Slimmer, Non-Destructive Image Sensor Unveiled

　While photo-thermoelectric (PTE) sensors are potentially suitable for testing applications, such as non-destructive material-identification in ultrabroad millimeter-wave (MMW)–infrared (IR) bands, their device designs have primarily employed a single material as the channel. In general, PTE sensors combine photo-induced heating with associated thermoelectric (TE) conversion, and the employment of a single material channel regulates the utilization of devices by missing the opportunity for fully utilizing their fundamental parameters. Here, long-standing technical difficulties in the PTE sensor design field induce such crucial situations, where typical constituent materials exhibit trade-off trends between photo-absorptance values (for heating) and the Seebeck coefficients (for TE conversion).

　To this end, this manuscript made the following significant contributions.

1. Developing the PTE sensor structure in an effective hybrid combination between bismuth composite (Bi_com) TE electrodes (Seebeck coefficient > 100 µV/K) and highly efficient carbon nanotube (CNT) film photo-thermal absorber channels.
2. Performing photo-detection operations by the sensor with over ten-fold response intensities than those of single-material PTE detectors (typically: pn-junction CNT films) as making the most of the above advantageous hybrid strategy, satisfying the readable signal range criteria (> several millivolts) for the device coupling with portable circuit modules.
3. Designing the hybrid PTE sensor into all-solution-processable fabrication configurations by effectively arranging Bi_com powders with conductive solvents and surfactants as paste-like stable TE converting electrodes, along the inherently ink-formed CNT film absorber.
4. Achieving ultrabroad MMW–IR operations with the hybrid paste PTE device over typical wideband detectors in comparable sensitivities (minimum noise equivalent power: 560 fWHz^−1/2) to existing narrowband sensors, while simultaneously maintaining optical stabilities against severe environmental conditions (e.g., high-temperatures and cyclic deformations).
5. Demonstrating functional non-destructive imaging inspections at high-usability with the hybrid PTE sensor based on the advantages above optical features and paste-unique freely paintable device setups, such as omni-directional observations of a 3D target without blin-spot by fabricating an easy-to-handle panoramic bowl camera module.

　The paper was published online in the international scientific journal, Small Science (February 20, 2025).

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Kou Li: Assistant Professor, Department of Electrical, Electronic, and Communication Engineering, Faculty of Science and Engineering, Chuo University

Yuto Matsuzaki: Master course student, Department of Electrical, Electronic, and Communication Engineering, Graduate School of Science and Engineering, Chuo University

Yukio Kawano: Department of Electrical, Professor, Electronic, and Communication Engineering, Faculty of Science and Engineering, Chuo University

Reiji Tadenuma: Bachelor student (at the time of research), Department of Electrical, Electronic, and Communication Engineering, Faculty of Science and Engineering, Chuo University

Yuto Aoshima: Bachelor student (at the time of research), Department of Electrical, Electronic, and Communication Engineering, Faculty of Science and Engineering, Chuo University

Yuto Matsuzaki^†,1, Reiji Tadenuma^†,1, Yuto Aoshima^†,1, Minami Yamamoto¹, Leo Takai¹, Yukito Kon¹, Daiki Sakai¹, Norika Takahashi¹, Ryo Koshimizu¹, Qi Zhang¹, Naoko Hagiwara¹, Meiling Sun^2,3, Daiki Shikichi¹, Raito Ota¹, Sayaka Hirokawa¹, Yukio Kawano*^1,4,5, and Kou Li*^,1

†Co-first author

^*Corresponding author

K.L., Y.M., and Y.Ka. conceptualized this work and coordinated the experiments. Y.M. and K.L. wrote the manuscript. Y.M., R.T., Y.A., M.Y., L.T., Y.Ko., D.Sa., N.T., R.K., Q.Z., N.H., M.S., D.Sh., R.O., S.H., and K.L. performed the experiments.

¹Department of Electrical, Electronic, and Communication Engineering, Faculty of Science and Engineering, Chuo University

²Laboratory for Future Interdisciplinary Research of Science and Technology, Tokyo Institute of Technology

³Department of Electrical and Electronic Engineering, School of Engineering, Tokyo Institute of Technology

⁴National Institute of Informatics

⁵Kanagawa Industrial Institute of Science and Technology