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Investigation of Ferroelectric Nanodots for Memory Applications

Investigation of Ferroelectric Nanodots for Memory Applications. Timothy A. Morgan, Zhaoquan Zeng , Greg Salamo. Motivation & Approach. Substrate Selection & Preparation. Characterization & Results.

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Investigation of Ferroelectric Nanodots for Memory Applications

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  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 understanding 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 nanoscale dots are attractive due to their small size and therefore high memory density based on hysteresis that could result in a “on-chip” hard drive. In addition ferroelectric based memory has advantages in data retention, power reduction and quicker access times. • 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 Our nanoscale ferroelectric dots will be fabricated by self-assembly due to strain built up from a lattice mismatch between the substrate and barium titanate (BTO) deposited by molecular beam epitaxy (MBE). Dots form due to either compressive (negative mismatch) and tensile (positive mismatch) strain as shown below. MgO @ 700° C 12 hrs BTO on MgO MgO @ 850° C 12 hrs MBE growth is accomplished using a Shuttered RHEED Techniquethat produces alternating layers of AO & BO2 which is monitored by diffraction as shown below Obtainining an atomically flat surface on our substrate is our goal. We have worked on preparing MgO through annealing with oxygen flow. • Acknowledgements • Rob Sleezer • David Monk • Morgan Ware • MRSEC MgO @ 1100° C 12 hrs • BTO on MgO Composition analyisis • Ba, Ti & O peaks found on surface • No substrate impurities found STO (100) substrate BaO layer on STO (100) TiO2 layer on STO (100)

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