Research progress of laser dazzle and damage CMOS image sensor (invited)

  Significance  Complementary Metal Oxide Semiconductor (CMOS) image sensors are currently the most mainstream solid-state image sensors. They have the characteristics of low power consumption, high integration, and fast imaging. In the past decade, breakthroughs have been continuously made in their performance, surpassing Charge Coupled Device (CCD) image sensors in market share and product iteration speed. It is widely used in the fields such as digital cameras, security monitoring equipment, mobile phones, drones, medical detection, and autonomous driving. As the core component of an optoelectronic imaging system, image sensors strongly absorb laser energy within their working wavelength, making them more susceptible to laser damage compared to other components of the optoelectronic system. However, the new back side illumination CMOS and stacked CMOS have significant structural differences from traditional front side illumination CMOS image sensors, and their ability to resist laser interference and damage has been greatly improved. Therefore, the laser interference effect and damage mechanism of CMOS image detectors have received widespread attention from scholars at home and abroad.

  Progress  Firstly, the structure and working principle of CMOS image sensor according to its development history are introduced. The pixel structure of CMOS has evolved from passive pixels to active pixels, where each pixel can independently collect, amplify, and output signals. SiO₂ deep trench isolation (DTI) structure (Fig.3(d)) is used between pixels for crosstalk suppression. The chip structure of CMOS has evolved from front illuminated to back illuminated and stacked, and the position of the metal wiring layer has buried deeper, making it more difficult to cause destructive damage. On this basis, the weaknesses of CMOS image sensor in the process of laser irradiation are briefly analyzed. CMOS uses a correlated double sampling (CDS) circuit to output signals, which uses the difference between two signals to output, and interfering with both signals causes pixel oversaturation; The use of the same column line to transmit the reference signal of a column of pixels provides the possibility of large-scale crosstalk. The damage at different stages is related to the depth of laser action. It can be concluded that the key to causing large-scale damage to CMOS image sensors is the severe damage to the internal circuit layer.　　CMOS image sensor is used more and more widely. More attention has been paid to the experimental study of laser-induced dazzle and damage of CMOS. The evaluation methods of interference and the main measurement methods of damage threshold are summarized. The representative measurement results of interference and damage threshold are summarized (Tab.1-2). By comparing the results of interference, the conditions of oversaturation and crosstalk are summarized, and the conclusion is verified that the above-mentioned CDS circuit is susceptible to interference. Compared with CCD, CMOS has better anti-damage ability, especially the back-illuminated CMOS, which is difficult to cause large area damage. This is because the back-lit CMOS circuit layer is deeper, above a thicker layer of silicon-based material, forming a certain inherent protective layer. With the wide application of backlit and stack CMOS chips, how to improve the damage efficiency of laser-illuminated CMOS chips is an urgent problem to be solved in the next research.　　Finally, the development status and prospects of using new laser systems to improve the damage ability of CMOS image sensors are discussed. The composite laser can be made up of two pulses with different parameters. The ablation and damage of the composite laser on the single material target has been well studied. If the laser parameters are matched properly, the absorption rate of laser energy can be improved effectively. It has been proved that the composite laser can improve the efficiency of damaged CMOS to some extent, but the effect is limited. To further improve the laser damage efficiency, we can consider to further increase the adjustable parameters of the laser, the combination of three or more pulses into the pulse string form.

  Conclusions and Prospects   CMOS image sensors are booming, which have become the most mainstream image sensors. As an important countermeasure, the research of laser jamming and damage CMOS image sensor needs to be further explored. The purpose of this paper is to provide some references for the future research of laser jamming and damage CMOS, and the idea of using the new laser system to improve the damage efficiency is proposed.