Research ArticleMATERIALS SCIENCE

Flexible active-matrix organic light-emitting diode display enabled by MoS2 thin-film transistor

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Science Advances  20 Apr 2018:
Vol. 4, no. 4, eaas8721
DOI: 10.1126/sciadv.aas8721
  • Fig. 1 The device structure of flexible OLED display with MoS2-based backplane circuitry.

    (A) Schematic of high-mobility MoS2 TFT using an Al2O3 passivation layer. The Al2O3 passivation layer ensures n-type doping of not only the MoS2 channel region but also the contact region (top); ultrathin AM-OLED display using the high-performance MoS2-based backplane array (middle), which is attached as a display to human skin (bottom). (B) Specific layer structure of the ultrathin AM-OLED display. The thickness of the total display system is less than 7 μm. (C) Optical image of the assembled display on the flexible ultrathin polymer substrate; low bending stiffness of the display offers ultraflexibility. The inset image shows the flat state of the active-matrix display circuit.

  • Fig. 2 The device characteristics of MoS2 TFTs with different structures.

    (A) Transfer characteristics of bilayer MoS2 TFTs with various device structures (in all cases, MoS2 was on top of S/D contacts); [inset shows the top-gated (TG) ③ and ④] back-gated (BG) MoS2 TFT on SiO2/Si (①), back-gated MoS2 TFT on SiO2/Si with Al2O3 encapsulation (②), top-gated MoS2 TFT on SiO2/Si (③), and top-gated MoS2 TFT on Al2O3/SiO2/Si (④). The top-gated MoS2 TFT sandwiched by two Al2O3 layers (④) showed the high performance over other fabricated TFTs. (B) Output characteristics of all TFTs (①, ②, ③, and ④) corresponding to (A); inset shows the increment of current density at shown bias. (C) Mobility values for all TFTs (①, ②, ③, and ④) corresponding to (A). (D) Transfer line plot for extracting line contact resistivity (Rc) and channel sheet resistance (Rsh) under different gating conditions. (E) Extracted Rc (filled circle) and Rsh (empty circle) of back-gated bilayer MoS2 TFTs on Al2O3/SiO2 substrate before (black) and after (red) Al2O3 deposition. (F) Transfer characteristics of top-gated Al2O3/MoS2/Al2O3 sandwiched TFTs (100 devices). Insets show the photograph of wafer-scale fabrication of TFTs and mobility histogram for 500 TFTs showing the average value of mobility (18.1 cm2 V−1 s−1).

  • Fig. 3 The device characteristics of an OLED pixel driven by MoS2 TFT.

    (A) Equivalent circuit diagram (top) and optical image of unit AM-OLED pixel by a single TFT. The single pixel is composed of a transistor and diode for a demonstration of the simplified active-matrix circuitry. (B) Current density and luminance of typical OLED device as a function of applying voltage. (C) Photographic images of ON/OFF switching using gate bias control of MoS2 TFT. (D) Brightness control of unit OLED pixel according to gate bias. Luminance is well distinguishable as a function of the bias, which is stepped from 4 to 9 V (steps, 1 V). (E) Current-voltage (I-V) characteristics of the unit pixel during data voltage sweep from 0 to 10 V with gate bias steps. (F) Plot of pixel switching properties controlled using gate bias repeatedly. OLED is reliably turned ON and OFF using the MoS2 TFT gate signal.

  • Fig. 4 Flexible OLED display driven by MoS2 backplane circuitry.

