CMOS Image Sensor Light Blocking Layer Stray Noise Reduction
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Solution Overview
Problem
Conventional CMOS image sensors are susceptible to noise due to stray and undesired light beams, particularly at the boundary edges of the active pixel array, which degrades image accuracy and quality as the pixel arrays become smaller and denser.
Innovation Solution
A light blocking layer composed of thin opaque materials, such as titanium nitride, is used to cover the support feature section and peripheral areas of the CMOS image sensor, effectively blocking stray light through film patterning and etching processes, while maintaining transparency over the active light sensing section.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If semi-opaque light shielding layers are used to cover peripheral structures, then light diffraction is reduced, but the pixel arrays become more susceptible to noise as they become smaller and denser
Solution Approach 1:
The patent applies different optical properties to different regions: the light shielding layer is made opaque specifically at the boundary edges where light diffraction occurs, while remaining transparent over the active pixel array area. This localized application of opacity resolves the contradiction by targeting the harmful light diffraction at boundaries without affecting the light sensitivity of the pixel array.
Solution Approach 2:
The light shielding layer is segmented into two distinct regions: an opaque portion at the boundary edges and a transparent portion over the active pixel array. This segmentation allows the structure to simultaneously block diffracted light at boundaries while permitting useful light to reach the photodiodes, thereby reducing noise susceptibility in smaller, denser pixel arrays.
2Object-affected harmful factors
If conventional light shield layers are used, then most diffracted light is blocked, but they do not totally block incoming light and noise remains
Solution Approach 1:
The light shielding layer is made opaque specifically at the boundary edges where light diffraction occurs, while remaining transparent over the active pixel array area. This localized application of opacity resolves the contradiction by targeting the harmful light diffraction at boundaries without affecting the light sensitivity of the pixel array.
Solution Approach 2:
The patent converts the harmful effect of light diffraction at boundary edges into a beneficial structure by placing opaque light shielding material precisely at those boundary regions. This transforms the problem area into a solution, using the same boundary regions that cause diffraction as the precise location for applying the anti-diffraction shielding.
3Productivity
If pixel arrays are made smaller and denser, then device integration is improved, but noise susceptibility increases
Solution Approach 1:
The light shielding layer is made opaque specifically at the boundary edges where light diffraction occurs, while remaining transparent over the active pixel array area. This localized application of opacity resolves the contradiction by targeting the harmful light diffraction at boundaries without affecting the light sensitivity of the pixel array.
Solution Approach 2:
The light shielding layer is formed as part of the preliminary fabrication process, specifically as part of the interlayer dielectric structure before final pixel array completion. This preliminary application of light shielding prevents noise issues from developing in the first place, allowing smaller, denser pixel arrays to be integrated without suffering from increased noise susceptibility.
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
The implementation of the light blocking layer significantly reduces electrical noise by minimizing diffracted light, enhancing image sensor performance, accuracy, and production yields, leading to cost advantages and improved competitive positioning.
Implementation Method 1
A light blocking portion includes a black light filter layer and an opaque layer covering the support feature section
Implementation Method 2
The photoenergy from the light beams, upon striking the photodiode, frees electrons within the photodiode to be processed as the pixel's image data
Implementation Method 3
the incoming light beams are focused by a microlens through a color filter layer such that they converge along the focal axis of the microlens to strike the light sensing element (photodiode)
Implementation Method 4
Each pixel may include a color filter located over the light sensing element to selectively process image data by a specific color
Data Source
AI summary
A method and device is disclosed for reducing noises in CMOS image sensors. An improved CMOS image sensor includes a light sensing structure surrounded by a support feature section. An active section of the light sensing structure is covered by no more than optically transparent materials. A light blocking portion includes a black light filter layer and an opaque layer covering the support feature section. The light blocking portion may also cover a peripheral portion of the light sensing structure. The method for forming the CMOS image sensors includes using film patterning and etching processes to selectively form the opaque layer where the light blocking portion is desired but not over the active section.