CMOS Image Sensor Color Filter Planarization
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Solution Overview
Problem
CMOS image sensors face limitations in light sensitivity due to the presence of a planarization layer, which increases the traveling distance of light and degrades focusing characteristics, hindering the development of compact-sized products.
Innovation Solution
A CMOS image sensor design that eliminates the need for a planarization layer by planarizing the color filter layer itself, allowing microlenses to be directly formed on an equalized surface, thereby reducing light travel distance and enhancing image characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a planarization layer is added to the CMOS image sensor, then the surface flatness is improved, but the light travel distance increases and light sensitivity deteriorates
Solution Approach 1:
The patent removes the planarization layer from the CMOS image sensor structure. By extracting this unnecessary layer, the light travel distance is reduced and light sensitivity is improved while maintaining surface flatness through alternative means (direct formation of microlenses on the color filter layer surface).
Solution Approach 2:
The patent applies local planarization by forming microlenses directly on the color filter layer surface, which provides localized surface flatness where needed (at the microlens formation area) without requiring a global planarization layer that would increase light travel distance across the entire sensor.
2Use of energy by moving object
If the photo-sensing portion area is increased to improve fill factor, then light sensitivity is improved, but the logic circuit portion area is reduced
Solution Approach 1:
The patent utilizes the vertical dimension by forming microlenses that protrude from the color filter layer surface. This three-dimensional structure allows light focusing without increasing the horizontal footprint, thereby maintaining both photo-sensing area and logic circuit area while improving light sensitivity.
3Use of energy by moving object
If microlenses are formed on a non-planar surface, then light focusing is improved, but manufacturing precision deteriorates
Solution Approach 1:
The patent performs preliminary planarization of the color filter layer surface before forming the microlenses. This preliminary action creates a flat base surface that ensures precise microlens formation, while the microlenses themselves maintain the light focusing capability by protruding from this planar surface.
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 approach improves image characteristics by minimizing light travel distance and focusing issues, leading to enhanced light sensitivity and performance in compact-sized imaging devices.
Implementation Method 1
the incident light, striking the surface of the convex structure of the microlens while in parallel to the optical axis of the microlens, is refracted by the microlens according to the curvature of the convex structure. The incident light is thereby focused at a predetermined point along the optical axis.
Data Source
AI summary
A CMOS image sensor and method for fabricating the same improve image characteristics by eliminating the thickness of a planarization layer. The CMOS image sensor includes a semiconductor substrate; a plurality of active devices, provided in a predetermined surface of the semiconductor substrate, for generating electrical charges according to an amount of incident light; an insulating interlayer formed on an entire surface of the semiconductor substrate including the plurality of active devices; a color filter layer formed on the insulating interlayer, the color filter layer comprised of red, green, and blue color filter patterns for respectively filtering light according to wavelength, the color filter patterns arranged to correspond to the plurality of active devices; and a plurality of microlenses formed on the color filter layer, wherein the color filter layer is planarized so that each color filter pattern of the color filter layer is imparted with an equal height for receiving the plurality of microlenses.