Influence of Copper on the Switching Properties of Hafnium Oxide-Based Resistive Memory
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Influence of Copper on the Switching Properties of Hafnium Oxide-Based Resistive Memory B.D. Briggs1, S.M. Bishop1, K.D. Leedy2, B. Butcher1, R. L. Moore1, S. W. Novak1, and N.C. Cady1 1
University at Albany, SUNY, College of Nanoscale Science and Engineering, Albany, NY 12203, U.S.A. 2 Air Force Research Laboratory, 2241 Avionics Circle, Dayton, OH, 45433, U.S.A.
ABSTRACT Hafnium oxide-based resistive memory devices have been fabricated on copper bottom electrodes. The HfOx active layers in these devices were deposited by atomic layer deposition at 250 °C with tetrakis(dimethylamido)hafnium(IV) as the metal precursor and an O2 plasma as the reactant. Depth profiles of the HfOx by x-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a copper concentration on the order of five atomic percent throughout the HfOx film. This phenomenon has not been previously reported in resistive switching literature and therefore may have gone unnoticed by other investigators. The MIM structures fabricated from the HfOx exhibited non-polar behavior, independent of the top metal electrode (Ni, Pt, Al, Au). These results are analogous to the non-polar switching behavior observed by Yang et al. [2] for intentionally Cu-doped HfOx resistive memory devices. The distinguishing characteristic of the material structure produced in this research is that the copper concentration increases to 60 % in a conducting surface copper oxide layer ~20 nm thick. Lastly, the results from both sweep- and pulse-mode current-voltage measurements are presented and preliminary work on fabricating sub-100 nm devices is summarized. INTRODUCTION Transition metal oxide resistive memory devices are a leading candidate for next generation non-volatile storage. When compared to current CMOS NAND flash, resistive memory has the potential to offer lower power operation, increased density through a simpler fabrication process and ultimately, faster operation. Hafnium oxide has been selected as the transition metal oxide for this work due to its large band gap (5.8 eV), the resulting low off-state leakage current, and its wide spread use in CMOS manufacturing as a high-k gate dielectric. Hafnium oxide has been previously studied as the active layer in resistive memory devices by multiple groups. These investigations have demonstrated devices with stable, long-term read/write endurance [1-3], low switching energy [4], and high on/off ratios [2]. Previous work has shown the effects of Cu on the performance of HfOx based resistive memory, by the insertion of a Cu layer between the HfOx used to intentionally dope the HfOx [2] or using Cu as a top electrode as a reservoir of metallic ions, thought to form conductive filaments during switching [3]. Of particular interest to our work is the role of copper doping in HfO2 films created by atomic layer deposition on copper.
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EXPERIMENTAL PROCEDURE A starting substrate of SiO2/SiN was fabricated on 300mm silicon wafers using standard chemical vapor deposition techniques. Atop the substrate, Cu/Ta/TaN
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