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

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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

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.

Data availability

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

References

  1. 1.

    Allain, A., Kang, J., Banerjee, K. & Kis, A. Electrical contacts to two-dimensional semiconductors. Nat. Mater. 14, 1195–1205 (2015).

    Article  Google Scholar 

  2. 2.

    Garcia, R., Knoll, A. W. & Riedo, E. Advanced scanning probe lithography. Nat. Nanotech. 9, 577–587 (2014).

    Article  Google Scholar 

  3. 3.

    Desai, S. B. et al. MoS2 transistors with 1-nanometer gate lengths. Science 354, 99–102 (2016).

    Article  Google Scholar 

  4. 4.

    Radisavljevic, B., Radenovic, A., Brivio, J., Giacometti, V. & Kis, A. Single-layer MoS2 transistors. Nat. Nanotech. 6, 147–150 (2011).

    Article  Google Scholar 

  5. 5.

    Chhowalla, M., Jena, D. & Zhang, H. Two-dimensional semiconductors for transistors. Nat. Rev. Mater. 1, 1–15 (2016).

    Article  Google Scholar 

  6. 6.

    Lembke, D., Bertolazzi, S. & Kis, A. Single-layer MoS2 electronics. Acc. Chem. Res. 48, 100–110 (2015).

    Article  Google Scholar 

  7. 7.

    Xu, Y. et al. Contacts between two- and three-dimensional materials: ohmic, Schottky, and p–n heterojunctions. ACS Nano 10, 4895–4919 (2016).

    Article  Google Scholar 

  8. 8.

    Zhao, Y. et al. Doping, contact and interface engineering of two-dimensional layered transition metal dichalcogenides transistors. Adv. Funct. Mater. 27, 1603484 (2017).

    Article  Google Scholar 

  9. 9.

    Wang, W. et al. Controllable Schottky barriers between MoS2 and Permalloy. Sci. Rep. 4, 6928 (2014).

    Article  Google Scholar 

  10. 10.

    Yang, L. et al. Chloride molecular doping technique on 2D materials: WS2 and MoS2. Nano Lett. 14, 6275–6280 (2014).

    Article  Google Scholar 

  11. 11.

    Kappera, R. et al. Phase-engineered low-resistance contacts for ultrathin MoS2 transistors. Nat. Mater. 13, 1128–1134 (2014).

    Article  Google Scholar 

  12. 12.

    Farmanbar, M. & Brocks, G. Controlling the Schottky barrier at MoS2/metal contacts by inserting a BN monolayer. Phys. Rev. B 91, 161304 (2015).

    Article  Google Scholar 

  13. 13.

    Cui, X. et al. Multi-terminal transport measurements of MoS2 using a van der Waals heterostructure device platform. Nat. Nanotech. 10, 534–540 (2015).

    Article  Google Scholar 

  14. 14.

    Guimarães, M. H. et al. Atomically thin ohmic edge contacts between two-dimensional materials. ACS Nano 10, 6392–6399 (2016).

    Article  Google Scholar 

  15. 15.

    Leong et al. Low resistance metal contacts to MoS2 devices with nickel etched graphene electrodes. ACS Nano 9, 869–877 (2015).

    Article  Google Scholar 

  16. 16.

    Zan, R. et al. Control of radiation damage in MoS2 by graphene encapsulation. ACS Nano 7, 10167–10174 (2013).

    Article  Google Scholar 

  17. 17.

    Meyer, J. C. et al. Accurate measurement of electron beam induced displacement cross sections for single-layer graphene. Phys. Rev. Lett. 108, 196102 (2012).

    Article  Google Scholar 

  18. 18.

    Lehnert, T., Lehtinen, O., Algara–Siller, G. & Kaiser, U. Electron radiation damage mechanisms in 2D MoSe2. Appl. Phys. Lett. 110, 033106 (2017).

    Article  Google Scholar 

  19. 19.

    Imamura, G. & Saiki, K. Modification of graphene/SiO2 interface by UV-irradiation: effect on electrical characteristics. ACS Appl. Mater. Interfaces 7, 2439–2443 (2015).

    Article  Google Scholar 

  20. 20.

    Zhang, R., Chen, T., Bunting, A. & Cheung, R. Optical lithography technique for the fabrication of devices from mechanically exfoliated two-dimensional materials. Microelectron. Eng. 154, 62–68 (2016).

    Article  Google Scholar 

  21. 21.

    Ishigami, M., Chen, J. H., Cullen, W. G., Fuhrer, M. S. & Williams, E. D. Atomic structure of graphene on SiO2. Nano Lett. 7, 1643–1648 (2007).

    Article  Google Scholar 

  22. 22.

    Robinson, J. A. et al. Contacting graphene. Appl. Phys. Lett. 98, 053103 (2011).

    Article  Google Scholar 

  23. 23.

    Macintyre, D. S., Ignatova, O., Thoms, S. & Thayne, I. G. Resist residues and transistor gate fabrication. J. Vac. Sci. Technol. B 27, 2597–2601 (2009).

