Properties of Atomic Layer Deposited Nanolaminates of Zirconium and Cobalt Oxides

Abstract

Five-layer crystalline thin film structures were formed, consisting of ZrO 2 and Co 3 O 4 alternately grown on Si(100) substrates by atomic layer deposition at 300 • C using ZrCl 4 and Co(acac) 3 as the metal precursors and ozone as the oxygen precursor. The performance of the laminate films was dependent on the relative content of constituent oxide layers. The magnetization in these films was nonlinear, saturative, and with very weak coercive fields. Electrical measurements revealed the formation of significant polarization versus external field loops and implied some tendency toward memristive behavior. 59 have so far been quite scarce. In the earlier study devoted to ZrO 2 -Co 3 O 4 nanocomposites grown by ALD using the same chemistry based on cobalt acetylacetonate, zirconium tetrachloride and ozone, 59 the deposition process for cobalt oxide was investigated and established, determining suitable evaporation temperature for Co(acac) 3 precursor, as well as by recording linear relationship between growing mass and the amount of deposition cycles. Using the suitable deposition parameters, ALD growth of ZrO 2 /Co 3 O 4 double layers was demonstrated, together with their performance as dielectric and magnetic materials.In connection with the demand for materials, which could be applied in novel memories because of their advanced magnetic and electric properties, this study was devoted to the description of ZrO 2 -Co 3 O 4 nanolaminates, grown by ALD using ZrCl 4 and Co(acac) 3 as the metal precursors and ozone as the oxygen precursor. Elemental and phase composition, thickness, surface morphology and the polarization characteristics of the samples in the presence of an external magnetic or electric field were determined. In addition, the z E-mail: helina.seemen@ut.ee resistive switching and other electrical characteristics of ZrO 2 -Co 3 O 4 nanolaminates were studied to evaluate whether such films can imply a tendency toward memristive behavior. ExperimentalThe film growth experiments were carried out in a flow-type inhouse built hot-wall ALD reactor 60 at 300 ± 2 • C using ZrCl 4 (99.99%, Sigma Aldrich) and Co(acac) 3 (99.9%, Volatec Ltd.) [acac = tris(2,4-pentanedionato)] as the metal precursors, O 3 as the oxygen precursor and N 2 (99.999%, AGA) as the carrier and purge gas. The ZrCl 4 and Co(acac) 3 were evaporated at 160 ± 2• C and 120 ± 2 • C, respectively, from open boats inside the reactor and transported to the substrates by the carrier gas flow. O 3 was generated from O 2 (99.999%, AGA, Linde Group) in a BMT Messtechnik 802 N ozone generator. The O 3 concentration output of the generator measured with BMT Masstechnik 964 analyzer was ∼262 g/m 3 at the normal pressure. During the deposition, the chamber pressure varied in the range of 205-260 Pa. In all cases, a single ALD cycle was started with a metal precursor pulse and continued with a purge of the reaction zone with the pure carrier gas, oxygen precursor pulse and another purge. The precursor pulse durations and purge lengths in the case of ZrO 2 ...