CMOS Image Sensor Indented Photodiode Junction Interface
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Solution Overview
Problem
CMOS image sensors face limitations in full well capacity due to the difficulty in controlling photodiode profiles with high ion-implant dosage, which affects dynamic range and picture quality.
Innovation Solution
The introduction of a CMOS image sensor with a photodiode structure featuring an indented p-n junction interface, including recessed portions symmetrically distributed along the gate electrode and floating diffusion region, increases the area of the junction interface, thereby enhancing the full well capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high ion-implant dosage is used to increase full well capacity, then the full well capacity increases, but the photodiode profile control becomes difficult
Solution Approach 1:
The patent introduces a third dimension by creating recessed portions in the photodiode structure, transforming the flat two-dimensional photodiode interface into a three-dimensional indented structure. This dimensional change increases the junction interface area without requiring higher ion-implant dosage, thus improving full well capacity while maintaining profile control precision.
Solution Approach 2:
The patent changes the geometric parameters of the photodiode structure by introducing recessed portions with specific depth and width dimensions. This parameter modification increases the effective junction area and full well capacity while keeping the ion-implant dosage within controllable ranges, resolving the contradiction between capacity and control precision.
2Quantity of substance
If ion-implant dosage is increased to improve dynamic range, then the full well capacity increases, but picture quality deteriorates due to uncontrollable photodiode profiles
Solution Approach 1:
By transitioning from a planar to a three-dimensional indented photodiode structure, the patent achieves higher full well capacity through increased junction interface area rather than increased ion-implant dosage. This maintains photodiode profile control and ensures consistent picture quality while improving dynamic range performance.
3Quantity of substance
If the photodiode structure is modified to increase junction interface area, then the full well capacity increases, but the device complexity increases
Solution Approach 1:
The patent segments the photodiode structure by introducing multiple recessed portions at different locations, which can be independently formed and controlled. This segmentation approach increases the junction interface area in a systematic way while maintaining manufacturing simplicity through standardized fabrication processes.
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 improves the full well capacity of the CMOS image sensor, leading to better dynamic range and picture quality by increasing the number of electron-hole pairs and reducing thermal budget impacts.
Implementation Method 1
the photo detecting column and the substrate are in contact with each other at a junction interface and configured as a photodiode structure to convert radiation that enters the substrate into an electrical signal
Data Source
AI summary
The present disclosure relates to a CMOS image sensor, and an associated method of formation. In some embodiments, the CMOS image sensor comprises a floating diffusion region disposed at one side of a transfer gate within a substrate and a photo detecting column disposed at the other side of the transfer gate opposing to the floating diffusion region within the substrate. The photo detecting column comprises a doped sensing layer with a doping type opposite to that of the substrate. The photo detecting column and the substrate are in contact with each other at a junction interface comprising one or more recessed portions. By forming the junction interface with recessed portions, the junction interface is enlarged compared to a previous p-n junction interface without recessed portions, and thus a full well capacity of the photodiode structure is improved.