Vertical Image Sensor Photodiode Circuitry Stacking
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Solution Overview
Problem
The reduction in photodiode size for increasing pixel density in image sensors leads to reduced light reception area, causing image quality issues due to diffraction and charge sharing phenomena, resulting in sensitivity reduction and image errors.
Innovation Solution
A vertical integration of a photodiode and circuitry is achieved by forming a high concentration first conduction type region and electrical junction on a substrate, allowing efficient electron transfer and improved image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the photodiode size is reduced to increase pixel density, then the number of pixels increases, but the light receiving area is reduced causing image quality degradation
Solution Approach 1:
The patent transitions from a planar photodiode structure to a vertical stacked structure, moving the light receiving function to a different spatial dimension. The photodiode is positioned above the readout circuitry in the vertical direction, allowing light to be received from the top surface while circuitry operates below, effectively decoupling pixel density from light receiving area constraints.
Solution Approach 2:
The patent implements a nested configuration where the readout circuitry is integrated beneath the photodiode structure. The circuitry components (transistors, interconnections) are positioned in the lower layers while the photodiode occupies the upper layer, creating a vertical nesting arrangement that maximizes space utilization and maintains full light receiving area.
2Reliability
If heavily doped N-type regions are used for source and drain to ensure proper transistor operation, then transistor functionality is maintained, but charge sharing phenomenon occurs reducing sensitivity and causing image errors
Solution Approach 1:
The patent modifies the doping parameters in the photodiode region by introducing a first doped region with first conduction type (opposite to the N-type source/drain) and a second doped region with second conduction type. This parameter change in doping type and concentration creates depletion regions that prevent charge sharing between adjacent photodiodes while maintaining proper transistor operation through the electrical junction region.
3Quantity of substance
If photodiode area is reduced, then pixel density increases, but diffraction effects increase reducing the number of incident photons
Solution Approach 1:
By stacking the photodiode vertically above the circuitry rather than expanding horizontally, the patent maintains a large effective light receiving area that captures sufficient photons despite high pixel density. The vertical arrangement allows each pixel to maintain its full light gathering capability while increasing the number of pixels per unit chip 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 image quality, increases sensitivity, and minimizes manufacturing costs while allowing for more complex pixel circuitry, achieving a fill factor close to 100% and improved performance.
Implementation Method 1
an image sensor is a semiconductor device for converting an optical image into an electrical signal
Implementation Method 2
a high concentration first conduction type region on and/or over the electrical junction region; and a photodiode on and/or over the circuitry
Data Source
AI summary
An image sensor includes a circuitry, a substrate, an electrical junction region, a high concentration first conduction type region, and a photodiode. The circuitry includes a transistor and is formed on and/or over the substrate. The electrical junction region is formed in one side of the transistor. The high concentration first conduction type region is formed on and/or over the electrical junction region. The photodiode is formed over the circuitry.