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.
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The data that support the findings of this study are available from the corresponding authors upon request.
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).
Herz, P. R. et al. Micromotor endoscope catheter for in vivo, ultrahigh-resolution optical coherence tomography. Opt. Lett. 29, 2261–2263 (2004).
Sone, S. et al. Mass screening for lung cancer with mobile spiral computed tomography scanner. Lancet 351, 1242–1245 (1998).
Lochner, C. M., Khan, Y., Pierre, A. & Arias, A. C. All-organic optoelectronic sensor for pulse oximetry. Nat. Commun. 5, 5745 (2014).
Kim, J. et al. Miniaturized battery-free wireless systems for wearable pulse oximetry. Adv. Funct. Mater. 27, 1604373 (2017).
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).
Yokota, T. et al. Ultraflexible organic photonic skin. Sci. Adv. 2, e1501856 (2016).
Khan, Y. et al. A flexible organic reflectance oximeter array. Proc. Natl Acad. Sci. USA 115, E11015–E11024 (2018).
Xu, H. et al. Flexible organic/inorganic hybrid near infrared photoplethysmogram sensor for cardiovascular monitoring. Adv. Mater. 29, 1700975 (2017).
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).
Akkerman, H. et al. Printed organic photodetector arrays and their use in palmprint scanners. SID Sym. Dig. Tech. Pap. 49, 494–497 (2018).
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).
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).
Li, W. et al. Efficient tandem and triple-junction polymer solar cells. J. Am. Chem. Soc. 135, 5529–5532 (2013).
Park, S. et al. Ultraflexible near-infrared organic photodetectors for conformal photoplethysmogram sensors. Adv. Mater. 30, 1802359 (2018).
Siegmund, B. et al. Organic narrowband near-infrared photodetectors based on intermolecular charge-transfer absorption. Nat. Commun. 8, 15421 (2017).
Rauch, T. et al. Near-infrared imaging with quantum-dotsensitized organic photodiodes. Nat. Photon. 3, 332–336 (2009).
Simone, G. et al. Near infrared tandem organic photodiodes for future application in artificial retinal implants solar cells. Adv. Mater. 30, 1802359 (2018).
Kaltenbrunner, M. et al. An ultra-lightweight design for imperceptible plastic electronics. Nature 499, 458–463 (2013).
Powell, M. J. The physics of amorphous-silicon thin-film transistors. IEEE Trans. Electron Devices 36, 2753–2763 (1989).
Kang, B., Lee, W. H. & Cho, K. Recent advances in organic transistor printing processes. ACS Appl. Mater. Interfaces 5, 2302–2315 (2013).
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).
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).
Hong, L. & Jain, A. Classification of fingerprint images. Proc. Scand. Conf. Image Anal. 2, 665–672 (1999).
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).
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).
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).
Yelderman, M. & New, W. Jr Evaluation of pulse oxymetry. Anesthesiology 59, 349–351 (1983).
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).
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).
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).
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).
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).
Pierre, A., Deckman, I., Lechêne, P. B. & Arias, A. C. High detectivity all-printed organic photodiodes. Adv. Mater. 27, 6411–6417 (2015).
This work was financially supported by JST ACCEL (grant no. JPMJMI17F1).
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
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
Advanced Materials Technologies (2021)
Journal of Materials Chemistry C (2021)
Advanced Materials (2021)
Advanced Functional Materials (2021)
Nature Communications (2021)