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Targeted synthesis of polycrystalline vanadium dioxide thin films via post-deposition annealing

Kirill Trunov, Yuri Lebedinskii, Ilya Zavidovskiy, Sergey Novikov, Alexander Morozov, Petr Shvets, Ksenia Maksimova, Andrei Zenkevich, Anton Khanas

Abstract

Implementation of neuromorphic hardware is a promising way to improve the computing efficiency and decrease the energy consumption of artificial neural networks. For this purpose, electronic elements emulating the behavior of synapses and neurons have to be developed. In order to realize electronic artificial neurons, threshold resistive switches or memristors can be efficiently used. One of the most widespread materials for threshold switches is vanadium dioxide due to its property to demonstrate the metal-insulator transition at a temperature about 70 °C. However, the processes of VO$_{2}$ synthesis are quite restrictive in temperature and gas atmosphere conditions, which hinders its integration into CMOS fabrication. In this work, we propose a new method of VO$_{2}$ synthesis: reactive pulsed laser deposition from metallic V target in oxygen atmosphere at room temperature, followed by vacuum annealing. Our method enables target synthesis of an appropriate VO$_{2}$ phase in a polycrystalline thin film form by finely tuning oxygen pressure during room temperature deposition, which allows to relax the equipment demands, such as high temperature heating in oxygen. Successful targeted VO$_{2}$ synthesis under fabrication conditions close to back-end-of-line CMOS production, achieved in this work, show the way toward its large-scale microelectronic integration for neuromorphic hardware creation.

Targeted synthesis of polycrystalline vanadium dioxide thin films via post-deposition annealing

Abstract

Implementation of neuromorphic hardware is a promising way to improve the computing efficiency and decrease the energy consumption of artificial neural networks. For this purpose, electronic elements emulating the behavior of synapses and neurons have to be developed. In order to realize electronic artificial neurons, threshold resistive switches or memristors can be efficiently used. One of the most widespread materials for threshold switches is vanadium dioxide due to its property to demonstrate the metal-insulator transition at a temperature about 70 °C. However, the processes of VO synthesis are quite restrictive in temperature and gas atmosphere conditions, which hinders its integration into CMOS fabrication. In this work, we propose a new method of VO synthesis: reactive pulsed laser deposition from metallic V target in oxygen atmosphere at room temperature, followed by vacuum annealing. Our method enables target synthesis of an appropriate VO phase in a polycrystalline thin film form by finely tuning oxygen pressure during room temperature deposition, which allows to relax the equipment demands, such as high temperature heating in oxygen. Successful targeted VO synthesis under fabrication conditions close to back-end-of-line CMOS production, achieved in this work, show the way toward its large-scale microelectronic integration for neuromorphic hardware creation.

Paper Structure

This paper contains 7 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Experimental methods
  3. Results and discussion
  4. Annealing-induced reduction and crystallization of amorphous VO$_x$ films
  5. Oxygen pressure optimization
  6. VO$_2$ film electrical properties
  7. Conclusion

Figures (4)

  • Figure 1: X-ray photoelectron spectra of a VO$_x$ film after RT deposition (a) and after in situ vacuum annealing at 500$~^\circ$C (b). Both measurements were performed at RT.
  • Figure 2: a) Schematic of reactive PLD of amorphous VO$_x$ film and subsequent vacuum annealing at 490$~^\circ$C. b) Phase composition of VO$_x$ samples as a function of oxygen pressure during deposition. Phase content in the films was established qualitatively using XRD and Raman spectroscopy. Optimal parameters region for VO$_2$ synthesis is highlighted with a red ellipse.
  • Figure 3: a) XRD pattern of a sample grown with $1.60~$Pa O$_2$ pressure and attributed to a VO$_2$ phase. b) Raman spectrum of the same film.
  • Figure 4: a) Temperature dependence of resistivity of a VO$_2$ film measured in Van Der Pauw geometry. b) DC $I$$-$$V$ curves of Ru/VO$_2$/Ru lateral device: voltage sweep curves are drawn in blue (blue arrows indicate sweep direction), current sweep curves -- in red. Insets show schematics of the measuring methods and device structures.