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A conformable imager for biometric authentication and vital sign measurement

Abstract

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.

References

  1. 1.

    Bailey, B., Farkas, D. L., Taylor, D. L. & Lanni, F. Enhancement of axial resolution in fluorescence microscopy by standing-wave excitation. Nature 366, 44–48 (1993).

    Article  Google Scholar 

  2. 2.

    Herz, P. R. et al. Micromotor endoscope catheter for in vivo, ultrahigh-resolution optical coherence tomography. Opt. Lett. 29, 2261–2263 (2004).

    Article  Google Scholar 

  3. 3.

    Sone, S. et al. Mass screening for lung cancer with mobile spiral computed tomography scanner. Lancet 351, 1242–1245 (1998).

    Article  Google Scholar 

  4. 4.

    Lochner, C. M., Khan, Y., Pierre, A. & Arias, A. C. All-organic optoelectronic sensor for pulse oximetry. Nat. Commun. 5, 5745 (2014).

    Article  Google Scholar 

  5. 5.

    Kim, J. et al. Miniaturized battery-free wireless systems for wearable pulse oximetry. Adv. Funct. Mater. 27, 1604373 (2017).

    Article  Google Scholar 

  6. 6.

    Wu, Z., Yao, W., London, A. E., Azoulay, J. D. & Ng, T. N. Temperature-dependent detectivity of near-infrared organic bulk heterojunction photodiodes. ACS Appl. Mater. Interfaces 9, 1654–1660 (2017).

    Article  Google Scholar 

  7. 7.

    Yokota, T. et al. Ultraflexible organic photonic skin. Sci. Adv. 2, e1501856 (2016).

    Article  Google Scholar 

  8. 8.

    Khan, Y. et al. A flexible organic reflectance oximeter array. Proc. Natl Acad. Sci. USA 115, E11015–E11024 (2018).

    Article  Google Scholar 

  9. 9.

    Xu, H. et al. Flexible organic/inorganic hybrid near infrared photoplethysmogram sensor for cardiovascular monitoring. Adv. Mater. 29, 1700975 (2017).

    Article  Google Scholar 

  10. 10.

    Qin, Y., Wang, H. & Liu, Y. Organic–inorganic hybrid thin-film photo-detector for fingerprint recognition. SID Sym. Dig. Tech. Pap. 49, 1604–1606 (2018).

    Article  Google Scholar 

  11. 11.

    Akkerman, H. et al. Printed organic photodetector arrays and their use in palmprint scanners. SID Sym. Dig. Tech. Pap. 49, 494–497 (2018).

    Article  Google Scholar 

  12. 12.

    Banach, M., Markham, S., Agaiby, R. & Too, P. Low leakage organic backplanes for high pixel density optical sensors. SID Sym. Dig. Tech. Pap. 49, 90–91 (2018).

    Article  Google Scholar 

  13. 13.

    Persidis, E., Baur, H., Pieralisi, F., Schalbergfer, P. & Fruehauf, N. Area laser crystallized LTPS TFTs with implanted contacts for active matrix OLED displays. Solid State Electron. 52, 455–461 (2008).

    Article  Google Scholar 

  14. 14.

    Li, W. et al. Efficient tandem and triple-junction polymer solar cells. J. Am. Chem. Soc. 135, 5529–5532 (2013).

    Article  Google Scholar 

  15. 15.

    Park, S. et al. Ultraflexible near-infrared organic photodetectors for conformal photoplethysmogram sensors. Adv. Mater. 30, 1802359 (2018).

    Article  Google Scholar 

  16. 16.

    Siegmund, B. et al. Organic narrowband near-infrared photodetectors based on intermolecular charge-transfer absorption. Nat. Commun. 8, 15421 (2017).

    Article  Google Scholar 

  17. 17.

    Rauch, T. et al. Near-infrared imaging with quantum-dotsensitized organic photodiodes. Nat. Photon. 3, 332–336 (2009).

    Article  Google Scholar 

  18. 18.

    Simone, G. et al. Near infrared tandem organic photodiodes for future application in artificial retinal implants solar cells. Adv. Mater. 30, 1802359 (2018).

