Image Sensor Pixels with Vertical Charge Storage Wells
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Small image sensor pixels face a reduction in storage well capacity due to decreased doping layer areas, leading to a loss in charge storage capability, which is not effectively addressed by existing technologies.
Innovation Solution
Incorporating a p+ doped layer under the photodiode with an opening to direct photo-generated carriers into a storage well, coupled with additional doped implants and a controlled depletion region to enhance charge storage capacitance and prevent blooming and dark current generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is reduced to increase pixel density, then more pixels can be packed in the sensor, but charge storage well capacity decreases
Solution Approach 1:
The patent extends the charge storage well into the vertical dimension by creating a deep potential well that penetrates through the photodiode depletion region into the substrate. This vertical extension allows small pixels to achieve high charge storage capacity without increasing lateral pixel dimensions, effectively resolving the contradiction between pixel density and charge storage capacity.
Solution Approach 2:
The patent modifies the doping concentration parameters in the substrate region beneath the photodiode, creating a graded or selective doping profile that forms an extended potential well. By changing the doping parameters (concentration, depth, distribution), the charge storage capacity is enhanced without increasing pixel area, thus resolving the contradiction between small pixel size and high well capacity.
2Area of moving object
If doping layer area is decreased in small pixels, then pixel size is reduced, but charge storage capability is lost
Solution Approach 1:
The patent compensates for the reduced lateral doping layer area by extending the charge storage function into the vertical dimension. A deep potential well is formed that reaches into the substrate, providing sufficient charge storage volume despite the smaller lateral footprint, thus resolving the contradiction between reduced area and maintained charge storage capability.
Solution Approach 2:
The patent creates a composite doped structure combining the photodiode region with an extended substrate region having different doping characteristics. This composite structure allows the small pixel to leverage both the photodiode's charge generation and the substrate's extended charge storage, maintaining high charge storage capability despite reduced doping layer area.
3Quantity of substance
If photodiode depletion region is extended to increase charge collection, then charge storage capacity improves, but dark current increases
Solution Approach 1:
The patent applies different doping qualities to different regions: the photodiode depletion region is optimized for charge collection, while the extended substrate region beneath it is doped to create a potential well with specific electrical characteristics. This local differentiation allows the depletion region to extend for charge collection while the doped substrate region suppresses dark current through field effect, resolving the contradiction between charge storage capacity and dark current generation.
Solution Approach 2:
The patent introduces a doped substrate region as an intermediary between the photodiode and the bulk substrate. This intermediary layer serves dual functions: it extends the charge storage capacity by creating a deep potential well while simultaneously suppressing dark current through field effect and carrier sweep-out mechanisms, thus resolving the contradiction between charge storage and dark current.
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 increases the charge storage well capacity of small pixels while minimizing dark current and pixel crosstalk, enabling effective charge transfer and improved image sensing performance.
Implementation Method 1
image sensors sense light by converting impinging photons into electrons or holes that are integrated (collected) in sensor pixels
Implementation Method 2
increase the charge storage well capacity of small pixels
Implementation Method 3
coupled with additional doped implants and a controlled depletion region to enhance charge storage capacitance
Data Source
AI summary
An image sensor having small pixels with high charge storage capacity, low dark current, no image lag, and good blooming control may be provided. The high charge storage capacity is achieved by placing a p+ type doped layer under the pixel charge storage region with an opening in it for allowing photo-generated charge carriers to flow from the silicon hulk to the charge storage well located near the surface of the photodiode. A compensating n-type doped implant may be formed in the opening. Image lag is prevented by placing a p− type doped region under the p+ type doped photodiode pinning layer and aligned with the opening. Blooming control is achieved by adjusting the length of the transfer gate in the pixel and thereby adjusting the punch-through potential under the gate.