Investigation of Ferroelectric Nanodots for Memory Applications

1. Investigation of Ferroelectric Nanodots for Memory Applications Timothy A. Morgan, ZhaoquanZeng, Greg Salamo Motivation & Approach Substrate Selection & Preparation Characterization & Results Examining commercially available substrates for appropriate mismatch is necessary. Understanding every substrate’s crystal structure and symmetry is essential in undrestanding what plane is required to grow on. The goal is finding a cubic or tetragonal unit cell with a lattice parameter having a ~5-7% mismatch. Beyond finding the appropriate plane, examining the substrate surface for growth ensued. Ferroelectric nanodots are an exciting material to investigate for memory applications. FeRAM (Ferrolecetric random access memory) has been shown to have advantages over traditional DRAM (dynamic random access memory) through data retention, power reduction and quicker access times. Improving properties such as fatigue and density are goals for FeRAM to improve. Experimentally, investigating ferroelectric nanodots to realize the vortex phase and determining the switching characteristics is the goal of this research. • Initial growths show dots on MgO, YAlO3 (YAO) and LaAlO3 (LAO) • MgO substrate surface roughness is minimized at annealing temperature of 850 C for 12 hours with oxygen flow • Growths on smoother MgO surface have yet to show dots • Dots have formed on unprepared MgO • XPS results of dot sample confirm BTO formed YAlO3 (220) LaAlO3 (110) BTO on YAlO3 BaTiO3 Oxide Substrate Tensile • Future • Investigate MgO surface characteristics that are optimal for BTO dot formation • Investigate LAO substrates for dot growth • Optimize growth conditions for consistent dot formation • Investigate composition of individual nanodots Compressive Tensile The Stranski-Krastanov growth mode forms self-assembled nanodots due to strain built up from lattice mismatch to the substrate. Barium titanate (BTO) is deposited onto an oxide substrate utilizing the molecular beam epitaxy (MBE) technique. Dots can form from both compressive (negative mismatch) and tensile (positive mismatch) strain applied from an appropriate substrate. MgO @ 700° C 12 hrs BTO on MgO MgO @ 850° C 12 hrs Obtainining an atomically flat surface on our substrate is our goal. We have worked on preparing MgO through annealing with oxygen flow. • Shuttered RHEED Technique • Perovskite structure (ABO3) • Alternating layers of AO & BO2 • Acknowledgements • Rob Sleezer • David Monk • Morgan Ware • BTO on MgO Composition analyisis • Ba, Ti & O peaks found on surface • No substrate impurities found MgO @ 1100° C 12 hrs STO (100) substrate BaO layer on STO (100) TiO2 layer on STO (100)