CMOS image sensor columns share 2×2 pixel cells and pixel arrays

Abstract

The present invention relates to a column sharing 2×2 pixel unit and a pixel array of a CMOS image sensor. Four pixels are arranged to form a 2×2 pixel array acting as a pixel unit. In each pixel unit, a front column of two pixels and a back column of two pixels each share a selection transistor, a source follower transistor, a reset transistor, and a floating active region in the column. In the two-dimensional pixel array of the CMOS image sensor, for metal connection lines, two layers of metal lines are used for connection, only a 0th layer metal line and a 1st layer metal line are used as device control lines to collect image information, but a 2nd or higher layer metal line is not used as a device control line, so that the height of the medium on the Si surface of a photodiode is decreased, and more light can enter the photodiode, so as to increase the light utilization efficiency and conversion gain of a small-area-pixel sensor, thereby increasing the sensitivity and effectively improving the image quality of the small-area-pixel image sensor.

Description

technical field [0001] The invention relates to a CMOS image sensor, in particular to a CMOS image sensor column sharing 2×2 pixel units and a pixel array. Background technique [0002] Image sensors are already widely used in digital cameras, mobile phones, medical devices, automobiles and other applications. In particular, the rapid development of CMOS (Complementary Metal Oxide Semiconductor) image sensors has made people have higher requirements for low power consumption, small size, and high resolution image sensors. [0003] The CMOS image sensor columns in the prior art share the arrangement of the 2×2 pixel unit structure. Taking 4T2S (four transistors and two pixels shared) as an example, due to the dependence on the structural characteristics of the pixels themselves, the pixel array generally requires the first layer Metal, second-level metal and third-level metal are used as device interconnection lines, and multiple rows or columns of first-level metal, second-...

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Problems solved by technology

[0005] Due to the small photosensitive area and low sensitivity of the small-area pixel sensor, the information transmitted in dark light is not clear enough

Especially when the first layer of metal, the second layer of metal and the third layer of metal are used as device interconnection lines, the dielectric height on the surface of the photodiode Si (silicon) is relatively high, and the metal lines block part of the light from entering the photodiode; Moreover, the metal line connecting the floating active area to the gate of the source follower transistor is close to the power supply metal line, and the parasitic capacitance of the floating active area is large, resulting in a small amplitude (conversion gain) for converting signal electrons into signal voltage

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