Random Telegraph Noises in CMOS Image Sensors Caused by Variable Gate-Induced Sense Node Leakage Due to X-Ray Irradiation

Abstract

The effects of X-ray irradiation on the random noises, especially the random telegraph noises (RTN), of a 45-nm on 65-nm stacked CMOS image sensor with 8.3M 1.1 μm pixels are investigated. It is found that before X-ray irradiation the dominant type of RTN among the noisiest pixels is the source follower (SF) MOSFET channel RTN. In contrast, after X-ray irradiation up to a total ionizing dose of 1 Mrad(SiO 2 ), the RTN becomes dominated by the variable transfer-gate-induced sense node (SN) leakage. These two different types of RTN can be distinguished by their dependence on the transfer gate (TG) OFF voltage and the time between the correlated double sampling (CDS). The magnitude of the RTN from the variable SN leakage is proportional to the CDS time and can be suppressed effectively by increasing the TG OFF voltage, whereas the SF RTN is independent of the CDS time or the TG OFF voltage.INDEX TERMS Random noise (RN), random telegraph noise (RTN), random telegraph signal (RTS), CMOS image sensor (CIS), pinned photodiode (PPD), active pixel sensor (APS), correlated double sampling (CDS), gate induced drain leakage (GIDL), variable junction leakage (VJL), variable retention time (VRT), radiation damage, X-ray, total ionizing dose (TID).

Radiation-Induced Leakage Current and Electric Field Enhancement in CMOS Image Sensor Sense Node Floating Diffusions

“…11. These results suggest that RTS defects located under the TG oxide do not play a major role in terms of leakage current RTS before irradiation but must be considered after ionizing dose deposition as highlighted by the results shown in [29].…”

Random Telegraph Noises from the Source Follower, the Photodiode Dark Current, and the Gate-Induced Sense Node Leakage in CMOS Image Sensors

“…Instead, X-ray irradiation is utilized as a tool to alter the composition of RTN types and to increase the number of RTN pixels for investigation. As reported in [20][21][22][23], the number of RTN pixels in an 8.3 MP CIS before X-ray irradiation is in the order of 1 percent. This RTN percentage can be increased significantly by X-ray irradiation.…”

“…The half-line even-and odd-column pixels are read out alternatively and reconstructed into a full line by an off-chip FPGA, which also generates the rolling shutter and other control signals. This chip achieves a low input-referred readout noise around 1.3 e-rms under an 8X gain [20][21][22][23].…”

“…The pixels with high RNs (blinking or twinkling pixels [7][8][9]) will create fixed-pattern temporal noises flickering from frame to frame. It is known that most of the pixels on the long distribution tails show the behavior of the random telegraph signals (RTS) [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Such noises are called the RTS noises, or the random telegraph noises (RTN).…”

“…A general study of the RTS phenomena in semiconductor devices can be found in a recent book [24], covering a wide range of experimental and theoretical topics. For CIS, the most reported RTN originate from the source followers (SF) of the active pixels [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Although other sources, such as DC-RTS, have been reported [25,26], a comprehensive discrimination and comparison of the various sources of RTN in a CIS cannot be found in the literature yet.…”