Effect of drain current on appearance probability and amplitude of random telegraph noise in low-noise CMOS image sensors

Abstract

Random telegraph noise (RTN), which occurs in in-pixel source follower (SF) transistors, has become one of the most critical problems in highsensitivity CMOS image sensors (CIS) because it is a limiting factor of dark random noise. In this paper, the behaviors of RTN toward changes in SF drain current conditions were analyzed using a low-noise array test circuit measurement system with a floor noise of 35 µV rms . In addition to statistical analysis by measuring a large number of transistors (18048 transistors), we also analyzed the behaviors of RTN parameters such as amplitude and time constants in the individual transistors. It is demonstrated that the appearance probability of RTN becomes small under a small drain current condition, although large-amplitude RTN tends to appear in a very small number of cells.

Evaluation of Low-Frequency Noise in MOSFETs Used as a Key Component in Semiconductor Memory Devices

“…I DS varied from 0.1 to 20 µA. The floor noise in this experiment was smaller than the others and was approximately 35 µV RMS [60]. In Figure 7, V RMS decreases with an increase in I DS for all V RMS .…”

“…However, the higher appearance probability in large I DS than that in small I DS for the small V RMS region of less than 500 µV could not be observed in Figure 7 because the floor noise was approximately 1 mV in that experiment. The amplitude characteristics are the same as the V RMS characteristics, and the distribution of the time constants is the same for all conditions [60]. Figure 20 shows the frequency of RTN with two, three, and more than three states in 18,048 MOSFETs.…”

“…Increasing I DS increases electron density in the channel, and the electron density at the source of MOSFETs with W D < W S is less than that with W S < W D . These characteristics indicate that the influence of a charged trap reduces at a high carrier density condition [39,60,62]. This means that the electron density and the location in the channel are important factors affecting RTN characteristics.…”

“…RTN characteristics were evaluated for various V DS using rectangular and trapezoidal MOSFETs. density condition [39,60,62]. This means that the electron density and the location in the channel are important factors affecting RTN characteristics.…”

“…These data imply that the noise strength depends heavily on operation conditions, which means that the location and electron density in a channel are critical for RTN generation. density condition [39,60,62]. This means that the electron density and the location in the channel are important factors affecting RTN characteristics.…”