Atomic layer deposition of zirconium oxide thin films

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ATOMIC LAYER DEPOSITION FOR EMERGING THIN-FILM MATERIALS AND APPLICATIONS

Atomic layer deposition of zirconium oxide thin films Xin Wang1, Sujan Kumar Ghosh1, Mahyar Afshar-Mohajer1, Hua Zhou2, Yongqiang Liu3, Xiaoxiao Han1, Jiyu Cai4, Min Zou1,a), Xiangbo Meng1,b),c) 1

Department of Mechanical Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA; and Center for Advanced Surface Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA 2 The Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA 3 Department of Mechanical Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA; and Beijing Advanced Innovation Center for Materials Genome Engineering, Center for Green Innovation, Beijing Key Laboratory for Magneto-Photoelectrical Composite and Interface Science, School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China 4 Department of Mechanical Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA a) Address all correspondence to these authors. e-mail: [email protected] b) e-mail: [email protected] c) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs.org/editor-manuscripts/. Received: 12 September 2019; accepted: 9 October 2019

In this work, we studied an atomic layer deposition (ALD) process of ZrO2 with the precursors of tetrakis(dimethylamido)zirconium(IV) and water. We investigated the growth characteristics and mechanism of the ALD ZrO2 in the temperature range of 50–275 °C. Furthermore, the evolutions of film thickness and morphology were studied and discussed. It was found that the growth rate of ZrO2 decreased almost linearly with the increasing temperature from ;1.81 Å/cycle at 50 °C to ;0.8 Å/cycle at 225 °C. Interestingly, it was revealed that the growth of ZrO2 films ceased after a certain number of ALD cycles at a temperature higher than 250 °C. We also verified that the crystallinity of ZrO2 evolved with deposition temperature from amorphous to crystalline phase. In addition, the wettability of ZrO2 films was studied, showing a hydrophobic nature.

Introduction Zirconium oxide (ZrO2) is an attractive material in many applications, like ceramics production and optical devices, because of its excellent thermal, mechanical, optical, electrical, and catalytic properties [1, 2, 3, 4]. ZrO2 has three crystalline structures: monoclinic (below 1170 °C), tetragonal (1170–2370 °C), and cubic (above 2370 °C) [2]. The monoclinic phase remains stable at room temperature, and the monoclinic-to-tetragonal and tetragonal-tocubic phase transitions may occur at about 1200 °C and 2375 °C, respectively [5]. The density of ZrO2 also varies with different crystalline structures, i.e., 5.89, 6.16, and 6.27 g/cm3 for monoclinic, tetragonal, and cubic phases, respectively [3]. To date, ZrO2 thin films have already been prepared by conventional physical vapor deposi