Investigation of Ferroelectric Nanodots for Memory Applications

1. Investigation of Ferroelectric Nanodots for Memory Applications Timothy A. Morgan, ZhaoquanZeng, Greg Salamo Motivation & Approach 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. SubstrateSelection & 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. • 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 • XPS results of dot sample confirm BTO formed • Future • Investigate MgO surface characteristics that are optimal for BTO dot formation • Investigate LAO substrates for dot growth further • Optimize growth conditions for consistent dot formation YAlO3 (220) LaAlO3 (110) BaTiO3 Oxide Substrate Tensile 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 • Shuttered RHEED Technique • Perovskite structure (ABO3) • Alternating layers of AO & BO2 Obtainining an atomically flat surface on our substrate is our goal. We have worked on preparing MgO through annealing with oxygen flow. MgO @ 850° C 12 hrs • 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)