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Open AccessArticle

Toward the Super Temporal Resolution Image Sensor with a Germanium Photodiode for Visible Light

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School of Science and Engineering, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan
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School of Electronics and Telecommunications, Hanoi University of Science and Technology, 1 Dai Co Viet, Bach Khoa, Hai Ba Trung, Hanoi 100803, Vietnam
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IMEC, 3001 Leuven, Belgium
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Faculty of Information Science and Technology, Osaka Institute of Technology, Hirakata Campus, 1-79-1 Kitayama, Hirakata City, Osaka 573-0196, Japan
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Link Research Corporation, 291-4, Kuno, Odawara-shi, Kanagawa 250-0055, Japan
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Graduate School of Engineering, Osaka University, 1-1 Yamada-oka, Suita, Osaka 565-0871, Japan
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Department of Civil and Environmental Engineering, School of Science and Engineering, Kindai University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
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Advanced Quantum Architecture Laboratory, EPFL, Rue de la Maladière 71b, Case Postale 526, CH-2002 Neuchâtel, Switzerland
*
Author to whom correspondence should be addressed.
Sensors 2020, 20(23), 6895; https://doi.org/10.3390/s20236895
Received: 30 October 2020 / Revised: 19 November 2020 / Accepted: 24 November 2020 / Published: 2 December 2020
(This article belongs to the Special Issue Advances in High-Speed CMOS Image Sensor and Related Technologies)
The theoretical temporal resolution limit tT of a silicon photodiode (Si PD) is 11.1 ps. We call “super temporal resolution” the temporal resolution that is shorter than that limit. To achieve this resolution, Germanium is selected as a candidate material for the photodiode (Ge PD) for visible light since the absorption coefficient of Ge for the wavelength is several tens of times higher than that of Si, allowing a very thin PD. On the other hand, the saturation drift velocity of electrons in Ge is about 2/3 of that in Si. The ratio suggests an ultra-short propagation time of electrons in the Ge PD. However, the diffusion coefficient of electrons in Ge is four times higher than that of Si. Therefore, Monte Carlo simulations were applied to analyze the temporal resolution of the Ge PD. The estimated theoretical temporal resolution limit is 0.26 ps, while the practical limit is 1.41 ps. To achieve a super temporal resolution better than 11.1 ps, the driver circuit must operate at least 100 GHz. It is thus proposed to develop, at first, a short-wavelength infrared (SWIR) ultra-high-speed image sensor with a thicker and wider Ge PD, and then gradually decrease the size along with the progress of the driver circuits. View Full-Text
Keywords: ultra-high-speed; super temporal resolution; temporal resolution limit; image sensor; visible light; SWIR; germanium ultra-high-speed; super temporal resolution; temporal resolution limit; image sensor; visible light; SWIR; germanium
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MDPI and ACS Style

Ngo, N.H.; Nguyen, A.Q.; Bufler, F.M.; Kamakura, Y.; Mutoh, H.; Shimura, T.; Hosoi, T.; Watanabe, H.; Matagne, P.; Shimonomura, K.; Takehara, K.; Charbon, E.; Etoh, T.G. Toward the Super Temporal Resolution Image Sensor with a Germanium Photodiode for Visible Light. Sensors 2020, 20, 6895.

AMA Style

Ngo NH, Nguyen AQ, Bufler FM, Kamakura Y, Mutoh H, Shimura T, Hosoi T, Watanabe H, Matagne P, Shimonomura K, Takehara K, Charbon E, Etoh TG. Toward the Super Temporal Resolution Image Sensor with a Germanium Photodiode for Visible Light. Sensors. 2020; 20(23):6895.

Chicago/Turabian Style

Ngo, Nguyen H.; Nguyen, Anh Q.; Bufler, Fabian M.; Kamakura, Yoshinari; Mutoh, Hideki; Shimura, Takayoshi; Hosoi, Takuji; Watanabe, Heiji; Matagne, Philippe; Shimonomura, Kazuhiro; Takehara, Kohsei; Charbon, Edoardo; Etoh, Takeharu G. 2020. "Toward the Super Temporal Resolution Image Sensor with a Germanium Photodiode for Visible Light" Sensors 20, no. 23: 6895.

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