Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016 Sep 2:6:32614.
doi: 10.1038/srep32614.

High Density Crossbar Arrays with Sub- 15 nm Single Cells via Liftoff Process Only

Ali Khiat  1   2 , Peter Ayliffe  2 , Themistoklis Prodromakis  1   2
Affiliations

High Density Crossbar Arrays with Sub- 15 nm Single Cells via Liftoff Process Only

Ali Khiat et al. Sci Rep. .

Abstract

Emerging nano-scale technologies are pushing the fabrication boundaries at their limits, for leveraging an even higher density of nano-devices towards reaching 4F(2)/cell footprint in 3D arrays. Here, we study the liftoff process limits to achieve extreme dense nanowires while ensuring preservation of thin film quality. The proposed method is optimized for attaining a multiple layer fabrication to reliably achieve 3D nano-device stacks of 32 × 32 nanowire arrays across 6-inch wafer, using electron beam lithography at 100 kV and polymethyl methacrylate (PMMA) resist at different thicknesses. The resist thickness and its geometric profile after development were identified to be the major limiting factors, and suggestions for addressing these issues are provided. Multiple layers were successfully achieved to fabricate arrays of 1 Ki cells that have sub- 15 nm nanowires distant by 28 nm across 6-inch wafer.

PubMed Disclaimer

Figures

Figure 1
Figure 1. Main fabrication steps of dense nano-scale array of RRAM devices.
(a) E-beam bottom electrodes, (b) bottom access-electrodes, (c) TiO2−x active layer, (d) e-beam top electrodes, (e) top access-electrodes, (f) 32 × 32 ACnWs, (g) schematic representation of a single RRAM cell.
Figure 2
Figure 2
SEM images of (a) SCnWs with 70 nm widths, and (b,c) show zoom-in images of the corresponding areas. (d) ACnWs with widths and gaps of 70 nm, (e,f) show zoom-in images of the corresponding areas.
Figure 3
Figure 3. Reducing the features’ sizes.
Single cross-point nanowires (SCnW): (a) 15 nm, (b) 25 nm, (c) 28 nm and (d) 32 nm with the insets depicting the crossbars, scale bars are 1 μm. Array of cross-point nanowires (ACnW) at 100 nm pitches: (e) 15 nm, (f) 25 nm, (g) 28 nm and (h) 32 nm, scale bars are 100 nm.
Figure 4
Figure 4. Resist limitations. Influence of the resist on the liftoff quality of 10 nm Ti.
(a) PMMA495/MMA (150/250 nm), (b) PMMA950 (130 nm), (c) PMMA950:ZEP A (50 nm), (d) PMMA950:ZEP A (40 nm), (e) PMMA950:ZEP A (30 nm) and (f) PMMA950:ZEP A (15 nm). Influence of the exposure gaps in PMMA950:ZEP A (1:1.5) resist on the nanowire density; (g) 45 nm, (h) 30 nm and (i) 20 nm gaps.
Figure 5
Figure 5. The optimum array cross-points devices with the smallest, densest and thickest metal nanowires.
(a) 32 × 32 wires with 15 nm widths and 22 nm gaps (close-up image in b), (c) 32 × 32 wires with 15 nm widths and 28 nm gaps (close-up image in d).
See this image and copyright information in PMC

References

    1. Zhong Z., Wang D., Cui Y., Bockrath M. W. & Lieber C. M. Nanowire Crossbar Arrays as Address Decoders for Integrated Nanosystems. Science (80-). 302, 1377–1379 (2003). - PubMed
    1. Chua L. O. Memristor-The Missing Circuit Element. IEEE Trans. Circuit Theory Ct-18, 507–519 (1971).
    1. Strukov D. B., Snider G. S., Stewart D. R. & Williams R. S. The missing memristor found. Nature 453, 80–83 (2008). - PubMed
    1. Chen W. & Ahmed H. Fabrication of 5–7 nm wide etched lines in silicon using 100 keV electron-beam lithography and polymethylmethacrylate resist. Appl. Phys. Lett. 62, 1499–1501 (1993).
    1. Yasin S., Hasko D. G. & Ahmed H. Fabrication of <5 nm width lines in poly(methylmethacrylate) resist using a water:isopropyl alcohol developer and ultrasonically-assisted development. Appl. Phys. Lett. 78, 2760–2762 (2001).

Publication types