Four-tube active pixel of rapid charge transfer and making method thereof

Abstract

The present invention belongs to the field of integrated circuit design and integrated circuit processes in microelectronics, and relates to a 4 transistors active pixel sensor with rapid charge transfer. Included are manufacturing a photodiode, a transmission tube, a reset tube, a source follower and a strobe tube on a P-type substrate, wherein the N region of the photodiode includes a first N-type injection layer and a second N-type injection layer provided thereon with a relatively low doping concentration, and two N-type injection layers have overlapped areas with the pattern of the polysilicon gate of the transmission tube; providing a P-type semiconductor injection layer with uneven doping concentration at the overlapped area and the under-gate area of the transmission tube, with the doping concentration thereof being highest at the overlapped area; the doping of the polysilicon gate of the transmission tube is N-doping at the overlapped area side and N+doping at the non-overlapped area; and providing a layer of clamping layer between the non-overlapped area of the N region of the photodiode and the silicon surface. Provided at the same time is a manufacturing method for the active pixel mentioned above. The pixels in the present invention can obtain rapid and tailless charge transfer.

Description

technical field [0001] The invention relates to the field of integrated circuit design and integrated circuit technology of microelectronics, in particular to a four-transistor active pixel sensor (4transistors active pixel sensor, 4T APS) with fast charge transfer and a manufacturing method thereof. Background technique [0002] With the continuous reduction of the standard CMOS logic process and the continuous improvement of the CMOS image sensor (CMOS Image Sensors, CIS) manufacturing process, the CMOS image sensor continues to exert its advantages over the CCD image sensor in terms of integrability, power consumption, and random addressing. Relative advantages, becoming the mainstream device in the field of solid-state image sensors. Pinned-Photodiode Four Transistors-Active Pixel Sensor (PPD 4T-APS) based on clamping diodes has the characteristics of low dark current, can eliminate reset noise and low image smearing, and is currently the main pixel used in CIS structur...

AI Technical Summary

Problems solved by technology

The above-mentioned traditional PPD 4T-APS faces serious bottlenecks in this respect: on the one hand, due to the conversion of charges into voltages and the corresponding conversion node reset process, active pixels need to perform correlated double sampling of the FD reset voltage and the FD light-induced voltage , so that the fixed pattern noise and reset noise can be eliminated to output a low-noise readout signal equivalent to a CCD pixel

Compared with the simple charge transfer between CCD pixels, at the same frame readout rate, the time Ttf for PPD 4T-APS charge transfer is shorter than that of CCD pixels; on the other hand, since CMOS pixels are compatible with standard CMOS processes, The reset voltage of the TG gate and FD is much lower than that of the CCD pixel, the potential well depth difference ΔΦ from the PD to the FD is small, and the electric field pointing to the TX direction at the edge of the PD far away from the TX is weak, resulting in a sense of The speed of the generated charge Q moving towards TX slows down

Therefore, under the condition of the same PD size and frame readout rate, it is more difficult for PPD 4T-APS pixels to achieve rapid and complete transfer of induced charges than CCD pixels, and it is easier to leave residual charges in PDs.

This kind of charge residue will not only bring serious image smearing, but also further deteriorate the random noise of pixels, which ultimately limits the application of CMOS image sensors in high-end imaging fields.

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