Image Sensor Anti-Reflection Board Stabilizes Black Level
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Solution Overview
Problem
CMOS image sensors experience light leakage phenomena in optical black regions, leading to distorted black levels and degraded image quality due to reflections and photoelectric effects, which affect the accuracy of image signals.
Innovation Solution
The implementation of an image sensor design that includes an anti-reflection board and light shielding film, with a metal board and anti-reflection coating film, such as tantalum or nitrogen-containing tantalum, to prevent light leakage by forming a structure that shields the optical black region and applies a positive voltage to the metal board, combined with a drain structure to capture excessive electrons and an anti-reflection coating on the substrate's lower surface to absorb stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light shielding film is used to block incident light in the optical black region, then the black level can be maintained, but light leakage occurs due to reflections from wire layers and total reflection at the substrate lower surface
Solution Approach 1:
An anti-reflection board is introduced as an intermediary component between the active region and the optical black region. This board includes a metal board with an anti-reflection coating film that absorbs or blocks reflected light and stray light before they reach the second pixels, thereby preventing light leakage without compromising the black level stability provided by the light shielding film.
Solution Approach 2:
The solution addresses light leakage not only from the upper surface (where the light shielding film is located) but also from the lower surface of the substrate. By applying an anti-reflection coating film on the lower surface of the substrate and introducing an anti-reflection board in the intermediate region, the patent blocks light leakage paths from multiple dimensions, particularly addressing total reflection at the lower substrate surface.
2Area of stationary object
If the optical black region is positioned adjacent to the active region for compact design, then device area is reduced, but light leakage through the boundary between active region and optical black region occurs
Solution Approach 1:
The anti-reflection board serves as a mediator positioned between the active region and the optical black region. It includes a metal board with anti-reflection coating that intercepts and absorbs light that would otherwise leak through the boundary between these regions, enabling compact design while preventing light leakage at the interface.
3Ease of operation
If wire layers are used to connect pixels, then electrical connectivity is achieved, but they cause reflections that lead to light leakage in the optical black region
Solution Approach 1:
The anti-reflection board with metal coating acts as an intermediary that absorbs or blocks light reflected from the wire layers. By positioning this board between the wire layers and the optical black region, it prevents the reflected light from reaching the second pixels, thereby eliminating the harmful effect of wire-induced light leakage while maintaining electrical connectivity.
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 design effectively stabilizes the black level by reducing light leakage and distortion, thereby improving the quality of displayed images by providing accurate reference signals for image processing.
Implementation Method 1
an anti-reflection board formed between the substrate and the light shield film and between the first pixels and the second pixels to prevent the light from being reflected toward the second pixels
Implementation Method 2
a light shielding film formed above the substrate... the light shielding film covers an optical black region including the first and second regions
Implementation Method 3
a light 151 passes through a boundary between the active region and the optical black region to reach the second pixels 115 by reflections due to wire layers 120 and 130. Also, a light 152 may reach the second pixels 115 by total reflection at a lower surface of the substrate 110. The lights 151 and 152 may distort the black level by causing a photoelectric effect to the second pixels 115
Data Source
AI summary
An image sensor includes a substrate, an anti-reflection board and a light shielding film. The substrate includes first pixels to receive a light, and second pixels to provide a black level compensation. The first pixels are formed in an active region and the second pixels are formed in a first region spaced apart from the active region in a row direction. The anti-reflection board is formed in a second region above the substrate, and the second region is between the active region and the first region. The light shielding film is formed above the anti-reflection board, and the light shielding film covers an optical black region including the first and second regions. Therefore, the image sensor may be used in a CCD type image sensor and a CMOS type image sensor to provide a stabilized black level, thereby improving a quality of a displayed image.