Forming method of CMOS image sensor transfer transistor

Abstract

The invention provides a forming method of a CMOS image sensor transfer transistor. The forming method comprises the following steps: forming a photodiode and a floating diffusion region; forming at least one transfer transistor; correspondingly depositing p-type doped polycrystalline silicon above the photodiode to serve as a transfer transistor grid electrode or a part of the grid electrode; and when the photodiode is in a charge accumulation state, determining that the voltage applied to the grid electrode of the transfer transistor is greater than or equal to 0V. When the p-type doped transfer transistor grid electrode is adopted and the photodiode is in a charge accumulation state, the pinning effect can be achieved only by applying a voltage of 0V or more than 0V, a large capacitor and an additional circuit structure do not need to be adopted, the area is saved, the process cost is reduced, and meanwhile the stability of a voltage signal is high.

Description

technical field [0001] The invention relates to the technical field of image sensors, in particular to a method for forming a transfer transistor of a CMOS image sensor. Background technique [0002] As a device unit that converts optical signals into digital electrical signals, CMOS image sensors are widely used in various emerging fields such as smartphones, tablet computers, automobiles, and medical care. As the core module of the image sensor, the pixel array is mainly composed of photodiodes, transfer transistors, reset transistors, and source follower transistors. Among them, the transfer transistor is located between the photodiode and the floating diffusion region to realize the switching function. The role of the floating diffusion region is to collect electrons converted by the photodiode, and convert the electronic signal into a corresponding voltage signal according to its conversion gain capability. [0003] In the prior art, the transfer transistor uses an n-t...

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Problems solved by technology

In the analog circuit, the negative pressure signal needs to be realized through the "charge pump". This structure has the following two problems: the stability of the negative pressure signal generated by the "charge pump" is poor, and the signal and the signal in the floating diffusion area exist Coupling effect, so this structure will lead to larger output signal noise; "charge pump" needs to be realized through a large capacitor and an additional circuit structure, so it needs to occupy a larger area and increase the process cost

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