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An ultraflexible organic differential amplifier for recording electrocardiograms

Abstract

Differential amplifiers based on organic thin-film transistors (OTFTs) are attractive for monitoring human vital signs because of their signal amplification and noise elimination capabilities. However, substantial variations in OTFTs lead to the degradation of signal processing performance in circuits and restrict the development of organic differential amplifiers capable of recording weak physiological potentials. Here, we report a 2-μm-thick ultraflexible organic differential amplifier capable of processing physiological signals with high signal integrity and sensitivity. Our approach uses a circuit design and compensation technique that suppress the mismatch among OTFTs to less than a few percent. This leads to a common-mode noise attenuation factor below −12 dB, even during bending to ~50 μm. Using our flexible amplifier, we monitor electrocardiogram signals, where the power of 60 Hz electrical harmonic noise was reduced ~60 times during amplification, yielding electrocardiogram signals with a signal-to-noise ratio of 34 dB.

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Fig. 1: Ultraflexible signal-processing circuit with functionality on foil.
Fig. 2: Circuit strategy for a differential amplifier with p-type OTFTs.
Fig. 3: Organic differential amplifier on ultraflexible foil.
Fig. 4: PMC process for the organic differential amplifier.
Fig. 5: Electrical performance of the organic differential amplifier.
Fig. 6: ECG monitoring using an ultraflexible processing circuit on foil.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI grant (nos. JP16H01857, JP18H01861 and JP19J22073), the New Energy and Industrial Technology Development Organization (NEDO), the Center of Innovation Program from Japan Science and Technology Agency (JST), grant from the Commissioned Research of NICT and the Brain Mapping by Integrated Neurotechnologies for Disease Studies (Brain/MINDS) project of the Japan Agency for Medical Research and Development (AMED). Part of this work was performed at the Advanced Photonics and Biosensing Open Innovation Laboratory, National Institute of Advanced Industrial Science and Technology (AIST). This work for circuit simulation and design was supported by VLSI Design and Education Center (VDEC), the University of Tokyo, in collaboration with Synopsys and Cadence Design Systems. The authors thank Nippon Kayaku Co. for supplying DNTT and Daisan Kasei Co. for high-purity parylene (diX-SR).

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Authors

Contributions

M.S., T.U. and T.S. conceived the concept and experiments. M.S., M.A. and S.Y. designed the circuit and conceived the process for mismatch compensation. M.S., T.U., M.K. and N.N. developed the fabrication process for OTFTs and fabricated the device. M.S. carried out all experiments for device characterization and data collection for the organic circuit, with help from T.U., M.K., M.A. and N.N. M.S. wrote the manuscript in consultation with T.U., S.Y., Y.N., T.A. and T.S. All authors commented on the manuscript.

Corresponding author

Correspondence to Tsuyoshi Sekitani.

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The authors declare no competing interests.

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Supplementary Information

Supplementary Figs. 1–15 and Supplementary Tables 1–2.

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Sugiyama, M., Uemura, T., Kondo, M. et al. An ultraflexible organic differential amplifier for recording electrocardiograms. Nat Electron 2, 351–360 (2019). https://doi.org/10.1038/s41928-019-0283-5

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