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Active pixel sensor matrix based on monolayer MoS2 phototransistor array

Abstract

In-sensor processing, which can reduce the energy and hardware burden for many machine vision applications, is currently lacking in state-of-the-art active pixel sensor (APS) technology. Photosensitive and semiconducting two-dimensional (2D) materials can bridge this technology gap by integrating image capture (sense) and image processing (compute) capabilities in a single device. Here, we introduce a 2D APS technology based on a monolayer MoS2 phototransistor array, where each pixel uses a single programmable phototransistor, leading to a substantial reduction in footprint (900 pixels in 0.09 cm2) and energy consumption (100s of fJ per pixel). By exploiting gate-tunable persistent photoconductivity, we achieve a responsivity of 3.6 × 107 A W−1, specific detectivity of 5.6 × 1013 Jones, spectral uniformity, a high dynamic range of 80 dB and in-sensor de-noising capabilities. Further, we demonstrate near-ideal yield and uniformity in photoresponse across the 2D APS array.

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Fig. 1: 2D APS.
Fig. 2: Characterization of monolayer MoS2.
Fig. 3: Device-to-device variation in the characteristics of MoS2 phototransistors.
Fig. 4: HDR and spectral uniformity.
Fig. 5: Photodetection metrics.
Fig. 6: Fast reset and de-noising.

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Data Availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Code Availability

The codes used for plotting the data are available from the corresponding authors on reasonable request.

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Acknowledgements

The work of A.D., D.J., A.P., S.S.R. and S.D. was supported by Army Research Office (ARO) through contract number W911NF1920338 and the National Science Foundation (NSF) through CAREER Award under grant number ECCS-2042154. The work of N.T. and J.M.R. was supported by the NSF through the Pennsylvania State University 2D Crystal Consortium–Materials Innovation Platform (2DCCMIP) under NSF cooperative agreement DMR-1539916. The work of M.A.S., C.W.O. and K.L.K. was supported by the Air Force Office of Scientific Research grant number FA-9550-18-1-0347. The work of S.B. is supported by NSF CAREER DMR-1654107. The work of S.P.S. and D.E.W. was supported by the Department of Defense, Defense Threat Reduction Agency (DTRA) as part of the Interaction Ionizing Radiation with Matter University Research Alliance (IIRM-URA) under contract number HDTRA1-20-2-0002. The content of the information does not necessarily reflect the position or the policy of the federal government, and no official endorsement should be inferred.

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Authors

Contributions

S.D., A.D. and D.J. conceived the idea and designed the experiments. A.D., D.J., A.P., S.S.R. and S.D. performed the experiments, analysed the data, discussed the results and agreed on their implications. N.T. grew MOCVD MoS2 under the supervision of J.M.R. S.B. helped in the TEM sample preparation. S.P.S. performed the TEM characterization under the supervision of D.E.W. M.A.S. and C.W.O. performed the SHG measurements and simulations under the supervision of K.L.K. J.R.S. helped with the XPS measurements and analysis. All authors contributed to the preparation of the manuscript.

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Correspondence to Saptarshi Das.

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Nature Materials thanks Sunkook Kim, Dmitry Polyushkin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Raman spectroscopy of monolayer MoS2.

a, Raman spectra, and b, corresponding spatial colormap of peak separation between the two Raman active modes, \(E_{2{{{\mathrm{g}}}}}^1\) and A1g, c, PL spectra, and d, corresponding spatial colormap of PL peak position measured over a 40 µm × 40 µm area for post-transfer MoS2 film. The mean Raman peak separation was found to be ~20 cm−1 with a standard deviation of ~0.72 cm−1 and the mean PL peak position was found to be at ~1.83 eV with a standard deviation of ~0.005 eV for the post-transfer film, respectively. Bar plots for e, the mean peak separation between \(E_{2{{{\mathrm{g}}}}}^1\) and A1g Raman modes and f, mean PL peak position along with their corresponding standard deviation values for as-grown and post-transfer films obtained over 40 µm × 40 µm areas for 5 different locations.

Extended Data Fig. 2 Atomic force microscopy (AFM) of monolayer MoS2.

AFM images were taken at 4 different locations for a, as-grown and b, post-transfer MoS2 films. Although the thickness of both films was ~1 nm, we do observe polymer residues concentrating near the edges of bilayer islands and/or grain boundaries in the transferred film. This is typical of polymer-assisted transfer processes.

Extended Data Fig. 3 Hysteresis in the transfer characteristics of 2D APS.

Hysteresis in the transfer characteristics of 49 2D APS.

Extended Data Fig. 4 Post-illumination transfer characteristics of the 2D APS when exposed to different illumination intensities (Pin) for different duration (τexp).

Post-illumination transfer characteristics of the 2D APS when exposed to different Pin for different τexp periods for a, red, b, green, and c, blue illuminations, respectively. All illuminations were done at Vexp = −2 V.

Extended Data Fig. 5 Post-illumination transfer characteristics of the 2D APS when exposed to different illumination intensities (Pin) at different gate bias (Vexp).

Post-illumination transfer characteristics of the 2D APS when exposed to different Pin for different Vexp values for a, red, b, green, and c, blue illuminations, respectively. All illuminations were done for τexp = 100 ms.

Extended Data Fig. 6 Pre- and post-illumination transfer characteristics of a MoS2 phototransistor.

Pre- and post-illumination transfer characteristics of a representative MoS2 phototransistor after being exposed to blue illumination with Pin = 15 Wm−2 at Vexp = −4 V for τexp = 100 ns. Clearly, we observe a change in the post-illumination transfer characteristics, indicating that the charge trapping in the MoS2 phototransistor can occur as fast as 100 ns.

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Dodda, A., Jayachandran, D., Pannone, A. et al. Active pixel sensor matrix based on monolayer MoS2 phototransistor array. Nat. Mater. 21, 1379–1387 (2022). https://doi.org/10.1038/s41563-022-01398-9

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