Back-Side Illumination CMOS Optical Black Pixel Charge Transmission
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Solution Overview
Problem
Back side illumination CMOS image sensors face challenges in accurately detecting the black level reference value due to diffraction of long-wavelength light beams, leading to potential coloring defects in images, as the structure allows more light to be incident on the optical black pixel region, causing false recognition and instability in the dark signal.
Innovation Solution
Incorporating a transmission channel region in the optical black pixel region, which is shielded by a light shielding film, to transmit charges from the semiconductor substrate to an outside area, using an N-type region that does not touch the photoelectric conversion element, and forming a potential gradient to direct charges to a dummy pixel region, thereby reducing light incidence and stabilizing the black level reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a back side illumination CMOS image sensor is used to improve sensitivity, then sensitivity is improved, but long-wavelength light beams are prone to diffract and enter the OB region causing black level false recognition
Solution Approach 1:
The patent divides the optical black pixel region into two functional parts: a photoelectric conversion element that detects long-wavelength light beams, and a transmission channel region that allows generated charges to escape to the Nsub region. This segmentation enables the OB region to maintain dark signal reference functionality while reducing the impact of diffracted light beams on black level accuracy.
Solution Approach 2:
The patent introduces an Nsub region (N-type substrate region) as an intermediary escape route for charges generated in the OB region. This Nsub region acts as a mediator that captures and redirects charges away from the photodiode, preventing false black level signals while maintaining the sensitivity improvements of back side illumination sensors.
2Use of energy by moving object
If the photoelectric conversion region thickness is reduced to improve sensitivity, then sensitivity is improved, but light beams are repeatedly reflected among Si-wiring layer interface causing more long-wavelength light to enter the OB region
Solution Approach 1:
The patent converts the harmful effect of repeated light beam reflections into a beneficial outcome by strategically placing the Nsub region to capture charges generated by these reflections. Instead of trying to eliminate the reflections, the design uses them to generate charges that are then directed to the Nsub region, preventing false black level signals while maintaining sensitivity.
3Object-affected harmful factors
If the area of the photoelectric conversion region in the OB pixel is reduced to reduce sensitivity to light beams, then light incidence is reduced, but electrons generated in the P-type region cannot escape to the Nsub region and flow into the photodiode causing instability
Solution Approach 1:
The patent solves the charge escape problem by introducing a vertical dimension - the Nsub region extending into the substrate. Instead of relying solely on horizontal charge movement that is blocked by reduced photoelectric conversion area, charges can escape vertically into the Nsub region, maintaining stability even with reduced light-sensitive area.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces the impact of diffraction-induced light on the optical black pixel region, allowing for more accurate detection of the black level reference value and minimizing image defects caused by intense incident light, thereby enhancing the robustness of the imaging element against light beams.
Implementation Method 1
a transmission channel region provided in an optical black pixel region shielded from light beams from an outside of a semiconductor substrate by a light shielding film, for transmitting a charge existing inside the semiconductor substrate of the optical black pixel region to an outside of the optical black pixel region
Implementation Method 2
optical black pixel region shielded from light beams from an outside of a semiconductor substrate by a light shielding film
Implementation Method 3
an output signal from the OB pixel serves as a dark signal reference
Data Source
AI summary
There is provided an imaging element including a transmission channel region provided in an optical black pixel region shielded from light from an outside of a semiconductor substrate by a light shielding film, for transmitting a charge existing inside the semiconductor substrate of the optical black pixel region to an outside of the optical black pixel region.