Vanadium Oxide Device with Tunable Oxygen Vacancy Concentration for Neuromorphic Computing
Authors: Finnegan Patrick Sean , Oh Sangheon , Zutter Brian , Bishop Sean R , Christensen Adam Scott , Agarwal Sapan , Fuller Elliot J. , Talin Albert Alec 
Published: December 2024

Analog, non-volatile memories that can enable in-memory data processing are attractive for exploring non-von-Neumann architectures to realize substantially more efficient computing for AI applications. Among the various device concepts, NVMs based on tuning of point defects via insertion of ions such as alkali metals, protons, or oxygen vacancies are attractive due to the ability to finely tune the electronic conductivity by controlling the defect concentration. Previously, oxygen vacancy concentration in vanadium oxide (VO2-x) has been linked to electronic conductivity and the insulator-to-metal transition temperature. However, while previous studies have mainly concentrated on single crystal epitaxial films of VO2, polycrystalline films deposited by technique compatible with Si back end of the line (BEOL) fabrication scheme are considerably easier to integrate with CMOS circuitry. We employ two distinct approaches for device integration of VO2-x thin films: (1) an electron beam evaporation deposition of bulk vanadium (V) precursor followed by annealing in an oxygen (O2) environment, and (2) reactive sputtering of vanadium oxide followed by annealing in air. Raman spectroscopy reveals the presence of VO2 and V2O5 phases, with differing ratios indicative of device conductance states [Figure 1b].1

Previous research has demonstrated that the characteristics of VO2 insulator to metal transition (IMT) can be adjusted by manipulating oxygen vacancy concentration using an electrolyte.2 However, the presence of the electrolyte interface can introduce noise due to uncontrolled parasitic reactions. To mitigate this issue, our study utilized electron beam irradiation to deliberately induce vacancies in the VO2 without relying on an electrolyte. This controlled alteration of the device state was found to lead to a significant change in noise levels, particularly when the device was in proximity to the IMT transition temperature.
The analysis of our films provides detailed structural and compositional dynamics of VO2-x and V2O5 phases which exhibit analog synaptic and threshold tunability with remarkable state retention2
[Figure 1cd]. This abstract provides a comparative analysis of these approaches, focusing on their respective advantages and disadvantages in the context of vanadium oxide based analog device fabrication.
References:

Oh, Xiao, Bennett, Finnegan, Fuller, Agarwal, Talin IEDM 2023

Jeong et al., Science, 20

Zutter, Oh, Fuller, Brown, Anderson, Beltran, Blanco, Lopez-Meza, Bishop, Finnegan, Ievlev, Sugar, Kumar, Fuller, Balbuena, Williams, Talin Nat. Mat. (in review)

Li, Fuller, Talin et al., Adv. Elec. Mat. 2023

Marinella, Bennett, Zutter, Xiao, Fuller, Hughart, Agarwal, Li, Talin IEEE Trans. Nuc. Sci. 2023

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

Figure 1