory) Ba_{x√sub 1-x}TiO₃ (BST) thin films (~0.5 µm thick) are currently being used to develop a new class of tunable microwave circuits by taking advantage of the large DC electric field dependence of the dielectric constant. BST films have been deposited onto (100) MgO and LaAlO₃ single crystal substrates using pulsed laser deposition (PLD). The dielectric constant and loss tangent of the ferroelectric film were determined by using silver interdigitated capacitors patterned on top of the ferroelectric films. A direct relationship is observed between film structure and dielectric properties at microwave frequencies (≤20 GHz). As-deposited films are single phase and (100) oriented as determined from x-ray diffraction. While films deposited on MgO and LaAlO₃ substrates are microstructurally very similar, their dielectric properties (? (O), ? (V) and tanδ) are quite different. These differences originate from variations in film stress caused by several factors which include the film substrate lattice mismatch, differences in the thermal expansion coefficient between the film and the substrate, and oxygen and cation vacancies. The net stress field limits the extent of ionic polarization in the BST film which in turn, determines how strongly the dielectric interacts with both the DC and AC electric fields. Improvements in BST film properties at microwave frequencies (increased response to DC electric filed and reduced loss tangent) can be achieved by reducing overall film stress with a thin (~100 Å) polycrystalline BST buffer layer.
2:10 PM		H4-2-3 Ferroelectric BST Thin Films for DRAM's Applications G.A. Hirata, D. Madrigal, J.M. Olivares (CECIMAC-UNAM); J. McKittrick (AMES-UCSD) The microstructural and ferroelectric properties of bulk Ba_{1-x√sub x}TiO₃ and thin-films prepared by excimer laser deposition on SiO₂/c-Si an Pt/Ti/SiO₂/c-Si are reported in this work. The films were amorphous in the as-deposited condition and crystallized randomly after annealing at 550°C. The x-ray diffraction patterns of the films and the ablation target match exactly indicating that excellent stoichiometry preservation is attained by pulsed laser deposition. Smooth and uniform films showing few cracked areas were obtained on SiO₂/c-Si substrates, while films deposited on Pt/Ti/SiO₂/c-Si substrates presented wider cracks that were promoted during the annealing process due to the thermal expansion mismatch between the films and the Pt coated substrates. The Curie temperature of the films was around -31°C with a maximum dielectric constant of 180. Experimental conditions of BST films deposited on ruthenium oxide electrodes will be also presented
2:30 PM		H4-2-4 The Influence of Excess Pb and O on the Ferroelectric Properties of Pb(Zr_0.52 Ti_0.48 )O₃ Thin Films H.H. Park, S.M. Ha (Yonsei University, KOREA); T.S. Kim (KIST, KOREA) In the fabrication of PZT thin films for the application to FRAM, there have been a lot of works to improve the electrical properties of PZT, especially fatigue property by preparing PZT film with excess contents of Pb and O. Besides the prevention from the creating of defect by volatilization, excess Pb and O seems to contribute to improved crystallinity and electric properties of PZT films. But there is no detail study about the exact role of excess Pb and O on the improved properties. In this work, we performed the study on the effect of excess Pb and O contents on the ferroelectric properties of Pb(Zr_0.52Ti_0.48)O₃/Pt system. PZT films were sputter-deposited from a target containing 50%, 75% and 100% excess Pb and O with varying substrate annealing temperature from 20°C to 520°C. Successive post-anneal treatments were done at 600°C or 700°C to improve the ferroelectric properties of thin films. The compositional and structural evolutions according to the anneal were investigated. Excess Pb and O was observed to form a-PbO₂phase at low temperature-deposition and it decomposed at elevated temperature. The electrical properties of PZT thin films were characterized through P-E hysteresis curves, dielectric constant and loss, and fatigue measurements. Through the above analyses, the effect of excess Pb contents on the microstructure and electrical properties of PZT film could be explained.