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Flexible metal-oxide devices made by room-temperature photochemical activation of sol–gel films


Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors1,2,3,4,5,6,7. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates8,9,10,11,12,13. But metal-oxide formation by the sol–gel route requires an annealing step at relatively high temperature2,14,15,16,17,18,19, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol–gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7 cm2 V−1 s−1 (with an Al2O3 gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340 kHz, corresponding to a propagation delay of less than 210 nanoseconds per stage.

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Figure 1: Photo-activation of solution-processed metal-oxide semiconductors by DUV.
Figure 2: Transfer characteristics of photo-annealed IGZO, IZO and In 2 O 3 TFTs using Al 2 O 3 and SiO 2 gate dielectric, and comparison with thermally annealed devices.
Figure 3: Electrical characteristics and bias stability of photo-annealed IGZO TFTs on flexible substrates.
Figure 4: Characteristics of seven-stage ring oscillators fabricated on a PAR substrate by photo-annealing.


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We acknowledge discussions with C.-I. Kim, S.-H. Song, H.-I. Kwon, B.-S. Bae, Y. Hong, S. Lim, J.-I. Han, M. J. Lee, A. Fenoglio and K.-H. Kim. This work was partially supported by Basic Science Research Program (no. 2010-0002623) and World-Class University Program (no. R31-10026) through a National Research Foundation of Korea (NRF) grant funded by the Ministry of Education, Science, and Technology.

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S.K.P. designed the project and experiments; Y.-H.K., J.-S.H., T.-H.K., S.P., J.K., M.S.O., M.-H.Y. and S.K.P. carried out the experiments; S.K.P. and Y.-H.K. discussed and interpreted all the results; M.-H.Y., G.-R.Y. and Y.-Y.N. gave conceptual advice on the chemistry-related experiments and discussions. S.K.P., Y.-H.K., M.-H.Y. and G.-R.Y. wrote the manuscript, with S.K.P. the lead writer. All authors read and commented on the manuscript.

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Correspondence to Sung Kyu Park.

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The authors declare no competing financial interests.

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Kim, YH., Heo, JS., Kim, TH. et al. Flexible metal-oxide devices made by room-temperature photochemical activation of sol–gel films. Nature 489, 128–132 (2012).

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