Image Sensor Charge Transfer Gate With Adjacent P-N Regions
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Solution Overview
Problem
Image sensors suffer from white spots and dark currents due to thermally generated electron-hole pairs introduced into the photoelectric conversion region, which deteriorate their reproduction characteristics, especially after surface damage during ion implantation and etching processes.
Innovation Solution
A CMOS image sensor design featuring a charge transfer structure with a gate insulating film and a transfer gate electrode having regions doped with different conductivity types, where the potential barrier peak is closer to the photoelectric conversion region than the charge detection region, and a pinning layer to reduce thermally generated charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion implantation and etching processes are used to fabricate the image sensor, then manufacturing precision is improved, but surface damage occurs that generates thermally generated EHP's causing white spots and dark currents
Solution Approach 1:
A charge transfer structure is introduced as an intermediary component between the photoelectric conversion region and the charge detection region. This structure includes a gate insulating film and a transfer gate electrode that controls the movement of charges, preventing thermally generated EHP's from the damaged surface region from being introduced into the photoelectric conversion region while still allowing signal charges to be transferred effectively.
Solution Approach 2:
The image sensor is divided into distinct functional regions: a photoelectric conversion region, a charge transfer structure, and a charge detection region. The charge transfer structure acts as a separate stage that mediates charge movement, physically and functionally separating the photoelectric conversion region from the surface region where damage occurs, thereby preventing contamination of signal charges by thermally generated EHP's.
2Device complexity
If the surface region is damaged during fabrication, then device complexity is reduced, but thermally generated EHP's are introduced into the photoelectric conversion region causing white spots and dark currents
Solution Approach 1:
The charge transfer structure serves as a protective intermediary that prevents direct exposure of the photoelectric conversion region to thermally generated EHP's originating from the damaged surface. By controlling charge transfer through the gate electrode, it selectively allows signal charges while blocking noise charges, thereby maintaining image reproduction quality without requiring a completely undamaged surface.
3Ease of manufacture
If thermally generated EHP's are introduced into the photoelectric conversion region, then manufacturing cost is reduced, but white spots and dark currents occur that deteriorate image reproduction characteristics
Solution Approach 1:
The charge transfer structure with its gate insulating film and transfer gate electrode acts as a controlled gateway that mediates charge movement. It allows efficient transfer of signal charges from the photoelectric conversion region to the charge detection region while preventing the introduction of thermally generated EHP's from the surface, thereby maintaining high image reproduction quality without requiring prohibitively complex 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 effectively reduces the introduction of thermally generated charges into the photoelectric conversion region, thereby improving image reproduction characteristics by minimizing white spots and dark currents.
Implementation Method 1
a peak of a potential barrier that may be formed below the transfer gate electrode may be closer to the photoelectric conversion region than the charge detection region
Implementation Method 2
An image sensor is a device that may convert optical images to electrical signals
Data Source
AI summary
Example embodiments relate to an image sensor and a fabrication method thereof. An image sensor may include a semiconductor substrate. A charge transfer structure may be formed on the semiconductor substrate. The charge transfer structure may include a gate insulating film that may be formed on a channel region in the semiconductor substrate between a photoelectric conversion region and charge detection region, and a transfer gate electrode that may be formed on the gate insulating film that may have a region doped with a first conductivity type impurity-doped region and a second conductivity type impurity-doped region which may be adjacent to each other.