Nanowire active-matrix circuitry for low-voltage macroscale artificial skin

Journal name:
Nature Materials
Volume:
9,
Pages:
821–826
Year published:
DOI:
doi:10.1038/nmat2835
Received
Accepted
Published online

Large-scale integration of high-performance electronic components on mechanically flexible substrates may enable new applications in electronics, sensing and energy1, 2, 3, 4, 5, 6, 7, 8. Over the past several years, tremendous progress in the printing and transfer of single-crystalline, inorganic micro- and nanostructures on plastic substrates has been achieved through various process schemes5, 6, 7, 8, 9, 10. For instance, contact printing of parallel arrays of semiconductor nanowires (NWs) has been explored as a versatile route to enable fabrication of high-performance, bendable transistors and sensors11, 12, 13, 14. However, truly macroscale integration of ordered NW circuitry has not yet been demonstrated, with the largest-scale active systems being of the order of 1 cm2 (refs 11,15). This limitation is in part due to assembly- and processing-related obstacles, although larger-scale integration has been demonstrated for randomly oriented NWs (ref. 16). Driven by this challenge, here we demonstrate macroscale (7×7 cm2) integration of parallel NW arrays as the active-matrix backplane of a flexible pressure-sensor array (18×19 pixels). The integrated sensor array effectively functions as an artificial electronic skin2, 17, 18, capable of monitoring applied pressure profiles with high spatial resolution. The active-matrix circuitry operates at a low operating voltage of less than 5 V and exhibits superb mechanical robustness and reliability, without performance degradation on bending to small radii of curvature (2.5 mm) for over 2,000 bending cycles. This work presents the largest integration of ordered NW-array active components, and demonstrates a model platform for future integration of nanomaterials for practical applications.

At a glance

Figures

  1. Nanowire-based macroscale flexible devices.
    Figure 1: Nanowire-based macroscale flexible devices.

    a, Schematic of the passive and active layers of NW e-skin (see Methods). b,c, Optical photographs of a fully fabricated e-skin device (7×7 cm2 with a 19×18 pixel array) under bending (b) and rolling (c) conditions. d, Optical-microscope image of a single sensor pixel in the array, depicting a Ge/Si NW-array FET (channel length ∼3 μm, channel width ∼250 μm) integrated with a PSR. The circuit structure for the pixel is also shown. e,f, Scanning electron micrographs of a NW-array FET, showing the high degree of NW alignment and uniformity achieved by contact printing with a density of ∼5 NWs μm−1.

  2. Electrical characterization of NW-array FETs.
    Figure 2: Electrical characterization of NW-array FETs.

    a,b, Output and transfer characteristics of a representative NW FET on a polyimide substrate, before the lamination of the PSR. cIDSVGS curves as a function of an applied pressure for a representative pixel after the lamination of the PSR. In this case, the source electrode of the NW-array FET is connected to ground through the rubber. d, The pressure dependence of the pixel output conductance at VGS=VDS=−3 V. The log-scale plot is show in the inset.

  3. Time-resolved measurements of the sensor response.
    Figure 3: Time-resolved measurements of the sensor response.

    a, Schematic of the experimental set-up. A stepping motor and a force sensor controlled by a computer were used to control the applied pressure and frequency while the output signal was recorded at VDS=3 V and VGS=−5 V. b, Normalized output signal of a pixel during the relaxation step (that is, when the pressure is released), showing a response time of <0.1 s. The output signal is normalized by the maximum conductance, Gmax, of the pixel at 15 kPa. The applied pressure profile is also shown. c, Time-resolved measurements of the output signal for an applied pressure frequency of 1 Hz (left), 3 Hz (middle) and 5 Hz (right).

  4. Mechanical testing of integrated pressure-sensor devices.
    Figure 4: Mechanical testing of integrated pressure-sensor devices.

    a, The normalized conductance change, ΔG/Go, of a representative pixel at different curvature radii. The insets illustrate the device structure and bending orientation used in the experiments. b, ΔG/Go as a function of mechanical bending cycles, demonstrating the mechanical robustness of the devices with minimal performance degradation even after 2,000 cycles of bending and relaxing. c, Theoretical simulation of the strain for a NW device when bent to a 2.5 mm curvature radius. A symmetric right boundary condition is assumed in the simulation; therefore, only half of the device is shown.

  5. Fully integrated, artificial e-skin with NW active-matrix backplane.
    Figure 5: Fully integrated, artificial e-skin with NW active-matrix backplane.

    a, Photograph of a fabricated e-skin with a PDMS mould in the shape of ‘C’ placed on the top for applying pressure and subsequent imaging. b, Circuit schematic of the active matrix to address individual pixels by applying row (VBL) and column (VWL) signals. c, Design layout of the sensor device. d, The corresponding two-dimensional intensity profile obtained from experimental mapping of the pixel signals. The character ‘C’, corresponding to the applied pressure profile, can be readily imaged by the e-skin.

References

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Author information

Affiliations

  1. Department of Electrical Engineering and Computer Sciences, University of California at Berkeley, Berkeley, California 94702, USA

    • Kuniharu Takei,
    • Toshitake Takahashi,
    • Johnny C. Ho,
    • Hyunhyub Ko,
    • Paul W. Leu,
    • Ronald S. Fearing &
    • Ali Javey
  2. Berkeley Sensor and Actuator Center, University of California at Berkeley, Berkeley, California 94720, USA

    • Kuniharu Takei,
    • Toshitake Takahashi,
    • Johnny C. Ho,
    • Hyunhyub Ko,
    • Paul W. Leu &
    • Ali Javey
  3. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Kuniharu Takei,
    • Toshitake Takahashi,
    • Johnny C. Ho,
    • Hyunhyub Ko,
    • Paul W. Leu &
    • Ali Javey
  4. Department of Mechanical Engineering, University of California at Berkeley, Berkeley, California 94702, USA

    • Andrew G. Gillies
  5. Present address: School of Nano-Biotechnology & Chemical Engineering, Ulsan National Institute of Science and Technology, Ulsan Metropolitan City 689-798, South Korea

    • Hyunhyub Ko

Contributions

K.T., T.T. and A.J. designed the experiments. K.T., T.T., A.G.G., J.C.H. and H.K. carried out experiments. K.T. and P.W.L. carried out simulations. K.T., T.T., P.W.L. and A.J. contributed to analysing the data. K.T. and A.J. wrote the Letter and all authors provided feedback.

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The authors declare no competing financial interests.

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