    (A) Photographic image of ultrathin AM-OLED display on the human wrist while the display is operated; display stably attached to the skin owing to the ultrathin substrate. (B) Current mapping result during the display of the letter “M”; current of ON pixel (green dot) and OFF pixel (black dot), demonstrating uniform and low cross-talk properties. (C) Optical images of dynamic operation on human wrist using the external circuit; representative letters “M,” “O,” “S,” and “2” are sequentially changed on skin according to the active-matrix line addressing. (D) Optical images of the peel-off process from carrier glass substrate. The ultrathin display is folded during peel-off, owing to the low bending stiffness of the total display system.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/eaas8721/DC1

    Supplementary Text

    fig. S1. Atomic force microscopy images of SiO2 and Al2O3/SiO2.

    fig. S2. Cross-sectional transmission electron microscopy image of Al2O3/MoS2/Al2O3 sandwiched structure.

    fig. S3. Optical analysis of MoS2 film on Al2O3 layer.

    fig. S4. Optical analysis of MoS2 film by Al2O3 layer encapsulation.

    fig. S5. Optical analysis of MoS2 film sandwiched with Al2O3 layer.

    fig. S6. Schematic band diagram of Au/MoS2 contacts with and without Al2O3 encapsulation.

    fig. S7. Hysteresis of top-gated bilayer MoS2 TFTs on SiO2/Si substrate (green) and Al2O3/SiO2/Si substrate (blue).

    fig. S8. Statistical data analysis of electrical properties of modified MoS2 TFT.

    fig. S9. Electrical properties of single-crystal MoS2 TFTs.

    fig. S10. Contact and channel sheet resistance analysis of top-gated MoS2 TFT.

    fig. S11. The stability of Al2O3-encapsulated MoS2 TFTs for 1-month period.

    fig. S12. Intrinsic OLED properties and structure information.

    fig. S13. Analysis of current-voltage characteristics of AM-OLED pixel at different gate biases from 4 to 9 V.

    fig. S14. Layout structure of designed active-matrix display.

    fig. S15. Schematic illustration of steps for ultrathin AM-OLED display fabrication.

    fig. S16. Normalized ON current values of unit pixel at the initial bending radius of 0.7 mm repeatedly.

    table S1. The characteristics of MoS2-based TFTs with different device structures.

    movie S1. Active-matrix display operation on human wrist with external circuit.

    movie S2. The dynamic operation of ultrathin display during peeling-off process.

    Reference (36)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. Atomic force microscopy images of SiO2 and Al2O3/SiO2.
    • fig. S2. Cross-sectional transmission electron microscopy image of Al2O3/MoS2/Al2O3 sandwiched structure.
    • fig. S3. Optical analysis of MoS2 film on Al2O3 layer.
    • fig. S4. Optical analysis of MoS2 film by Al2O3 layer encapsulation.
    • fig. S5. Optical analysis of MoS2 film sandwiched with Al2O3 layer.
    • fig. S6. Schematic band diagram of Au/MoS2 contacts with and without Al2O3 encapsulation.
    • fig. S7. Hysteresis of top-gated bilayer MoS2 TFTs on SiO2/Si substrate (green) and Al2O3/SiO2/Si substrate (blue).
    • fig. S8. Statistical data analysis of electrical properties of modified MoS2 TFT.
    • fig. S9. Electrical properties of single-crystal MoS2 TFTs.
    • fig. S10. Contact and channel sheet resistance analysis of top-gated MoS2 TFT.
    • fig. S11. The stability of Al2O3-encapsulated MoS2 TFTs for 1-month period.
    • fig. S12. Intrinsic OLED properties and structure information.
    • fig. S13. Analysis of current-voltage characteristics of AM-OLED pixel at different gate biases from 4 to 9 V.
    • fig. S14. Layout structure of designed active-matrix display.
    • fig. S15. Schematic illustration of steps for ultrathin AM-OLED display fabrication.
    • fig. S16. Normalized ON current values of unit pixel at the initial bending radius of 0.7 mm repeatedly.
    • table S1. The characteristics of MoS2-based TFTs with different device structures.
    • Legends for movies S1 and S2
    • Reference (36)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). Active-matrix display operation on human wrist with external circuit.
    • movie S2 (.avi format). The dynamic operation of ultrathin display during peeling-off process.

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