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The Past and Present of Image Sensor Technology

The Past and Present of Image Sensor Technology

1. Application development of image sensor technology

Historically, CCD image sensors and CMOS image sensors appeared almost simultaneously in the 1960s. From 1965 to 1970 (the 1970s), companies such as IBM and Fairchild developed optoelectronic and bipolar diode arrays. In 1970, the CCD image sensor was invented in Bell Labs, and relying on the high quantum efficiency, high sensitivity, low dark current, high consistency, and low noise of the CCD image sensor, it has always become the dominant image sensor market.


Compared with CCD image sensors, CMOS image sensors have the advantages of low power consumption, low operating voltage, on-chip integrated functions, and low price. However, in the early days of CMOS image sensors, due to relatively poor performance and large pixel size, they did not get a good market response. Later, with the continuous improvement of Very Large Scale Integration technology (VLSI) and CMOS process level, sensor CMOS gradually began to show the advantages that CCD image sensors did not have, and their market share in the field of image sensors gradually expand.


2. CMOS image sensor technology becomes mainstream

The development of CMOS image sensor and image sensor technology mainly has three stages, namely passive pixel sensor(PPS), active pixel sensor and digital pixel sensor.


In the early 1990s, the passive pixel CMOS image sensor entered the market as the first-generation CMOS image sensor. Compared with the initial CMOS image sensor, the PPS CMOS image sensor mainly improved the signal-to-noise ratio. After that, APS CMOS image sensors appeared as the second-generation CMOS image sensors. Compared with PPS CMOS image sensors, they mainly improved readout noise and data readout speed. For a long time afterwards, APS CMOS image sensors was the research focus of CMOS image sensors.


At the end of the 20th century, Stanford University in the United States proposed the DPS CMOS image sensor, which uses a pixel-level analog-to-digital converter and storage unit to directly convert the captured light signal into a digital signal output, aiming to solve the shortcomings of CCD image sensor in processing dynamic range and color authenticity, and minimize the attenuation and interference of the signal in the arrangement so as to improve the image quality.


At present, CMOS image sensors used in cameras are mainly APS CMOS image sensors and DPS CMOS image sensors. Relatively speaking, APS CMOS image sensor technology is relatively mature, and DPS CMOS image sensor technology is increasingly becoming the focus of research. Thanks to the continuous development of very large scale integrated circuit technology (VLSI) and CMOS process level, in imaging applications, the quantum efficiency, fill factor and other imaging performance of CMOS image sensors are gradually comparable to CCD image sensors, occupying more market share, nowadays smart phone cameras mostly use CMOS image sensors. In imaging fields such as underwater detection and space-to-ground remote sensing, CMOS image sensors may also replace CCD image sensors, and gradually become the main choice of image sensors in most imaging fields.

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