    Article  Google Scholar 

  24. 24.

    Kang, S., Movva, H. C. P., Sanne, A., Rai, A. & Banerjee, S. K. Influence of electron-beam lithography exposure current level on the transport characteristics of graphene field effect transistors. J. Appl. Phys. 119, 124502 (2016).

    Article  Google Scholar 

  25. 25.

    Lin, Y. C. et al. Graphene annealing: how clean can it be? Nano Lett. 12, 414–419 (2012).

    Article  Google Scholar 

  26. 26.

    Van Ngoc, H., Qian, Y., Han, S. K. & Kang, D. J. PMMA-etching-free transfer of wafer-scale chemical vapor deposition two-dimensional atomic crystal by a water soluble polyvinyl alcohol polymer method. Sci. Rep. 6, 33096 (2016).

    Article  Google Scholar 

  27. 27.

    Lin, Z. et al. Controllable growth of large-size crystalline MoS2 and resist-free transfer assisted with a Cu thin film. Sci. Rep. 5, 18596 (2015).

    Article  Google Scholar 

  28. 28.

    Albisetti, E. et al. Nanopatterning reconfigurable magnetic landscapes via thermally assisted scanning probe lithography. Nat. Nanotech. 11, 545–551 (2016).

    Article  Google Scholar 

  29. 29.

    Pires, D. et al. Nanoscale three-dimensional patterning of molecular resists by scanning probes. Science 328, 732–735 (2010).

    Article  Google Scholar 

  30. 30.

    Carroll, K. M. et al. Parallelization of thermochemical nanolithography. Nanoscale 6, 1299–1304 (2014).

    Article  Google Scholar 

  31. 31.

    Szoszkiewicz, R. et al. High-speed, sub-15 nm feature size thermochemical nanolithography. Nano Lett. 7, 1064–1069 (2007).

    Article  Google Scholar 

  32. 32.

    Wu, W. et al. High mobility and high on/off ratio field-effect transistors based on chemical vapor deposited single-crystal MoS2 grains. Appl. Phys. Lett. 102, 142106 (2013).

    Article  Google Scholar 

  33. 33.

    Kim, C. et al. Fermi level pinning at electrical metal contacts of monolayer molybdenum dichalcogenides. ACS Nano 11, 1588–1596 (2017).

    Article  Google Scholar 

  34. 34.

    Chen, J. R. et al. Control of Schottky barriers in single layer MoS2 transistors with ferromagnetic contacts. Nano Lett. 13, 3106–3110 (2013).

    Article  Google Scholar 

  35. 35.

    Kwon, J. et al. Thickness-dependent Schottky barrier height of MoS2 field-effect transistors. Nanoscale 9, 6151–6157 (2017).

    Article  Google Scholar 

  36. 36.

    Cui, X. et al. Low-temperature ohmic contact to monolayer MoS2by van der Waals bonded Co/h-BN electrodes. Nano Lett. 17, 4781–4786 (2017).

    Article  Google Scholar 

  37. 37.

    Ryu Cho, Y. K. et al. Sub-10 nanometer feature size in silicon using thermal scanning probe lithography. ACS Nano 11, 11890–11897 (2017).

    Article  Google Scholar 

  38. 38.

    Gottlieb, S. et al. Thermal scanning probe lithography for the directed self-assembly of block copolymers. Nanotechnology 28, 175301 (2017).

    Article  Google Scholar 

  39. 39.

    Lee, C. et al. Anomalous lattice vibrations of single and few-layer MoS2. ACS Nano 4, 2695–2700 (2010).

    Article  Google Scholar 

  40. 40.

    Castellanos-Gomez, A. et al. Laser-thinning of MoS2: on demand generation of a single-layer semiconductor. Nano Lett. 12, 3187–3192 (2012).

    Article  Google Scholar 

  41. 41.

    Li, H. et al. From bulk to monolayer MoS2: evolution of Raman scattering. Adv. Funct. Mater. 22, 1385–1390 (2012).

    Article  Google Scholar 

  42. 42.

    Liu, W., Sarkar, D., Kang, J., Cao, W. & Banerjee, K. Impact of contact on the operation and performance of back-gated monolayer MoS2 field-effect-transistors. ACS Nano 9, 7904–7912 (2015).

    Article  Google Scholar 

  43. 43.

    Childres, I. et al. Effect of electron-beam irradiation on graphene field effect devices. Appl. Phys. Lett. 97, 173109 (2010).

    Article  Google Scholar 

  44. 44.

    Parkin, W. M. et al. Raman shifts in electron-irradiated monolayer MoS2. ACS Nano 10, 4134–4142 (2016).

    Article  Google Scholar 

  45. 45.

    Ji, H. et al. Thickness-dependent carrier mobility of ambipolar MoTe2: Interplay between interface trap and Coulomb scattering. App. Phys. Lett. 110, 183501 (2017).

    Article  Google Scholar 

  46. 46.

