Investigation of Ferroelectric Nanodots for Memory Applications

1. Investigation of Ferroelectric Nanodots for Memory Applications Timothy A. Morgan, ZhaoquanZeng, Greg Salamo Motivation Ferroelectric nanodots are an exciting material to investigate for memory applications. FeRAM has been shown to have advantages over traditional DRAM through data retention, power reduction and quicker access times. Improving properties such as fatigue and density are goals for FeRAM to improve. Theoretical work by Bellaiche et al have shown the possibility of increasing FeRAM density to 60 Tb/in2 through a vortex phase in Pb(Zr,Ti)O3nanodots that have bistable states switchable through static inhomogeneous electric fields or time varying magnetic fields1,2. Experimentally, investigating ferroelectric nanodots to realize the vortex phase and determining the switching characteristics is the goal of this research. Dot Formation Technique Substrate Selection Utilizing SK growth mode requires specific substrates. However, not all crystals have a simple cubic structure like strontium titanate (STO) at room temperature. Determining which crystal lattices had a square of atoms to grow was necessary. In addition, finding the appropriate mismatch with BTO. Compressive Tensile YAlO3 (220) LaAlO3 (110) The Stranski-Krastanov growth mode will be used to form self-assembled ferroelectric nanodots. MBE will be utilized to control the deposition of barium titanate (BTO) on different oxide substrates. The key will be choosing substrates with lattice mismatch ~5-7% and preparing the substrate surface for dot growth. 1. Naumov, I. I., Bellaiche, L., and Fu, H., Nature432 (7018), 737 (2004) 2. Naumov, I., Bellaiche, L., Prosandeev, S., Ponomareva, I., Kornev, I., United States of America Patent No. US 2008/0130346 A1 (2008). • Summary • Preliminary growths indicate BTO dot formation is possible • Optimize substrate surfaces for BTO dot growth • Optimizie growth conditions for BTO dots • Examine ferroelectric properties Substrate Preparation With several choices of substrates, preparing the substrates for growth is essential. We have worked on preparing MgO and analyzing the surface for roughness and composition. MBE Growth of Ferroelectrics Riber 32 MBE System Shuttered RHEED Technique • Addon RF Oxygen Plasma Soure • In-situ Omicron STM/AFM • kSA 400 RHEED • kSABandiT Temperature Monitor • SRS RGA • Crystal Eyes 7.0 Software • Inficon QCM (future) • SVTA Ozone Delivery System MgO @ 700° C 12 hrs Growing a monolayer at a time is important for perovskite structures. MgO @ 850° C 12 hrs Shuttered RHEED Technique Growing a monolayer at a time is important for perovskite structures. • Acknowledgements • Rob Sleezer • David Monk • Morgan Ware MgO @ 1100° C 12 hrs STO (100) substrate BaO layer on STO (100) TiO2 layer on STO (100)