| AVS 58th Annual International Symposium and Exhibition | |
| Advanced Surface Engineering Division | Thursday Sessions |
| Session SE-ThM |
| Session: | Nanostructured Thin Films and Coatings |
| Presenter: | J.L. Tedesco, National Institute of Standards and Technology |
| Authors: | J.L. Tedesco, National Institute of Standards and Technology W. Zheng, National Institute of Standards and Technology O.A. Kirillov, National Institute of Standards and Technology S. Pookpanratana, National Institute of Standards and Technology A.A. Herzing, National Institute of Standards and Technology H.-J. Jang, National Institute of Standards and Technology P.P. Kavuri, National Institute of Standards and Technology N.V. Nguyen, National Institute of Standards and Technology C.A. Richter, National Institute of Standards and Technology |
| Correspondent: | Click to Email |
Memristors, nonvolatile bipolar resistive switching devices first intentionally fabricated in 2008 [1], have attracted attention for use in a wide range of applications. To date, most memristors have been fabricated from either TiOx [1] or TaOx [2]. However, it is necessary to explore other dielectric materials, because the memristive properties of these dielectrics have not yet been explored.
In this study, memristors were fabricated on both silicon and flexible polyethylene teraphthalate (PET) substrates by using HfO2, HfSiO4, and ZrSiO4 thin films and thermally evaporated aluminum contacts. The dielectric films were formed from sol-gel precursors synthesized based on the recipe of Meena et al. [3]. Following synthesis, the precursors were spun on to substrates, exposed to an oxygen plasma, and annealed in air at 150°C for 24 hours. Memristors with cross sectional areas ranging from 2×2 mm2 to 0.5×0.5 mm2 were fabricated.
The dielectric films were extensively characterized by using optical profilometry and microscopy, x-ray photoelectron spectroscopy (XPS), and deep ultraviolet spectroscopic ellipsometry (SE). The optical profilometry measurements demonstrate that the films show no evidence of significant inhomogeneities due to the solvent-based sol-gel synthesis methods. According to the XPS measurements, the films are ≈50% carbon. Such high levels of carbon are reasonable given the synthesis approach employed, and similarly high levels of carbon have been observed previously in TiO2 films synthesized from sol-gels [4]. From the SE measurements, it is evident that the bandgaps of the HfO2, HfSiO4, and ZrSiO4 films are similar to their predicted values, but the densities of the films are ≈0.5 due to the high amounts of excess carbon. Transmission electron microscopy measurements of the films will also be discussed.
Current-voltage (I-V), capacitance-voltage (C-V), capacitance-frequency (C-f), and conductance-frequency (G-f) measurements were performed at room temperature in a commercial probe station. The I‑V measurements indicate that devices fabricated from these films exhibit bipolar resistive switching. Furthermore, optical microscopy images indicate that the switching events are often accompanied by significant changes to the morphology of the active region of the device, particularly when the switching occurs at high voltages. These changes suggest the formation of localized conduction pathways through the dielectric. The C‑f and G-f measurements indicate that the capacitive properties of the devices also change following switching events. Additionally, after 24 days, retention tests show the devices are still in the ON state, thus, they may be considered nonvolatile.
References
[1] D.B. Strukov et al., Nature 438, 80 (2008).
[2] J.J. Yang et al., Appl. Phys. Lett. 97, 232102 (2010).
[3] J.S. Meena et al., 2010 3rd International Nanoelectronics Conference (INEC), 1-2, 992, 2010.
[4] J.L. Tedesco et al., ECS Trans. 35, 107 (2011).