    Article  Google Scholar 

  19. 19.

    Kaltenbrunner, M. et al. An ultra-lightweight design for imperceptible plastic electronics. Nature 499, 458–463 (2013).

    Article  Google Scholar 

  20. 20.

    Powell, M. J. The physics of amorphous-silicon thin-film transistors. IEEE Trans. Electron Devices 36, 2753–2763 (1989).

    Article  Google Scholar 

  21. 21.

    Kang, B., Lee, W. H. & Cho, K. Recent advances in organic transistor printing processes. ACS Appl. Mater. Interfaces 5, 2302–2315 (2013).

    Article  Google Scholar 

  22. 22.

    Nathan, A. et al. Amorphous silicon thin film transistor circuitintegration for organic LED displays on glass and plastic. IEEE J. Solid-State Circuits 39, 1477–1486 (2004).

    Article  Google Scholar 

  23. 23.

    Jain, A., Chen, Y. & Demirkus, M. Pores and ridges: high-resolution fingerprint matching using level 3 features. IEEE Trans. Pattern Anal. Mach. Intell. 29, 15–27 (2007).

    Article  Google Scholar 

  24. 24.

    Hong, L. & Jain, A. Classification of fingerprint images. Proc. Scand. Conf. Image Anal. 2, 665–672 (1999).

    Google Scholar 

  25. 25.

    Kang, B. J., Park, K. R., Yoo, J. H. & Kim, J. N. Multimodal biometric method that combines veins, prints and shape of a finger. Opt. Eng. 50, 017201 (2011).

    Article  Google Scholar 

  26. 26.

    Ratha, N. K., Connell, J. H. & Bolle, R. M. Enhancing security and privacy in biometrics-based authentication systems. IBM Syst. J. 40, 614–634 (2001).

    Article  Google Scholar 

  27. 27.

    Kachuee, M., Kiani, M. M., Mohammadzade, H. & Shabany, M. Cuff-less high-accuracy calibration-free blood pressure estimation using pulse transit time. In Proceedings of IEEE International Symposium on Circuits and Systems 1006–1009 (IEEE, 2015).

  28. 28.

    Yelderman, M. & New, W. Jr Evaluation of pulse oxymetry. Anesthesiology 59, 349–351 (1983).

    Article  Google Scholar 

  29. 29.

    Stratton, J. R., Lighty, G. W. Jr, Pearlman, A. S. & Ritchie, J. L. Detection of left ventricular thrombus by two-dimensional echocardiography: sensitivity, specificity and causes of uncertainty. Circulation 66, 156–166 (1982).

    Article  Google Scholar 

  30. 30.

    Tamaki, T., Sawada, K., Hayashi, S., Node, Y. & Teramoto, A. Carotid atherosclerosis and arterial peripheral pulse wave velocity in cerebral thrombosis. J. Clin. Neurosci. 13, 45–49 (2006).

    Article  Google Scholar 

  31. 31.

    Nakano, T., Ohkuma, H. & Suzuki, S. Assessment of vascular injury in patients with stroke by measurement of pulse wave velocity. J. Stroke Cerebrovasc. Dis. 13, 74–80 (2004).

    Article  Google Scholar 

  32. 32.

    Nishimura, M., Takebayashi, K., Hishinuma, M., Yamaguchi, H. & Murayama, A. 5.5-inch full HD foldable AMOLED display based on neutral-plane splitting concept. SID Symp. Dig. Tech. Pap. 50, 636–639 (2019).

    Article  Google Scholar 

  33. 33.

    Schylz, M., Mack, M., Kolloge, O., Lutzen, A. & Schiek, M. Organic photodiodes from homochiral l-proline derived squaraine compounds with strong circular dichroism. Phys. Chem. Chem. Phys. 19, 6996–7008 (2017).

    Article  Google Scholar 

  34. 34.

    Pierre, A., Deckman, I., Lechêne, P. B. & Arias, A. C. High detectivity all-printed organic photodiodes. Adv. Mater. 27, 6411–6417 (2015).

    Article  Google Scholar 

Download references

Acknowledgements

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

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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). https://doi.org/10.1038/s41928-019-0354-7

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