Image Sensor Pixel Sharing Output Lines to Maximize Aperture Ratio
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Solution Overview
Problem
CMOS image sensors with small pixel pitches face reduced sensitivity due to metal lines that shield photo diodes, affecting the aperture ratio and overall pixel performance.
Innovation Solution
The image sensor design shares output lines and supply voltage lines between adjacent photo diodes in a horizontal direction, minimizing the number of metal lines and maximizing the aperture ratio, thereby enhancing pixel sensitivity for pitches of 1.75 μm or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pitch of a pixel is reduced to increase the number of pixels, then the pixel density increases, but the aperture ratio of the photo diode decreases due to shielding by metal lines
Solution Approach 1:
Adjacent photo diodes share common metal lines (output lines and supply voltage lines) to reduce the total number of metal lines in the pixel array. This merging approach minimizes the shielding effect on photo diodes while maintaining electrical connectivity, thereby preserving aperture ratio even as pixel pitch is reduced
Solution Approach 2:
Metal lines are designed to serve multiple adjacent photo diodes simultaneously. Output lines and supply voltage lines function as shared resources for multiple photo diodes, reducing the overall metal line density and minimizing their harmful shielding effect on the aperture ratio
2Object-affected harmful factors
If the number of metal lines is reduced to increase aperture ratio, then photo diode sensitivity improves, but the complexity of signal routing increases
Solution Approach 1:
Multiple photo diodes share common output lines and supply voltage lines, reducing the total number of metal lines required. This merging strategy maintains photo diode sensitivity by minimizing metal line shielding while managing signal routing through systematic sharing patterns
Solution Approach 2:
The pixel array is divided into units where adjacent photo diodes share metal lines. This segmentation approach organizes the routing complexity into manageable units, making the shared metal line structure systematic and implementable
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 configuration effectively secures a sufficient aperture ratio for photo diodes, enhancing the sensitivity of small-sized pixels by reducing the impact of metal lines and improving the image sensor's performance.
Implementation Method 1
CMOS image sensors are devices that convert optical images into electrical signals. A CMOS image sensor may convert signal electrons generated in response to incident light into a voltage signal.
Data Source
AI summary
An image sensor includes a plurality of unit pixels. Each unit pixel has a photo diode for sensing external light to generate photo charges. A transfer transistor is connected to the photo diode for storing the photo charges generated in the photo diode into a floating diffusion region when being turned-on. An amplification transistor amplifies the photo charges stored into the floating diffusion region. A select transistor, connected to the amplification transistor, performs a switching operation. An output line, extended in a column direction, outputs the photo charges in accordance with the switching operation of the select transistor. The photo diode may be formed in such a manner to share the output line with its adjacent photo diode in a horizontal direction, so that the photo charges generated in the photo diode and its adjacent photo diode are outputted through the output line.