| AVS 60th International Symposium and Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuM |
| Session: | ALD for Emerging Applications |
| Presenter: | S.-J. Park, Korea Research Institute of Standards and Science (KRISS), Republic of Korea |
| Authors: | S.-J. Park, Korea Research Institute of Standards and Science (KRISS), Republic of Korea J.-P. Lee, Korea Research Institute of Standards and Science (KRISS), Republic of Korea J.S. Jang, Korea Research Institute of Standards and Science (KRISS), Republic of Korea H. Rhu, Korea Research Institute of Standards and Science (KRISS), Republic of Korea H. Yu, Korea Research Institute of Standards and Science (KRISS), Republic of Korea B.Y. You, Korea Research Institute of Standards and Science (KRISS), Republic of Korea C.S. Kim, Korea Research Institute of Standards and Science (KRISS), Republic of Korea K.J. Kim, Korea Research Institute of Standards and Science (KRISS), Republic of Korea Y.-J. Cho, Korea Research Institute of Standards and Science (KRISS), Republic of Korea S. Baik, POSTECH, Republic of Korea W. Lee, Korea Research Institute of Standards and Science (KRISS), Republic of Korea |
| Correspondent: | Click to Email |
TiOx is one of the promising candidates for resistive switching (RS) devices. It has been generally accepted that formation of oxygen deficient Magnéli phase resulting from field-induced migration and ordering of oxygen vacancies (VO) is mainly responsible for the resistive switching (RS) in TiOx-based RS devices [1,2]. In this regard, it is worth studying the effect of oxygen vacancy concentration on the RS behaviors of the memristors adopting TiOx as a switching layer. To this end, Pt/TiOx/Pt capacitors with different values of x were prepared in this study. It has been well established that stoichiometry of TiOx was closely related to the oxygen vacancy concentration [3]. TiOx films were grown by plasma enhanced atomic layer deposition (PEALD) at the substrate temperature of 150 °C. Titanium (IV) tetraisopropoxide (TTIP; Ti[OCH(CH3)2]4) was used as a Ti precursor. High purity oxygen or mixture gas of pure oxygen and nitrogen was adopted as a reactant during the plasma exposure step. By taking advantage of versatile controlling capability of ALD over the film properties, we were able to deliberately control the stoichiometry of TiOx films by adjusting the flow rate ratio (RF) of O2 gas to N2 + O2 mixture gas from 0.25 to 1.00 .
Microstructure and properties of the resulting films were characterized by Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), X-ray diffraction (XRD), confocal Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). According to RBS result, x in TiOx was found to be varied from 1.62 to 1.70 when RF was altered from 0.25 to 1.00. Phases of PEALD TiOx films were observed to be amorphous at RF = 0.25, whereas nanocrystalline anatase at RF = 1.00. Raman spectroscopic analysis provided an additional evidence for RF dependence of the film crystallinity. It turned out from the deconvolution of the O1s XPS peaks that non-lattice oxygen content increases from 15.3 to 20.7% with decreasing the RF from 1.00 to 0.25, which manifests increases of oxygen vacancies in PEALD TiO2 film with RF. It was found from SE analyses that the absorption originated from defect states below bandgap, monotonously increases with decrease of x, i.e., increase of oxygen vacancy. Based on these results, the effect of oxygen vacancy concentration on RS behaviors of TiOx-based memristors will be discussed in detail in this presentation.
References
(1) R. Waser, et al., Adv. Mater.21, 2632 (2009)
(2) D. H. Kwon, et al., Nat. Nanotechnol. 5, 148 (2010)
(3) H. Seo, et al., Nano Lett. 11, 751 (2010)