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A conformable imager for biometric authentication and vital sign measurement


Flexible imagers can be placed in direct contact with a person’s skin, allowing vital signs to be monitored continuously. However, developing flexible imagers that offer both high definition and high speed has proved challenging. Here we show that a combination of polycrystalline silicon thin-film transistor readout circuits and organic photodiodes with high sensitivity in the near-infrared region can be used to create a conformable imager with a resolution of 508 pixels per inch, a speed of 41 frames per second and a total thickness of only 15 μm. The imager can read out a photocurrent of less than 10 pA with low noise, and can obtain static biometric signals, including images of fingerprints and veins, via soft contact with the skin. It can also be used to map a pulse wave, electronically selecting the best measurement location by analysing the area distribution.

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Fig. 1: Conformable imager comprising LTPS TFTs and the NIR organic photodiode.
Fig. 2: Properties of the conformable imager.
Fig. 3: Biometric imaging.
Fig. 4: Analysis of the PPG signal.

Data availability

The data that support the findings of this study are available from the corresponding authors upon request.


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This work was financially supported by JST ACCEL (grant no. JPMJMI17F1).

Author information




T.Y., T.N., M.M., M.T., M.U., M.K. and W.Y. fabricated the devices. T.Y., T.N., H.K., M.K., S.L., A.T. and T.S. performed measurements and analysed the experimental data. T.Y. and T.S. wrote the manuscript. All authors reviewed and commented on the manuscript. T.S. supervised the project.

Corresponding authors

Correspondence to Tomoyuki Yokota or Takao Someya.

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The authors declare no competing interests.

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Supplementary Figs. 1–28.

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Yokota, T., Nakamura, T., Kato, H. et al. A conformable imager for biometric authentication and vital sign measurement. Nat Electron 3, 113–121 (2020).

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