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SCIENCE CHINA Information Sciences, Volume 62, Issue 10: 202403(2019) https://doi.org/10.1007/s11432-019-9918-4

Printed flexible thin-film transistors based on different types of modified liquid metal with good mobility

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  • ReceivedMar 6, 2019
  • AcceptedJun 12, 2019
  • PublishedAug 29, 2019

Abstract

High-performance logic circuits fabricated on flexible or unconventional substrates have become a necessity for several new applications. Generally, compared to those fabricated on more rigid substrates, printed, large-area, and flexible thin film transistors (TFTs) are prone to under-performance, which severely limits their practical value. The realization of printed flexible macroelectronics requires advancements in material science and novel fabricating techniques. In this study, using a fast printing process, we manufacture liquid metal-carbon nanotube TFTs on a thin polyethylene terephthalate substrate. These flexible TFTs (p-type) exhibit enhance stability and flexibility, carrier mobility (10.61 ${\rm~cm}^2{\rm~V}^{-1}{\rm~s}^{-1}$), and transconductance (0.88 $\mu$S). Furthermore, we realize dependable n-type and ambipolar transistors based on liquid metals with charge transport efficiencies that are comparable to our p-type counterparts, thus providing a foundation for manufacturing integrated circuits and complementary logic gates on flexible substrates. This study shows the positive progress of liquid metal printing-enabled functional devices and discusses the possibility of practical applications; moreover, it sets the foundation for printed high-performance and large-area flexible liquid metal electronics.


Acknowledgment

This work was partially supported by National Natural Science Foundation of China Key Project (Grant No. 91748206), Dean's Research Funding and the Frontier Project of the Chinese Academy of Sciences. Qian LI acknowledges the support by China Postdoctoral Science Foundation (Grant No. 2018M641485). The authors are grateful for the support of Beijing DREAM Ink Technologies Co., Ltd.


Supplement

Figures S1–S8, Tables S1 and S2.


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  • Figure 1

    (Color online) Flexible liquid metal conductors fabricated by the doping method. (a) SEM images of a liquid metal EGaIn droplet and LM-1: GaSn-Ag@Cu, LM-2: GaIn-Ag@Cu-1, LM-3: GaIn-Ag@Cu-2, LM-4: GaIn-Ag@Cu-3, LM-5: GaIn-Ni-CNTs, LM-6: GaIn-Ni, and LM-7: GaIn-CNTs. Scale bar, 50 $\mu$m. The doping concentration of the different doping elements results in different morphologies. (b) EDS mapping of LM-1. The overlapped mappings of the GaSn-Ag@Cu liquid metal clearly show the distribution of gallium, tin, and copper, and the presence of nanomaterials covering the surface. (c) EDS spectra of the GaSn-Ag@Cu (LM-1), GaIn-Ag@Cu-1 (LM-2), and GaIn-Ag@Cu-2 (LM-3) electrodes by printing. (d) A comparison of this work to recent work on elastic conductors, including Ag nanowires (Ag NW), Au nanoparticles (Au NP), Ag nanoparticles (Ag NP), multi-walled carbon nanotubes (MWCNT), single-walled carbon nanotubes (SWCNT), polyaniline (PANI), and this study (corresponds to red star). Our liquid metals show the best conductivity and stretchability. Inset: plot showing the conductivity of the seven metals.

  • Figure 2

    (Color online) Printed liquid metal CNT transistors on flexible films. (a) Schematic of a flexible LM/CTFT device. (b) and (c) Image of an array of LM/CTFTs on a thin PET. The devices are fabricated with printing processes. (d) A metallographic microscope image of the channel region. Scale bar, 50 $\mu$m.

  • Figure 3

    (Color online) Performance under ambient conditions of representative liquid metal CNT transistors with a CNT semiconductor and various liquid metal electrodes. The TFT transfer plot of the current versus $V_{\rm~GS}$ for (a) LM-1/CNT, (b) LM-2/CNT, and (c) LM-3/CNT devices at $V_{\rm~DS}=|5|$ V. The channel length and width of all devices are 50 $\mu$m and 2000 $\mu$m, respectively. (d) TLM plot of the total resistance ($R_{\rm~total}$) as a function of channel length ($L_{\rm~ch}$) for each type of metal/CNT contact configuration. (e) Plot of the mobilities versus transconductance to compare the representative flexible TFTs reported in the literature. Our TFTs exhibit the highest mobilities.

  • Figure 4

    (Color online) LM/CTFT stability data under ambient conditions. (a) and (b) LM/CTFTs performance, including field-effect mobility and on/off current ratio as a function of the bending cycles. All metrics exhibit negligible variations after 1000 cycles, indicating the excellent flexibility of the devices. (c) and (d) Transistor performance parameters versus time plots for the LM/CTFTs. All metrics exhibit negligible variations after 50 d, indicating the excellent reliability of the devices. The channel length and width for all devices are 50 and 2000 $\mu$m, respectively.

  • Table 1   Different doping elements and mass ratio of seven kinds of liquid metal$^{\rm~a)}$
    Liquid metal Raw materials Mass ratio Mass ratio of elements
    crlr)4-10GaInSnCuNiCOcrGaSn-Ag@CuGaSn, $H_1$(Ag@Cu)100:1574.94%10.20%6.56%7.27%1.03%crGaIn-Ag@Cu-1EGaIn, $H_{20}$(Ag@Cu)100:1566.21%27.50%2.33%3.95%–crGaIn-Ag@Cu-2EGaIn, $H_1$(Ag@Cu)100:1067.86%23.41%2.88%5.85%–crGaIn-Ag@Cu-3EGaIn, $C_1$(Ag@Cu)100:1568.19%22.68%2.13%6.12%0.88%crGaIn-Ni-CNTsEGaIn, Ni, CWNT100:2:1.570.94%21.78%1.05%6.22%–crGaIn-NiEGaIn, Ni100:469.08%23.58%1.12%6.22%–crGaIn-CNTEGaIn, CNT100:272.30%21.21%6.49%–cr

    a

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