Triangular Macropixel Imager for High Fill Factor
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Solution Overview
Problem
In image sensors, particularly CMOS image sensors, the reduction in pixel pitch leads to a smaller pixel fill factor due to increased consumption of area by active circuit elements and metal interconnects, which affects image quality and size requirements, especially in medical applications where high-quality images are needed from a small chip size.
Innovation Solution
The use of backside illuminated image sensors with a color filter array of non-rectangular, triangular macropixels, which include three micropixels arranged on an X, Y grid, allowing for a greater fill factor by reducing the area devoted to non-photosensitive elements and enabling larger photosensitive elements, thus improving image quality and full well capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel pitch is reduced to increase resolution, then image sensor can capture more detail, but pixel fill factor decreases because active circuit elements and metal interconnect consume increasing proportion of area
Solution Approach 1:
The patent transitions from planar 2D pixel arrangement to a 3D stacked architecture where photosensitive elements are positioned at different depths (z-dimension) within the substrate. This vertical stacking allows multiple photosensitive regions to occupy the same footprint area, effectively increasing the photosensitive area without increasing the pixel pitch, thereby resolving the contradiction between high resolution and fill factor.
Solution Approach 2:
The patent implements nested photosensitive elements where multiple photosensitive regions are positioned one above another within the same pixel footprint. The first photosensitive element is positioned at a first depth and the second photosensitive element at a second depth, creating a nested configuration that maximizes the use of vertical space within each pixel, thereby increasing effective fill factor while maintaining small pixel pitch.
2Productivity
If photosensitive region size is reduced to fit more pixels on chip, then pixel pitch can be reduced, but light sensitivity and full well capacity deteriorate
Solution Approach 1:
By introducing the depth dimension (z-axis) into the pixel structure, the patent allows each pixel to contain multiple photosensitive elements stacked vertically. This enables the pixel density to increase in the planar direction while each individual photosensitive element maintains sufficient size for good light sensitivity, as the effective photosensitive area is distributed across multiple depth layers rather than compressed in a single plane.
Solution Approach 2:
The patent divides each pixel into multiple segmented photosensitive elements positioned at different depths. Each segment captures light independently, and their signals are combined to produce the final pixel output. This segmentation allows the total photosensitive area to be distributed across multiple smaller elements stacked vertically, maintaining high pixel density while preserving the light sensitivity characteristics of individual photosensitive regions.
3Adaptability or versatility
If more area is devoted to active circuit elements and interconnect, then pixel functionality is enhanced, but photosensitive area is reduced
Solution Approach 1:
The patent relocates active circuit elements from the planar pixel area to the vertical dimension by positioning them in deeper regions of the substrate below the photosensitive elements. This vertical separation allows the photosensitive area to occupy the upper layers with maximum planar coverage, while circuit elements are accommodated in the lower layers, effectively decoupling the area requirements of photosensitive regions and active circuits.
Solution Approach 2:
The patent inverts the traditional arrangement by placing photosensitive elements above active circuit elements in the vertical stack, rather than having circuits above photosensors. This inverted configuration allows light to incidently reach the photosensitive elements without being blocked by overlying circuit structures, maximizing photosensitive area while still providing full circuit functionality below.
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 enhances the fill factor, allowing for larger photosensitive elements and increased full well capacity, resulting in improved image quality and flexibility in color proportion assignment, optimizing image sensors for various applications.
Implementation Method 1
a color filter array of non-rectangular, triangular macropixels, which include three micropixels arranged on an X, Y grid
Implementation Method 2
the majority of photon absorption occurs near the backside silicon surface
Implementation Method 3
photosensitive elements and the photosensitive apertures should be as large as possible
Data Source
AI summary
A color pixel array includes a plurality of micropixels. Each micropixel includes a photosensitive element and a filter element optically aligned with the photosensitive element such that incident light passes through the filter element prior to reaching the photosensitive element. The micropixels are organized into triangular macropixels that each includes multiple micropixels. A perimeter shape of each of the triangular macropixels forms a triangle. The triangular macropixels have a repeating pattern across the color pixel array.