Vertical Pixel Sensor Layout for Light Sensitivity and Fast Switching
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Solution Overview
Problem
As CMOS image sensors shrink in size, the horizontal arrangement of photodiode and floating diffusion regions leads to reduced light sensitivity due to smaller photodiode areas, and increased switching delays due to smaller gate switching areas.
Innovation Solution
A vertically stacked arrangement of photodiode and floating diffusion regions, with the transfer gate surrounding at least a portion of both regions, increases the photodiode area for light collection and enhances gate switching control, reducing switching delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the photodiode and floating diffusion regions are arranged horizontally, then the layout is simple and manufacturing is easier, but the photodiode area decreases leading to reduced light sensitivity
Solution Approach 1:
The patent transitions from a horizontal two-dimensional arrangement to a vertical three-dimensional stacked arrangement. The photodiode region, transfer gate, and floating diffusion region are stacked vertically, allowing the photodiode to maintain a larger horizontal area for light collection while the other components occupy the vertical dimension, thereby resolving the contradiction between manufacturing simplicity and light sensitivity.
2Volume of moving object
If the photodiode and floating diffusion regions are arranged horizontally, then the device structure is compact, but the gate switching area decreases leading to increased switching delays
Solution Approach 1:
By stacking the transfer gate vertically over the photodiode region and having it surround the floating diffusion region in three dimensions, the gate switching area is substantially increased without expanding the horizontal pixel footprint. This vertical configuration allows the gate to control a larger area, reducing switching delays while maintaining device compactness.
3Area of moving object
If the photodiode region area is reduced to shrink pixel size, then the overall sensor size decreases, but light sensitivity and quantum efficiency deteriorate
Solution Approach 1:
The vertical stacking configuration allows the photodiode region to maintain a larger horizontal area for photon collection while the overall pixel size is reduced through efficient vertical integration of other components. The transfer gate surrounds the floating diffusion region in three dimensions, maximizing space utilization and enabling smaller pixel dimensions without compromising the photodiode's light-sensitive area.
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 light sensitivity and quantum efficiency while allowing for a reduction in overall pixel sensor size, improving performance by increasing the area for photon collection and reducing noise and light leakage.
Implementation Method 1
a photodiode region configured to convert photons of incident light into a photocurrent of electrons
Data Source
AI summary
A pixel sensor may include a vertically arranged (or vertically stacked) photodiode region and floating diffusion region. The vertical arrangement permits the photodiode region to occupy a larger area of a pixel sensor of a given size relative to a horizontal arrangement, which increases the area in which the photodiode region can collect photons. This increases performance of the pixel sensor and permits the overall size of the pixel sensor to be reduced. Moreover, the transfer gate may surround at least a portion of the floating diffusion region and the photodiode region, which provides a larger gate switching area relative to a horizontal arrangement. The increased gate switching area may provide greater control over the transfer of the photocurrent and/or may reduce switching delay for the pixel sensor.