    Das, S., Chen, H. Y., Penumatcha, A. V. & Appenzeller, J. High performance multilayer MoS2 transistors with scandium contacts. Nano Lett. 13, 100–105 (2013).

    Article  Google Scholar 

  47. 47.

    Popov, I., Seifert, G. & Tomanek, D. Designing electrical contacts to MoS2 monolayers: a computational study. Phys. Rev. Lett. 108, 156802 (2012).

    Article  Google Scholar 

  48. 48.

    Su, J., Feng, L., Zhang, Y. & Liu, Z. Defect induced gap states in monolayer MoS2 control the Schottky barriers of Pt-mMoS2 interfaces. Appl. Phys. Lett. 110, 161604 (2017).

    Article  Google Scholar 

  49. 49.

    Liu, Y., Stradins, P. & Wei, S.-H. Van der Waals metal–semiconductor junction: weak Fermi level pinning enables effective tuning of Schottky barrier. Sci. Adv. 2, 1–6 (2016).

    Google Scholar 

  50. 50.

    Mott, N. F. Metal–insulator transition. Rev Mod Phys 40, 677–683 (1968).

    Article  Google Scholar 

  51. 51.

    Radisavljevic, B. & Kis, A. Mobility engineering and a metal–insulator transition in monolayer MoS2. Nat. Mater. 12, 815–820 (2013).

    Article  Google Scholar 

  52. 52.

    Schmidt, H. et al. Transport properties of monolayer MoS2 grown by chemical vapor deposition. Nano Lett. 14, 1909–1913 (2014).

    Article  Google Scholar 

  53. 53.

    Wang, J. et al. High mobility MoS2 transistor with low Schottky barrier contact by using atomic thick h-BN as a tunneling layer. Adv. Mater. 28, 8302–8308 (2016).

    Article  Google Scholar 

  54. 54.

    Li, S.-L. et al. Thickness scaling effect on interfacial barrier and electrical contact to two-dimensional MoS2 layers. ACS Nano 8, 12836–12842 (2014).

    Article  Google Scholar 

  55. 55.

    Tung, R. T. The physics and chemistry of the Schottky barrier height. Appl. Phys. Rev. 1, 011304 (2014).

    Article  Google Scholar 

  56. 56.

    Liu, H. et al. Switching mechanism in single-layer molybdenum disulfide transistors: an insight into current flow across Schottky barriers. ACS Nano 8, 1031–1038 (2014).

    Article  Google Scholar 

  57. 57.

    Baugher, B. W., Churchill, H. O., Yang, Y. & Jarillo-Herrero, P. Intrinsic electronic transport properties of high-quality monolayer and bilayer MoS2. Nano Lett. 13, 4212–4216 (2013).

    Article  Google Scholar 

  58. 58.

    English, C. D., Shine, G., Dorgan, V. E., Saraswat, K. C. & Pop, E. Improved contacts to MoS2 transistors by ultra-high vacuum metal deposition. Nano Lett. 16, 3824–3830 (2016).

    Article  Google Scholar 

  59. 59.

    Dai, Z., Wang, Z., He, X., Zhang, X.-X. & Alshareef, H. N. Large-area chemical vapor deposited MoS2 with transparent conducting oxide contacts toward fully transparent 2D electronics. Adv. Funct. Mater. 27, 1703119 (2017).

    Article  Google Scholar 

  60. 60.

    Si, M. et al. Steep-slope hysteresis-free negative capacitance MoS2 transistors. Nat. Nanotech. 13, 24–28 (2018).

    Article  Google Scholar 

  61. 61.

    Radisavljevic, B., Whitwick, M. B. & Kis, A. Integrated circuits and logic operations based on single-layer MoS2. ACS Nano 5, 9934–9938 (2011).

    Article  Google Scholar 

  62. 62.

    Zhu, Y. et al. Monolayer molybdenum disulfide transistors with single-atom-thick gates. Nano Lett. 18, 3807–3813 (2018).

    Article  Google Scholar 

  63. 63.

    Xie, L. et al. Graphene-contacted ultrashort channel monolayer MoS2 transistors. Adv. Mater. 29, 1702522 (2017).

    Article  Google Scholar 

  64. 64.

    Lembke, D. & Kis, A. Breakdown of high-performance monolayer MoS2 transistors. ACS Nano 6, 10070–10075 (2012).

    Article  Google Scholar 

  65. 65.

    Kang, K. et al. High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity. Nature 520, 656–660 (2015).

    Article  Google Scholar 

  66. 66.

    Rawlings, C., Duerig, U., Hedrick, J., Coady, D. & Knoll, A. Nanometer control of the markerless overlay process using thermal scanning probe lithography. In IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM) 1670–1675 (IEEE, 2014).

Download references

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).

Author information

Affiliations

Authors

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.

Corresponding authors

Correspondence to Edoardo Albisetti or Elisa Riedo.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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).

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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

Download citation

Further reading

Search

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing