Image Sensor Vertical Electrodes Parasitic Charge Isolation
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Solution Overview
Problem
Existing pixel structures with vertical electrodes in global shutter control mode are sensitive to spurious node sources, particularly due to parasitic charge diffusion from high-wavelength light rays, which can alter the stored information during extended signal storage periods.
Innovation Solution
The image sensor design incorporates a semiconductor substrate with a photosensitive area, storage area, and reading area, featuring a first vertical insulated electrode and insulating elements such as an insulating layer and a doped region to reduce charge transfer depth, preventing parasitic charges from reaching the storage area by using an insulating layer and a vertical insulating wall to limit the charge transfer area to a depth smaller than the electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If vertical electrodes are used for global shutter control, then the sensor can simultaneously expose all pixels and store signals, but the sensor becomes sensitive to spurious node sources and parasitic charge diffusion from high-wavelength light
Solution Approach 1:
An insulating layer is introduced as an intermediary element between the photosensitive area and the storage area. This insulating layer acts as a mediator that blocks parasitic charge diffusion while allowing the vertical electrode to maintain its charge transfer function, thus resolving the contradiction between global shutter capability and sensitivity to spurious charges
Solution Approach 2:
The charge transfer path is segmented into distinct regions by the insulating layer, which creates a barrier that divides the continuous charge diffusion path. This segmentation allows the electrode to transfer intended charges while blocking parasitic charges from high-wavelength light, maintaining global shutter operation without spurious signal contamination
2Productivity
If the electrode extends deep into the substrate to enable charge transfer, then charge transfer efficiency is improved, but parasitic charges from high-wavelength light can reach the storage area
Solution Approach 1:
The insulating layer serves as a mediator that allows deep electrode extension for efficient charge transfer while blocking parasitic charges. It mediates between the need for deep electrode penetration and the need to prevent spurious charge collection, maintaining both transfer efficiency and signal accuracy
Solution Approach 2:
The insulating layer provides localized insulation properties at the electrode-substrate interface, creating a region with different electrical characteristics. This local quality change allows the electrode to maintain good electrical contact for charge transfer while the insulating layer locally blocks parasitic charge diffusion to the storage 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 design effectively isolates the storage area from parasitic charge diffusion, reducing noise and artifacts in the final image by preventing photogenerated charges from high-wavelength light from being collected by the storage area, thereby maintaining accurate image storage and retrieval.
Implementation Method 1
a layer of an insulating material extending at least under the entire surface of the photosensitive area and under the entire surface of the storage area
Implementation Method 2
an insulating wall extending vertically inside of or opposite a lower portion of said opening, or under said opening, so that the depth of the charge transfer area is smaller than the depth of said electrode
Implementation Method 3
a photosensitive area comprising a first well of a conductivity type opposite to that of the substrate
Data Source
AI summary
An image sensor arranged inside and on top of a semi-conductor substrate having a front surface and a rear surface, the sensor including a plurality of pixels, each including: a photosensitive area, a reading area, and a storage area extending between the photosensitive area and the reading area; a vertical insulated electrode including an opening of transfer between the photosensitive area and the storage area; and at least one insulation element among the following: a) a layer of an insulating material extending under the surface of the photosensitive area and of the storage area and having its front surface in contact with the rear surface of the electrode; and b) an insulating wall extending vertically in the opening, or under the opening.