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Patterning metal contacts on monolayer MoS2 with vanishing Schottky barriers using thermal nanolithography

Nature Electronics volume 2, pages 17–25 (2019)Cite this article

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Abstract

Two-dimensional semiconductors, such as molybdenum disulfide (MoS2), exhibit a variety of properties that could be useful in the development of novel electronic devices. However, nanopatterning metal electrodes on such atomic layers, which is typically achieved using electron beam lithography, is currently problematic, leading to non-ohmic contacts and high Schottky barriers. Here, we show that thermal scanning probe lithography can be used to pattern metal electrodes with high reproducibility, sub-10-nm resolution, and high throughput (105 μm2 h−1 per single probe). The approach, which offers simultaneous in situ imaging and patterning, does not require a vacuum, high energy, or charged beams, in contrast to electron beam lithography. Using this technique, we pattern metal electrodes in direct contact with monolayer MoS2 for top-gate and back-gate field-effect transistors. These devices exhibit vanishing Schottky barrier heights (around 0 meV), on/off ratios of 1010, no hysteresis, and subthreshold swings as low as 64 mV per decade without using negative capacitors or hetero-stacks.

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Fig. 1: The t-SPL fabrication process.
Fig. 2: Aligned top-gate FETs on exfoliated 1L MoS2 flakes patterned by t-SPL.
Fig. 3: Back-gate FETs fabricated via t-SPL on exfoliated 1L MoS2 flakes.
Fig. 4: Schottky barrier height characterization of t-SPL FETs on exfoliated 1L MoS2.
Fig. 5: Comparison of t-SPL MoS2 FET performances with literature values.

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The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

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Acknowledgements

The authors acknowledge support from the US Army Research Office (proposal number 69180-CH), the Office of Basic Energy Sciences of the US Department of Energy, the National Science Foundation, SwissLitho, and the European Union’s Horizon 2020 research and innovation programme under grant agreement number 705326 (project SWING). A.S.M.A. and D.S. acknowledge financial support from NSF-ECCS (grant number 1638598).

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  1. These authors contributed equally: Xiaorui Zheng, Annalisa Calò.

Authors and Affiliations

  1. Advanced Science Research Center (ASRC), CUNY Graduate Center, New York, NY, USA

    Xiaorui Zheng, Annalisa Calò, Edoardo Albisetti, Xiangyu Liu & Elisa Riedo

  2. Tandon School of Engineering, New York University, New York, NY, USA

    Xiaorui Zheng, Annalisa Calò, Edoardo Albisetti, Xiangyu Liu, Abdullah Sanad M. Alharbi, Davood Shahrjerdi & Elisa Riedo

  3. Dipartimento di Fisica, Politecnico di Milano, Milano, Italy

    Edoardo Albisetti

  4. Department of Mechanical Engineering, Columbia University, New York, NY, USA

    Ghidewon Arefe & James Hone

  5. SKKU Advanced Institute of Nano-Technology (SAINT), Sungkyunkwan University, Seobu-ro, Jangan-gu, Suwon, Korea

    Xiaochi Liu & Won Jong Yoo

  6. SwissLitho AG Technoparkstrasse 1, Zurich, Switzerland

    Martin Spieser

  7. National Institute of Materials Science, 1-1 Namiki, Tsukuba, Japan

    Takashi Taniguchi & Kenji Watanabe

  8. National Research Council (CNR-SPIN), Rome, Italy

    Carmela Aruta

  9. Electrical Engineering Institute, and Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

    Alberto Ciarrocchi & Andras Kis

  10. Department of Electrical Engineering, Columbia University, New York, NY, USA

    Brian S. Lee & Michal Lipson

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Contributions

X.Z., A.C., E.A. and X.L. patterned the metal electrodes by t-SPL. A.S.M.A. performed the electronic measurements on the t-SPL FETs. X.Z., E.A., X.L., A.S.M.A., D.S. and E.R. designed the electronic experiments and analysed the data on the t-SPL FETs. G.A. and X.L. fabricated and measured the EBL FETs. X.Z., M.S. and E.R. developed the two-polymer stack t-SPL method. W.J.Y. and J.H. designed and analysed the EBL data. T.T. and K.W. provided the h-BN samples. C.A. analysed the XPS data. A.C. and A.K. provided the WSe2 samples and contributed to the corresponding data analysis. B.S.L. and M.L. deposited Pd electrodes on t-SPL FETs. E.R. conceived and analysed all the experiments on t-SPL FETs. X.Z., A.C., E.A., G.A., J.H., D.S. and E.R. contributed to writing the article.

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Correspondence to Edoardo Albisetti or Elisa Riedo.

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Supplementary information

Supplementary Information

Supplementary Sections 1–15, Supplementary Figures 1–24, and Supplementary Tables 1–3.

Supplementary Video 1

Real-time screenshot recording acquired during the patterning process on PPA, from the writing of the large pads (10 × 10 µm2 squares) to the small fingers (1.5 µm wide) lying on top of a monolayer CVD MoS2 flake. The number of frames is 81,258 (29 frames per second).

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Zheng, X., Calò, A., Albisetti, E. et al. Patterning metal contacts on monolayer MoS2 with vanishing Schottky barriers using thermal nanolithography. Nat Electron 2, 17–25 (2019). https://doi.org/10.1038/s41928-018-0191-0

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