Preparation of a New SrBi 2 Ta 2 O 9 (SBT) Chemical Solution Using Crown Ether and its Thin Film Deposition
- PDF / 1,829,012 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 18 Downloads / 114 Views
Yo-Sep Mina), June Key Lee and In-Sook Lee Microelectronics Lab, Samsung Advanced Institute of Technology, P.O. Box 11, Suwon 440-600, Korea
ABSTRACT
A new chemical solution for the deposition of SrBi 2Ta 2O9 (SBT) thin films using crown ether is proposed. Crown ether enhances the solubility of bismuth acetate in acetic acid, which makes a solvent solution possible. A metal acetate-based SBT precursor solution was prepared in acetic acid using 18-crown-6, strontium acetate, bismuth acetate and tantalum ethoxide. (115)-preferentially oriented ferroelectric SBT thin films were formed on Pt/TiO 2/SiO,/Si substrates by spin-coating with the new solution. After postannealing at 8001C, a hysteresis loop obtained from a 2000A thick SBT film with Pt electrodes showed a remanent polarization of -3ptC/cm 2 and a coercive voltage of -50kV/cm. It was shown from SIMS depth profiles that excess bismuth atoms in the SBT thin film diffused towards the Pt electrodes during post-annealing. INTRODUCTION Ferroelectric thin films have been studied for possible applications in non-volatile memory devices, especially PZT (Lead zirconium titanate) has been used as a capacitor material in ferroelectric random access memory (FRAM) fabrication. PZT thin films have
good material properties such as a high dielectric constant, large remanent polarization and low process temperature. However, severe polarization fatigue with metal contacts and retention problems remain as ongoing material issues for PZT thin films.' Recently, the bismuth layer-structured ferroelectric material SrBi 2TaO 9 (SBT) has attracted attention as a prime candidate for replacing PZT in FRAM technology ""`owing to its excellent fatigue endurance and low coercive voltage. However, shortcomings of SBT thin films such as a relatively high formation temperature (-800 °C), low remanent polarization (Pr), high porosity and surface roughness still exist. SBT thin films can be deposited by sputtering6 , Pulsed Laser Deposition (PLD)a, MOCVD7 9, and Chemical Solution Deposition (CSD).00 1 11.2. 3 Among them, CSD is the most reproducible and simplest process developed so far for obtaining high quality ferroelectric thin films. The chemical solution for SBT thin film preparation generally consists of three metal precursors and solvents to dissolve the metal precursors in a solution. In the well-known a)
Author to whom correspondence should be addressed. e-mail : [email protected]
179 Mat. Res. Soc. Symp. Proc. Vol. 596 ©2000 Materials Research Society
IBi(OAc)3 18-C-6/AcOH
Reflux at
100
°Cfor 30 min
AO
v 1 B,
IiOcsad1--
Stirring at 6 5 °C for 10min Ta(OEt)s Stirring for 10 min & filtering with 0.1 Pm filter SSBT CSD Solution7
Fig. 1. Schematic diagram of preparing SBT precursor solution
chemical solution preparation process for SBT films of Symetrix Corp., a metal 2ethylhexanoate/xylene system was utilized with a composition of 20-30% excess bismuth precursor and 20-30% deficient strontium precursor solution. The films were annealed at high temperatures of - g0
Data Loading...
