Response. Investigation of Ferroelectric Nanodots for Memory Applications. Timothy A. Morgan, Zhaoquan Zeng , Greg Salamo. Bias. Motivation & Approach. Substrate Selection & Preparation. Characterization & Results.
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Investigation of Ferroelectric Nanodots for Memory Applications
Timothy A. Morgan, ZhaoquanZeng, Greg Salamo
Motivation & Approach
Substrate Selection & Preparation
Characterization & Results
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.
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.
BTO on YAlO3
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.
MgO @ 1100° C 12 hrs
STO (100) substrate
BaO layer on STO (100)
TiO2 layer on STO (100)