6 Types of Random Telegraph Noise

Image Sensors World        Go to the original article...

TSMC, French Atomique Energie Commission, and Institut supérieur de l’aéronautique et de l’espace, Toulouse, publish a joint MDPI paper "Random Telegraph Noises from the Source Follower, the Photodiode Dark Current, and the Gate-Induced Sense Node Leakage in CMOS Image Sensors" by Calvin Yi-Ping Chao, Shang-Fu Yeh, Meng-Hsu Wu, Kuo-Yu Chou, Honyih Tu, Chih-Lin Lee, Chin Yin, Philippe Paillet, and Vincent Goiffon. The paper is a part of MDPI Special issue on the 2019 International Image Sensor Workshop (IISW2019).

"In this paper we present a systematic approach to sort out different types of random telegraph noises (RTN) in CMOS image sensors (CIS) by examining their dependencies on the transfer gate off-voltage, the reset gate off-voltage, the photodiode integration time, and the sense node charge retention time. Besides the well-known source follower RTN, we have identified the RTN caused by varying photodiode dark current, transfer-gate and reset-gate induced sense node leakage. These four types of RTN and the dark signal shot noises dominate the noise distribution tails of CIS and non-CIS chips under test, either with or without X-ray irradiation. The effect of correlated multiple sampling (CMS) on noise reduction is studied and a theoretical model is developed to account for the measurement results."


"Continued improvement of RTN is essential for enhancing CIS performance when the pixel scales down to 0.7 um pitch and beyond. Understanding the RTN behavior and classification of the RTN pixels into different types are the necessary first step in order to reduce RTN through pixel design and minimizing process-induced damage (PID). In this paper, we identified the SF-RTN, the DC-RTN, the TG GIDL-RTN, and the RST GIDL-RTN in active pixels according to their dependence on the PD integration time, the SN charge retention time, the 𝑉𝐷𝐺 across the TG device, and the 𝑉𝑆𝐺 across the RST device, in CIS and non-CIS chips, with and without X-ray irradiation.

We further studied the effect of CMS as a useful technique for RTN reduction through circuit design. A theoretical model was presented to account for the time-dependence of the effectiveness of CMS, which explained the measured data reasonably well. The process nodes used to manufacture the pixel-array and the ASIC layers in stacked CIS are expected to move down the path of the Moore’s Law gradually. Extending the study of RTN to highK metal gate and FinFET technologies is an important goal for our future investigation.
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